path: root/erts/doc/src/erlang.xml

<?xml version="1.0" encoding="utf-8" ?>
<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1996</year><year>2013</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.

    </legalnotice>

    <title>erlang</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>erlang.xml</file>
  </header>
  <module>erlang</module>
  <modulesummary>The Erlang BIFs</modulesummary>
  <description>
    <p>By convention, most built-in functions (BIFs) are seen as being
      in the module <c>erlang</c>. A number of the BIFs are viewed more
      or less as part of the Erlang programming language and are
      <em>auto-imported</em>. Thus, it is not necessary to specify
      the module name and both the calls <c>atom_to_list(Erlang)</c> and
      <c>erlang:atom_to_list(Erlang)</c> are identical.</p>
    <p>In the text, auto-imported BIFs are listed without module prefix.
      BIFs listed with module prefix are not auto-imported.</p>
    <p>BIFs may fail for a variety of reasons. All BIFs fail with
      reason <c>badarg</c> if they are called with arguments of an
      incorrect type. The other reasons that may make BIFs fail are
      described in connection with the description of each individual
      BIF.</p>
    <p>Some BIFs may be used in guard tests, these are marked with
      "Allowed in guard tests".</p>
  </description>

  <datatypes>
    <datatype>
      <name><marker id="type-ext_binary">ext_binary()</marker></name>
      <desc>
        <p>A binary data object, structured according to
           the Erlang external term format.</p>
      </desc>
    </datatype>
    <datatype>
      <name name="timestamp"></name>
      <desc><p>See <seealso marker="#timestamp/0">erlang:timestamp/0</seealso>.</p>
      </desc>
    </datatype>
    <marker id="type_time_unit"/>
    <datatype>
      <name name="time_unit"></name>
      <desc><p>Currently supported time unit representations:</p>
        <taglist>
	  <tag><c>PartsPerSecond :: integer() >= 1</c></tag>
	  <item><p>Time unit expressed in parts per second. That is,
	  the time unit equals <c>1/PartsPerSecond</c> second.</p></item>

	  <tag><c>seconds</c></tag>
	  <item><p>Symbolic representation of the time unit
	  represented by the integer <c>1</c>.</p></item>

	  <tag><c>milli_seconds</c></tag>
	  <item><p>Symbolic representation of the time unit
	  represented by the integer <c>1000</c>.</p></item>

	  <tag><c>micro_seconds</c></tag>
	  <item><p>Symbolic representation of the time unit
	  represented by the integer <c>1000000</c>.</p></item>

	  <tag><c>nano_seconds</c></tag>
	  <item><p>Symbolic representation of the time unit
	  represented by the integer <c>1000000000</c>.</p></item>

	  <tag><c>native</c></tag>
	  <item><p>Symbolic representation of the native time unit
	  used by the Erlang runtime system.</p>

	  <p>The <c>native</c> time unit is determined at
	  runtime system start, and will remain the same until
	  the runtime system terminates. If a runtime system
	  is stopped and then started again (even on the same
	  machine), the <c>native</c> time unit of the new
	  runtime system instance may differ from the
	  <c>native</c> time unit of the old runtime system
	  instance.</p>

	  <p>One can get an approximation of the <c>native</c>
	  time unit by calling <c>erlang:convert_time_unit(1,
	  seconds, native)</c>. The result equals the number
	  of whole <c>native</c> time units per second. In case
	  the number of <c>native</c> time units per second does
	  not add up to a whole number, the result will be
	  rounded downwards.</p>

	  <note>
	    <p>The value of the <c>native</c> time unit gives
	    you more or less no information at all about the
	    quality of time values. It sets a limit for
	    the
	    <seealso marker="time_correction#Time_Resolution">resolution</seealso>
	    as well as for the
	    <seealso marker="time_correction#Time_Precision">precision</seealso>
	    of time values,
	    but it gives absolutely no information at all about the
	    <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>
	    of time values. The resolution of the <c>native</c> time
	    unit and the resolution of time values may differ
	    significantly.</p>
	  </note>
	  </item>

	</taglist>

	<p>The <c>time_unit/0</c> type may be extended. Use
	<seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit/3</c></seealso>
	in order to convert time values between time units.</p>

      </desc>
    </datatype>
  </datatypes>

  <funcs>
    <func>
      <name name="abs" arity="1" clause_i="1"/>
      <name name="abs" arity="1" clause_i="2"/>
      <type variable="Float" name_i="1"/>
      <type variable="Int" name_i="2"/>
      <fsummary>Arithmetical absolute value</fsummary>
      <desc>
        <p>Returns an integer or float which is the arithmetical
          absolute value of <c><anno>Float</anno></c> or <c><anno>Int</anno></c>.</p>
        <pre>
> <input>abs(-3.33).</input>
3.33
> <input>abs(-3).</input>
3</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="adler32" arity="1"/>
      <fsummary>Compute adler32 checksum</fsummary>
      <desc>
        <p>Computes and returns the adler32 checksum for <c><anno>Data</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="adler32" arity="2"/>
      <fsummary>Compute adler32 checksum</fsummary>
      <desc>
        <p>Continue computing the adler32 checksum by combining 
	the previous checksum, <c><anno>OldAdler</anno></c>, with the checksum of
	<c><anno>Data</anno></c>.</p>
	<p>The following code:</p>
	<code>
	X = erlang:adler32(Data1),
	Y = erlang:adler32(X,Data2).
	</code>
	<p>- would assign the same value to <c>Y</c> as this would:</p>
	<code>
	Y = erlang:adler32([Data1,Data2]).
	</code>
      </desc>
    </func>
    <func>
      <name name="adler32_combine" arity="3"/>
      <fsummary>Combine two adler32 checksums</fsummary>
      <desc>
        <p>Combines two previously computed adler32 checksums. 
	This computation requires the size of the data object for 
	the second checksum to be known.</p>
	<p>The following code:</p>
	<code>
	Y = erlang:adler32(Data1),
	Z = erlang:adler32(Y,Data2).
	</code>
	<p>- would assign the same value to <c>Z</c> as this would:</p>
	<code>
	X = erlang:adler32(Data1),
	Y = erlang:adler32(Data2),
	Z = erlang:adler32_combine(X,Y,iolist_size(Data2)).
	</code>
      </desc>
    </func>
    <func>
      <name name="append_element" arity="2"/>
      <fsummary>Append an extra element to a tuple</fsummary>
      <desc>
        <p>Returns a new tuple which has one element more than
          <c><anno>Tuple1</anno></c>, and contains the elements in <c><anno>Tuple1</anno></c>
          followed by <c><anno>Term</anno></c> as the last element. Semantically
          equivalent to
          <c>list_to_tuple(tuple_to_list(<anno>Tuple1</anno>) ++ [<anno>Term</anno>])</c>, but much
          faster.</p>
        <pre>
> <input>erlang:append_element({one, two}, three).</input>
{one,two,three}</pre>
      </desc>
    </func>
    <func>
      <name name="apply" arity="2"/>
      <fsummary>Apply a function to an argument list</fsummary>
      <desc>
        <p>Call a fun, passing the elements in <c><anno>Args</anno></c> as
          arguments.</p>
        <p>Note: If the number of elements in the arguments are known at
          compile-time, the call is better written as
          <c><anno>Fun</anno>(Arg1, Arg2, ... ArgN)</c>.</p>
        <warning>
          <p>Earlier, <c><anno>Fun</anno></c> could also be given as
            <c>{Module, Function}</c>, equivalent to
            <c>apply(Module, Function, Args)</c>. This usage is
            deprecated and will stop working in a future release of
            Erlang/OTP.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="apply" arity="3"/>
      <fsummary>Apply a function to an argument list</fsummary>
      <desc>
        <p>Returns the result of applying <c>Function</c> in
          <c><anno>Module</anno></c> to <c><anno>Args</anno></c>. The applied function must
          be exported from <c>Module</c>. The arity of the function is
          the length of <c>Args</c>.</p>
        <pre>
> <input>apply(lists, reverse, [[a, b, c]]).</input>
[c,b,a]</pre>
        <p><c>apply</c> can be used to evaluate BIFs by using
          the module name <c>erlang</c>.</p>
        <pre>
> <input>apply(erlang, atom_to_list, ['Erlang']).</input>
"Erlang"</pre>
        <p>Note: If the number of arguments are known at compile-time,
          the call is better written as
          <c><anno>Module</anno>:<anno>Function</anno>(Arg1, Arg2, ..., ArgN)</c>.</p>
        <p>Failure: <c>error_handler:undefined_function/3</c> is called
          if the applied function is not exported. The error handler
          can be redefined (see
          <seealso marker="#process_flag/2">process_flag/2</seealso>).
          If the <c>error_handler</c> is undefined, or if the user has
          redefined the default <c>error_handler</c> so the replacement
          module is undefined, an error with the reason <c>undef</c>
          is generated.</p>
      </desc>
    </func>
    <func>
      <name name="atom_to_binary" arity="2"/>
      <fsummary>Return the binary representation of an atom</fsummary>
      <desc>
        <p>Returns a binary which corresponds to the text
          representation of <c><anno>Atom</anno></c>. If <c><anno>Encoding</anno></c>
	  is <c>latin1</c>, there will be one byte for each character
	  in the text representation. If <c><anno>Encoding</anno></c> is 
	  <c>utf8</c> or
	  <c>unicode</c>, the characters will be encoded using UTF-8
	  (meaning that characters from 16#80 up to 0xFF will be
	  encoded in two bytes).</p>

	<note><p>Currently, <c>atom_to_binary(<anno>Atom</anno>, latin1)</c> can
	never fail because the text representation of an atom can only contain
	characters from 0 to 16#FF. In a future release, the text representation
	of atoms might be allowed to contain any Unicode character
	and <c>atom_to_binary(<anno>Atom</anno>, latin1)</c> will fail if the
	text representation for the <c><anno>Atom</anno></c> contains a Unicode
	character greater than 16#FF.</p></note>

        <pre>
> <input>atom_to_binary('Erlang', latin1).</input>
&lt;&lt;"Erlang"&gt;&gt;</pre>
      </desc>
    </func>
    <func>
      <name name="atom_to_list" arity="1"/>
      <fsummary>Text representation of an atom</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Atom</anno></c>.</p>
        <pre>
> <input>atom_to_list('Erlang').</input>
"Erlang"</pre>
      </desc>
    </func>
    <func>
      <name name="binary_part" arity="2"/>
      <fsummary>Extracts a part of a binary</fsummary>
      <desc>
      <p>Extracts the part of the binary described by <c><anno>PosLen</anno></c>.</p>

      <p>Negative length can be used to extract bytes at the end of a binary:</p>

<code>
1> Bin = &lt;&lt;1,2,3,4,5,6,7,8,9,10&gt;&gt;.
2> binary_part(Bin,{byte_size(Bin), -5}).
&lt;&lt;6,7,8,9,10&gt;&gt;
</code>

      <p>If <c><anno>PosLen</anno></c> in any way references outside the binary, a <c>badarg</c> exception is raised.</p>

      <p><c><anno>Start</anno></c> is zero-based, i.e.:</p>
<code>
1> Bin = &lt;&lt;1,2,3&gt;&gt;
2> binary_part(Bin,{0,2}).
&lt;&lt;1,2&gt;&gt;
</code>

      <p>See the STDLIB module <c>binary</c> for details about the <c><anno>PosLen</anno></c> semantics.</p>

      <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="binary_part" arity="3"/>
      <fsummary>Extracts a part of a binary</fsummary>
      <desc>
      <p>The same as <c>binary_part(<anno>Subject</anno>, {<anno>Start</anno>, <anno>Length</anno>})</c>.</p>

      <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_atom" arity="2"/>
      <fsummary>Convert from text representation to an atom</fsummary>
      <desc>
        <p>Returns the atom whose text representation is
	<c><anno>Binary</anno></c>.  If <c><anno>Encoding</anno></c> is <c>latin1</c>, no
	translation of bytes in the binary is done. If <c><anno>Encoding</anno></c>
	is <c>utf8</c> or <c>unicode</c>, the binary must contain
	valid UTF-8 sequences; furthermore, only Unicode characters up
	to 0xFF are allowed.</p>

	<note><p><c>binary_to_atom(<anno>Binary</anno>, utf8)</c> will fail if
	the binary contains Unicode characters greater than 16#FF.
	In a future release, such Unicode characters might be allowed
	and <c>binary_to_atom(<anno>Binary</anno>, utf8)</c>
	will not fail in that case. For more information on Unicode support in atoms
	see <seealso marker="erl_ext_dist#utf8_atoms">note on UTF-8 encoded atoms</seealso>
	in the chapter about the external term format in the ERTS User's Guide.</p></note>

        <pre>
> <input>binary_to_atom(&lt;&lt;"Erlang"&gt;&gt;, latin1).</input>
'Erlang'
> <input>binary_to_atom(&lt;&lt;1024/utf8&gt;&gt;, utf8).</input>
** exception error: bad argument
     in function  binary_to_atom/2
        called as binary_to_atom(&lt;&lt;208,128&gt;&gt;,utf8)</pre>
      </desc>
    </func>
    <func>
      <name name="binary_to_existing_atom" arity="2"/>
      <fsummary>Convert from text representation to an atom</fsummary>
      <desc>
        <p>Works like <seealso marker="#binary_to_atom/2">binary_to_atom/2</seealso>,
          but the atom must already exist.</p>
        <p>Failure: <c>badarg</c> if the atom does not already exist.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_float" arity="1"/>
      <fsummary>Convert from text representation to a float</fsummary>
      <desc>
        <p>Returns the float whose text representation is <c><anno>Binary</anno></c>.</p>
        <pre>
> <input>binary_to_float(&lt;&lt;"2.2017764e+0">>).</input>
2.2017764</pre>
        <p>Failure: <c>badarg</c> if <c><anno>Binary</anno></c> contains a bad
          representation of a float.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_integer" arity="1"/>
      <fsummary>Convert from text representation to an integer</fsummary>
      <desc>
        <p>Returns an integer whose text representation is
          <c><anno>Binary</anno></c>.</p>
        <pre>
> <input>binary_to_integer(&lt;&lt;"123"&gt;&gt;).</input>
123</pre>
        <p>Failure: <c>badarg</c> if <c><anno>Binary</anno></c> contains a bad
          representation of an integer.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_integer" arity="2"/>
      <fsummary>Convert from text representation to an integer</fsummary>
      <desc>
        <p>Returns an integer whose text representation in base
          <c><anno>Base</anno></c> is <c><anno>Binary</anno></c>.</p>
        <pre>
> <input>binary_to_integer(&lt;&lt;"3FF"&gt;&gt;, 16).</input>
1023</pre>
        <p>Failure: <c>badarg</c> if <c><anno>Binary</anno></c> contains a bad
          representation of an integer.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_list" arity="1"/>
      <fsummary>Convert a binary to a list</fsummary>
      <desc>
        <p>Returns a list of integers which correspond to the bytes of
          <c><anno>Binary</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_list" arity="3"/>
      <fsummary>Convert part of a binary to a list</fsummary>
      <type_desc variable="Start">1..byte_size(<anno>Binary</anno>)</type_desc>
      <desc>
        <p>As <c>binary_to_list/1</c>, but returns a list of integers
          corresponding to the bytes from position <c><anno>Start</anno></c> to
          position <c><anno>Stop</anno></c> in <c><anno>Binary</anno></c>. Positions in the
          binary are numbered starting from 1.</p>

	  <note><p>This function's indexing style of using one-based indices for
	  binaries is deprecated. New code should use the functions in
	  the STDLIB module <c>binary</c> instead. They consequently
	  use the same (zero-based) style of indexing.</p></note>
      </desc>
    </func>
    <func>
      <name name="bitstring_to_list" arity="1"/>
      <fsummary>Convert a bitstring to a list</fsummary>
      <desc>
        <p>Returns a list of integers which correspond to the bytes of
          <c><anno>Bitstring</anno></c>. If the number of bits in the binary is not
	  divisible by 8, the last element of the list will be a bitstring
	  containing the remaining bits (1 up to 7 bits).</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_term" arity="1"/>
      <fsummary>Decode an Erlang external term format binary</fsummary>
      <desc>
        <p>Returns an Erlang term which is the result of decoding
          the binary object <c><anno>Binary</anno></c>, which must be encoded
          according to the Erlang external term format.</p>
        <warning>
	  <p>When decoding binaries from untrusted sources, consider using
	     <c>binary_to_term/2</c> to prevent denial of service attacks.</p>
        </warning>
	<p>See also
	   <seealso marker="#term_to_binary/1">term_to_binary/1</seealso>
           and
	   <seealso marker="#binary_to_term/2">binary_to_term/2</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="binary_to_term" arity="2"/>
      <fsummary>Decode an Erlang external term format binary</fsummary>
      <desc>
        <p>As <c>binary_to_term/1</c>, but takes options that affect decoding
           of the binary.</p>
        <taglist>
          <tag><c>safe</c></tag>
          <item>
	    <p>Use this option when receiving binaries from an untrusted
               source.</p>
	    <p>When enabled, it prevents decoding data that may be used to
	       attack the Erlang system.  In the event of receiving unsafe
               data, decoding fails with a badarg error.</p>
	    <p>Currently, this prevents creation of new atoms directly,
	       creation of new atoms indirectly (as they are embedded in
	       certain structures like pids, refs, funs, etc.), and creation of
	       new external function references.  None of those resources are
	       currently garbage collected, so unchecked creation of them can
               exhaust available memory.</p>
          </item>
        </taglist>
	<p>Failure: <c>badarg</c> if <c>safe</c> is specified and unsafe data
           is decoded.</p>
        <p>See also
           <seealso marker="#term_to_binary/1">term_to_binary/1</seealso>,
           <seealso marker="#binary_to_term/1">binary_to_term/1</seealso>,
           and <seealso marker="#list_to_existing_atom/1">
             list_to_existing_atom/1</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="bit_size" arity="1"/>
      <fsummary>Return the size of a bitstring</fsummary>
      <desc>
        <p>Returns an integer which is the size in bits of <c><anno>Bitstring</anno></c>.</p>
        <pre>
> <input>bit_size(&lt;&lt;433:16,3:3&gt;&gt;).</input>
19
> <input>bit_size(&lt;&lt;1,2,3&gt;&gt;).</input>
24</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="bump_reductions" arity="1"/>
      <fsummary>Increment the reduction counter</fsummary>
      <desc>
        <p>This implementation-dependent function increments
          the reduction counter for the calling process. In the Beam
          emulator, the reduction counter is normally incremented by
          one for each function and BIF call, and a context switch is
          forced when the counter reaches the maximum number of reductions
	  for a process (2000 reductions in R12B).</p>
        <warning>
          <p>This BIF might be removed in a future version of the Beam
            machine without prior warning. It is unlikely to be
            implemented in other Erlang implementations.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="byte_size" arity="1"/>
      <fsummary>Return the size of a bitstring (or binary)</fsummary>
      <desc>
        <p>Returns an integer which is the number of bytes needed to contain
	<c><anno>Bitstring</anno></c>. (That is, if the number of bits in <c><anno>Bitstring</anno></c> is not
	divisible by 8, the resulting number of bytes will be rounded <em>up</em>.)</p>
        <pre>
> <input>byte_size(&lt;&lt;433:16,3:3&gt;&gt;).</input>
3
> <input>byte_size(&lt;&lt;1,2,3&gt;&gt;).</input>
3</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="cancel_timer" arity="2"/>
      <fsummary>Cancel a timer</fsummary>
      <desc>
        <p>
	  Cancels a timer that has been created by either
	  <seealso marker="#start_timer/4"><c>erlang:start_timer()</c></seealso>,
	  or <seealso marker="#send_after/4"><c>erlang:send_after()</c></seealso>.
	  <c><anno>TimerRef</anno></c> identifies the timer, and
	  was returned by the BIF that created the timer.
	</p>
	<p>Currently available <c><anno>Option</anno></c>s:</p>
        <taglist>
          <tag><c>{async, Async}</c></tag>
          <item>
	    <p>
	      Asynchronous request for cancellation. <c>Async</c>
	      defaults to <c>false</c> which will cause the
	      cancellation to be performed synchronously. When
	      <c>Async</c> is set to <c>true</c>, the cancel
	      operation will be performed asynchronously. That is,
	      <c>erlang:cancel_timer()</c> will send an asynchronous
	      request for cancellation to the timer service that
	      manages the timer, and then return <c>ok</c>.
	  </p>
	  </item>
          <tag><c>{info, Info}</c></tag>
          <item>
	    <p>
	      Request information about the <c><anno>Result</anno></c>
	      of the cancellation. <c>Info</c> defaults to <c>true</c>
	      which means that the <c><anno>Result</anno></c> will
	      be given. When <c>Info</c> is set to <c>false</c>, no
	      information about the result of the cancellation
	      will be given. When the operation is performed</p>
              <taglist>
		<tag>synchronously</tag>
		<item>
		  <p>
		    If <c>Info</c> is <c>true</c>, the <c>Result</c> will
		    returned by <c>erlang:cancel_timer()</c>; otherwise,
		    <c>ok</c> will be returned.
		  </p>
		</item>
		<tag>asynchronously</tag>
		<item>
		  <p>
		    If <c>Info</c> is <c>true</c>, a message on the form
		    <c>{cancel_timer, <anno>TimerRef</anno>,
		    <anno>Result</anno>}</c> will be sent to the
		    caller of <c>erlang:cancel_timer()</c> when the
		    cancellation operation has been performed; otherwise,
		    no message will be sent.
		  </p>
		</item>
            </taglist>
	  </item>
        </taglist>
	<p>
	  More <c><anno>Option</anno></c>s may be added in the future.
	</p>
	<p>
	  When the <c><anno>Result</anno></c> equals <c>false</c>, a
	  timer corresponding to <c><anno>TimerRef</anno></c> could not
	  be found. This can be either because the timer had expired,
	  already had been canceled, or because <c><anno>TimerRef</anno></c>
	  never has corresponded to a timer. If the timer has expired,
	  the timeout message has been sent, but it does not tell you
	  whether or not it has arrived at its destination yet. When the
	  <c><anno>Result</anno></c> is an integer, it represents the
	  time in milli-seconds left until the timer will expire.
	</p>
	<note>
	  <p>
	    The timer service that manages the timer may be co-located
	    with another scheduler than the scheduler that the calling
	    process is executing on. If this is the case, communication
	    with the timer service will take much longer time than if it
	    is located locally. If the calling process is in critical
	    path, and can do other things while waiting for the result
	    of this operation, or is not interested in the result of
	    the operation, you want to use the <c>{async, true}</c>
	    option. If using the <c>{async, false}</c> option, the calling
	    process will be blocked until the operation has been
	    performed.
	  </p>
	</note>
        <p>See also 
          <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>,
          <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>,
          and
          <seealso marker="#read_timer/2"><c>erlang:read_timer/2</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="cancel_timer" arity="1"/>
      <fsummary>Cancel a timer</fsummary>
      <desc>
        <p>Cancels a timer. The same as calling
	<seealso marker="#cancel_timer/2"><c>erlang:cancel_timer(TimerRef,
	[])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="check_old_code" arity="1"/>
      <fsummary>Check if a module has old code</fsummary>
      <desc>
        <p>Returns <c>true</c> if the <c><anno>Module</anno></c> has old code,
	and <c>false</c> otherwise.</p>
        <p>See also <seealso marker="kernel:code">code(3)</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="check_process_code" arity="2"/>
      <fsummary>Check if a process is executing old code for a module</fsummary>
      <desc>
        <p>The same as
	<seealso marker="#check_process_code/3"><c>erlang:check_process_code(<anno>Pid</anno>,
	<anno>Module</anno>, [])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="check_process_code" arity="3"/>
      <fsummary>Check if a process is executing old code for a module</fsummary>
      <desc>
	<p>Check if the node local process identified by <c><anno>Pid</anno></c>
	is executing old code for <c><anno>Module</anno></c>.</p>
	<p>Currently available <c><anno>Option</anno>s</c>:</p>
        <taglist>
          <tag><c>{allow_gc, boolean()}</c></tag>
          <item>
	    Determines if garbage collection is allowed when performing
	    the operation. If <c>{allow_gc, false}</c> is passed, and
	    a garbage collection is needed in order to determine the
	    result of the operation, the operation will be aborted
	    (see information on <c><anno>CheckResult</anno></c> below).
	    The default is to allow garbage collection, i.e.,
	    <c>{allow_gc, true}</c>.
	  </item>
          <tag><c>{async, RequestId}</c></tag>
          <item>
	    The <c>check_process_code/3</c> function will return
	    the value <c>async</c> immediately after the request
	    has been sent. When the request has been processed, the
	    process that called this function will be passed a
	    message on the form:<br/>
	    <c>{check_process_code, <anno>RequestId</anno>, <anno>CheckResult</anno>}</c>.
	  </item>
        </taglist>
	<p>If <c><anno>Pid</anno></c> equals <c>self()</c>, and
	no <c>async</c> option has been passed, the operation will
	be performed at once. In all other cases a request for
	the operation will be sent to the process identified by
	<c><anno>Pid</anno></c>, and will be handled when
	appropriate. If no <c>async</c> option has been passed,
	the caller will block until <c><anno>CheckResult</anno></c>
	is available and can be returned.</p>
	<p><c><anno>CheckResult</anno></c> informs about the result of
	the request:</p>
        <taglist>
          <tag><c>true</c></tag>
          <item>
	    The process identified by <c><anno>Pid</anno></c> is
	    executing old code for <c><anno>Module</anno></c>.
	    That is, the current call of the process executes old
	    code for this module, or the process has references
	    to old code for this module, or the process contains
	    funs that references old code for this module.
	  </item>
          <tag><c>false</c></tag>
          <item>
	    The process identified by <c><anno>Pid</anno></c> is
	    not executing old code for <c><anno>Module</anno></c>.
	  </item>
          <tag><c>aborted</c></tag>
          <item>
	    The operation was aborted since the process needed to
	    be garbage collected in order to determine the result
	    of the operation, and the operation was requested
	    by passing the <c>{allow_gc, false}</c> option.</item>
        </taglist>
        <p>See also <seealso marker="kernel:code">code(3)</seealso>.</p>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>Pid</anno></c> is not a node local process identifier.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>Module</anno></c> is not an atom.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>OptionList</anno></c> is not a valid list of options.
	  </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="convert_time_unit" arity="3"/>
      <fsummary>Convert time unit of a time value</fsummary>
      <desc>
	<p>Converts the <c><anno>Time</anno></c> value of time unit
	<c><anno>FromUnit</anno></c> to the corresponding
	<c><anno>ConvertedTime</anno></c> value of time unit
	<c><anno>ToUnit</anno></c>. The result is rounded
	using the floor function.</p>

	<warning><p>You may lose accuracy and precision when converting
	between	time units. In order to minimize such loss, collect all
	data at <c>native</c> time unit and do the conversion on the end
	result.</p></warning>
      </desc>
    </func>
    <func>
      <name name="crc32" arity="1"/>
      <fsummary>Compute crc32 (IEEE 802.3) checksum</fsummary>
      <desc>
        <p>Computes and returns the crc32 (IEEE 802.3 style) checksum for <c><anno>Data</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="crc32" arity="2"/>
      <fsummary>Compute crc32 (IEEE 802.3) checksum</fsummary>
      <desc>
        <p>Continue computing the crc32 checksum by combining 
	the previous checksum, <c><anno>OldCrc</anno></c>, with the checksum of
	<c><anno>Data</anno></c>.</p>
	<p>The following code:</p>
	<code>
	X = erlang:crc32(Data1),
	Y = erlang:crc32(X,Data2).
	</code>
	<p>- would assign the same value to <c>Y</c> as this would:</p>
	<code>
	Y = erlang:crc32([Data1,Data2]).
	</code>
      </desc>
    </func>
    <func>
      <name name="crc32_combine" arity="3"/>
      <fsummary>Combine two crc32 (IEEE 802.3) checksums</fsummary>
      <desc>
        <p>Combines two previously computed crc32 checksums. 
	This computation requires the size of the data object for 
	the second checksum to be known.</p>
	<p>The following code:</p>
	<code>
	Y = erlang:crc32(Data1),
	Z = erlang:crc32(Y,Data2).
	</code>
	<p>- would assign the same value to <c>Z</c> as this would:</p>
	<code>
	X = erlang:crc32(Data1),
	Y = erlang:crc32(Data2),
	Z = erlang:crc32_combine(X,Y,iolist_size(Data2)).
	</code>
      </desc>
    </func>
    <func>
      <name name="date" arity="0"/>
      <fsummary>Current date</fsummary>
      <desc>
        <p>Returns the current date as <c>{Year, Month, Day}</c>.</p>
        <p>The time zone and daylight saving time correction depend on
          the underlying OS.</p>
        <pre>
> <input>date().</input>
{1995,2,19}</pre>
      </desc>
    </func>
    <func>
      <name name="decode_packet" arity="3"/>
      <fsummary>Extracts a protocol packet from a binary</fsummary>
      <desc>

        <p>Decodes the binary <c><anno>Bin</anno></c> according to the packet
        protocol specified by <c><anno>Type</anno></c>. Very similar to the packet
        handling done by sockets with the option {packet,<anno>Type</anno>}.</p>
        <p>If an entire packet is contained in <c><anno>Bin</anno></c> it is
        returned together with the remainder of the binary as
        <c>{ok,<anno>Packet</anno>,<anno>Rest</anno>}</c>.</p>
        <p>If <c><anno>Bin</anno></c> does not contain the entire packet,
        <c>{more,<anno>Length</anno>}</c> is returned. <c><anno>Length</anno></c> is either the
        expected <em>total size</em> of the packet or <c>undefined</c>
        if the expected packet size is not known. <c>decode_packet</c>
        can then be called again with more data added.</p>
        <p>If the packet does not conform to the protocol format
        <c>{error,<anno>Reason</anno>}</c> is returned.</p>
        <p>The following values of <c><anno>Type</anno></c> are valid:</p>
        <taglist>
          <tag><c>raw | 0</c></tag>
          <item>
            <p>No packet handling is done. Entire binary is
            returned unless it is empty.</p>
          </item>
          <tag><c>1 | 2 | 4</c></tag>
          <item>
            <p>Packets consist of a header specifying the number of
              bytes in the packet, followed by that number of bytes.
              The length of header can be one, two, or four bytes;
              the order of the bytes is big-endian. The header
              will be stripped off when the packet is returned.</p>
          </item>
          <tag><c>line</c></tag>
          <item>
            <p>A packet is a line terminated with newline. The
              newline character is included in the returned packet
              unless the line was truncated according to the option
              <c>line_length</c>.</p> 
          </item>
          <tag><c>asn1 | cdr | sunrm | fcgi | tpkt</c></tag>
          <item>
            <p>The header is <em>not</em> stripped off.</p>
            <p>The meanings of the packet types are as follows:</p>
            <taglist>     
              <tag><c>asn1</c> - ASN.1 BER</tag><item></item>
              <tag><c>sunrm</c> - Sun's RPC encoding</tag><item></item>
              <tag><c>cdr</c> - CORBA (GIOP 1.1)</tag><item></item>
              <tag><c>fcgi</c> - Fast CGI</tag><item></item>
              <tag><c>tpkt</c> - TPKT format [RFC1006]</tag><item></item>
            </taglist>
          </item>
          <tag><c>http | httph | http_bin | httph_bin</c></tag>
          <item>
            <p>The Hypertext Transfer Protocol. The packets
               are returned with the format according to
               <c><anno>HttpPacket</anno></c> described above. A packet is either a
               request, a response, a header or an end of header
               mark. Invalid lines are returned as <c><anno>HttpError</anno></c>.</p>
            <p>Recognized request methods and header fields are returned as atoms.
               Others are returned as strings. Strings of unrecognized header fields
	       are formatted with only capital letters first and after hyphen characters
	       (like <c>"Sec-Websocket-Key"</c>).</p>
            <p>The protocol type <c>http</c> should only be used for
               the first line when a <c><anno>HttpRequest</anno></c> or a
               <c><anno>HttpResponse</anno></c> is expected. The following calls
               should use <c>httph</c> to get <c><anno>HttpHeader</anno></c>'s until
               <c>http_eoh</c> is returned that marks the end of the
               headers and the beginning of any following message body.</p> 
            <p>The variants <c>http_bin</c> and <c>httph_bin</c> will return
               strings (<c>HttpString</c>) as binaries instead of lists.</p>
          </item>
        </taglist>
        <p>The following options are available:</p>
            <taglist>
              <tag><c>{packet_size, integer() >= 0}</c></tag>
              <item><p>Sets the max allowed size of the packet body. If
                the packet header indicates that the length of the
                packet is longer than the max allowed length, the packet
                is considered invalid. Default is 0 which means no
                size limit.</p>
              </item>
              <tag><c>{line_length, integer() >= 0}</c></tag>
              <item><p>For packet type <c>line</c>, truncate lines longer
	      than the indicated length.</p>
	      <p>Option <c>line_length</c> also applies to <c>http*</c> 
	      packet types as an alias for option <c>packet_size</c> in the
	      case when <c>packet_size</c> itself is not set. This usage is
	      only intended for backward compatibility.</p>
              </item>
            </taglist>
        <pre>
> <input>erlang:decode_packet(1,&lt;&lt;3,"abcd"&gt;&gt;,[]).</input>
{ok,&lt;&lt;"abc"&gt;&gt;,&lt;&lt;"d"&gt;&gt;}
> <input>erlang:decode_packet(1,&lt;&lt;5,"abcd"&gt;&gt;,[]).</input>
{more,6}</pre>
      </desc>
    </func>

    <func>
      <name name="delete_element" arity="2"/>
      <fsummary>Delete element at index in a tuple</fsummary>
      <type_desc variable="Index">1..tuple_size(<anno>Tuple1</anno>)</type_desc>
      <desc>
		  <p>
			  Returns a new tuple with element at <c><anno>Index</anno></c> removed from
			  tuple <c><anno>Tuple1</anno></c>.
		  </p>
        <pre>
> <input>erlang:delete_element(2, {one, two, three}).</input>
{one,three}</pre>
      </desc>
    </func>

    <func>
      <name name="delete_module" arity="1"/>
      <fsummary>Make the current code for a module old</fsummary>
      <desc>
        <p>Makes the current code for <c><anno>Module</anno></c> become old code, and
          deletes all references for this module from the export table.
          Returns <c>undefined</c> if the module does not exist,
          otherwise <c>true</c>.</p>
        <warning>
          <p>This BIF is intended for the code server (see
            <seealso marker="kernel:code">code(3)</seealso>) and should not be
            used elsewhere.</p>
        </warning>
        <p>Failure: <c>badarg</c> if there is already an old version of
          <c>Module</c>.</p>
      </desc>
    </func>
    <func>
      <name name="demonitor" arity="1"/>
      <fsummary>Stop monitoring</fsummary>
      <desc>
        <p>If <c><anno>MonitorRef</anno></c> is a reference which the calling process
          obtained by calling
          <seealso marker="#monitor/2">monitor/2</seealso>,
          this monitoring is turned off. If the monitoring is already
          turned off, nothing happens.</p>
        <p>Once <c>demonitor(<anno>MonitorRef</anno>)</c> has returned it is
          guaranteed that no <c>{'DOWN', <anno>MonitorRef</anno>, _, _, _}</c> message
          due to the monitor will be placed in the caller's message queue
          in the future. A <c>{'DOWN', <anno>MonitorRef</anno>, _, _, _}</c> message
          might have been placed in the caller's message queue prior to
          the call, though. Therefore, in most cases, it is advisable
          to remove such a <c>'DOWN'</c> message from the message queue
          after monitoring has been stopped. 
          <seealso marker="#demonitor/2">demonitor(<anno>MonitorRef</anno>, [flush])</seealso> can be used instead of
          <c>demonitor(<anno>MonitorRef</anno>)</c> if this cleanup is wanted.</p>
        <note>
          <p>Prior to OTP release R11B (erts version 5.5) <c>demonitor/1</c>
            behaved completely asynchronous, i.e., the monitor was active
            until the "demonitor signal" reached the monitored entity. This
            had one undesirable effect, though. You could never know when
            you were guaranteed <em>not</em> to receive a <c>DOWN</c> message
            due to the monitor.</p>
          <p>Current behavior can be viewed as two combined operations:
            asynchronously send a "demonitor signal" to the monitored entity
            and ignore any future results of the monitor. </p>
        </note>
        <p>Failure: It is an error if <c><anno>MonitorRef</anno></c> refers to a
          monitoring started by another process. Not all such cases are
          cheap to check; if checking is cheap, the call fails with
          <c>badarg</c> (for example if <c><anno>MonitorRef</anno></c> is a remote
          reference).</p>
      </desc>
    </func>
    <func>
      <name name="demonitor" arity="2"/>
      <fsummary>Stop monitoring</fsummary>
      <desc>
        <p>The returned value is <c>true</c> unless <c>info</c> is part
	   of <c><anno>OptionList</anno></c>.
	</p>
        <p><c>demonitor(<anno>MonitorRef</anno>, [])</c> is equivalent to
          <seealso marker="#demonitor/1">demonitor(<anno>MonitorRef</anno>)</seealso>.</p>
        <p>Currently the following <c><anno>Option</anno></c>s are valid:</p>
        <taglist>
          <tag><c>flush</c></tag>
          <item>
            <p>Remove (one) <c>{_, <anno>MonitorRef</anno>, _, _, _}</c> message,
              if there is one, from the caller's message queue after
              monitoring has been stopped.</p>
            <p>Calling <c>demonitor(<anno>MonitorRef</anno>, [flush])</c>
              is equivalent to the following, but more efficient:</p>
            <code type="none">

    demonitor(MonitorRef),
    receive
        {_, MonitorRef, _, _, _} ->
            true
    after 0 ->
            true
    end</code>
          </item>
          <tag><c>info</c></tag>
          <item>
	    <p>The returned value is one of the following:</p>
	    <taglist>
	      <tag><c>true</c></tag>
	      <item><p>The monitor was found and removed. In this case
		       no <c>'DOWN'</c> message due to this monitor have
		       been nor will be placed in the message queue
		       of the caller.
		    </p>
	      </item>
	      <tag><c>false</c></tag>
	      <item><p>The monitor was not found and could not be removed.
	      	       This probably because someone already has placed a
		       <c>'DOWN'</c> message corresponding to this monitor
		       in the caller's message queue.
		    </p>
	      </item>
	    </taglist>
	    <p>If the <c>info</c> option is combined with the <c>flush</c>
	       option, <c>false</c> will be returned if a flush was needed;
	       otherwise, <c>true</c>.
	    </p>
          </item>
        </taglist>
        <note>
          <p>More options may be added in the future.</p>
        </note>
        <p>Failure: <c>badarg</c> if <c><anno>OptionList</anno></c> is not a list, or
          if <c><anno>Option</anno></c> is not a valid option, or the same failure as for
          <seealso marker="#demonitor/1">demonitor/1</seealso></p>
      </desc>
    </func>
    <func>
      <name name="disconnect_node" arity="1"/>
      <fsummary>Force the disconnection of a node</fsummary>
      <desc>
        <p>Forces the disconnection of a node. This will appear to
          the node <c><anno>Node</anno></c> as if the local node has crashed. This
          BIF is mainly used in the Erlang network authentication
          protocols. Returns <c>true</c> if disconnection succeeds,
          otherwise <c>false</c>. If the local node is not alive,
          the function returns <c>ignored</c>.</p>
      </desc>
    </func>
    <func>
      <name name="display" arity="1"/>
      <fsummary>Print a term on standard output</fsummary>
      <desc>
        <p>Prints a text representation of <c><anno>Term</anno></c> on the standard
          output. On OSE the term is printed to the ramlog.</p>
        <warning>
          <p>This BIF is intended for debugging only.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="element" arity="2"/>
      <type_desc variable="N">1..tuple_size(<anno>Tuple</anno>)</type_desc>
      <fsummary>Get Nth element of a tuple</fsummary>
      <desc>
        <p>Returns the <c><anno>N</anno></c>th element (numbering from 1) of
          <c><anno>Tuple</anno></c>.</p>
        <pre>
> <input>element(2, {a, b, c}).</input>
b</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="erase" arity="0"/>
      <fsummary>Return and delete the process dictionary</fsummary>
      <desc>
        <p>Returns the process dictionary and deletes it.</p>
        <pre>
> <input>put(key1, {1, 2, 3}),</input>
<input>put(key2, [a, b, c]),</input>
<input>erase().</input>
[{key1,{1,2,3}},{key2,[a,b,c]}]</pre>
      </desc>
    </func>
    <func>
      <name name="erase" arity="1"/>
      <fsummary>Return and delete a value from the process dictionary</fsummary>
      <desc>
        <p>Returns the value <c><anno>Val</anno></c> associated with <c><anno>Key</anno></c> and
          deletes it from the process dictionary. Returns
          <c>undefined</c> if no value is associated with <c><anno>Key</anno></c>.</p>
        <pre>
> <input>put(key1, {merry, lambs, are, playing}),</input>
<input>X = erase(key1),</input>
<input>{X, erase(key1)}.</input>
{{merry,lambs,are,playing},undefined}</pre>
      </desc>
    </func>
    <func>
      <name name="error" arity="1"/>
      <fsummary>Stop execution with a given reason</fsummary>
      <desc>
        <p>Stops the execution of the calling process with the reason
          <c><anno>Reason</anno></c>, where <c><anno>Reason</anno></c> is any term. The actual
          exit reason will be <c>{<anno>Reason</anno>, Where}</c>, where <c>Where</c>
          is a list of the functions most recently called (the current
          function first). Since evaluating this function causes
          the process to terminate, it has no return value.</p>
        <pre>
> <input>catch error(foobar).</input>
{'EXIT',{foobar,[{erl_eval,do_apply,5},
                 {erl_eval,expr,5},
                 {shell,exprs,6},
                 {shell,eval_exprs,6},
                 {shell,eval_loop,3}]}}</pre>
      </desc>
    </func>
    <func>
      <name name="error" arity="2"/>
      <fsummary>Stop execution with a given reason</fsummary>
      <desc>
        <p>Stops the execution of the calling process with the reason
          <c><anno>Reason</anno></c>, where <c><anno>Reason</anno></c> is any term. The actual
          exit reason will be <c>{<anno>Reason</anno>, Where}</c>, where <c>Where</c>
          is a list of the functions most recently called (the current
          function first). <c><anno>Args</anno></c> is expected to be the list of
          arguments for the current function; in Beam it will be used
          to provide the actual arguments for the current function in
          the <c>Where</c> term. Since evaluating this function causes
          the process to terminate, it has no return value.</p>
      </desc>
    </func>
    <func>
      <name name="exit" arity="1"/>
      <fsummary>Stop execution with a given reason</fsummary>
      <desc>
        <p>Stops the execution of the calling process with the exit
          reason <c><anno>Reason</anno></c>, where <c><anno>Reason</anno></c> is any term. Since
          evaluating this function causes the process to terminate, it
          has no return value.</p>
        <pre>
> <input>exit(foobar).</input>
** exception exit: foobar
> <input>catch exit(foobar).</input>
{'EXIT',foobar}</pre>
      </desc>
    </func>
    <func>
      <name name="exit" arity="2"/>
      <fsummary>Send an exit signal to a process or a port</fsummary>
      <desc>
        <p>Sends an exit signal with exit reason <c><anno>Reason</anno></c> to
          the process or port identified by <c><anno>Pid</anno></c>.</p>
        <p>The following behavior apply if <c><anno>Reason</anno></c> is any term
          except <c>normal</c> or <c>kill</c>:</p>
        <p>If <c><anno>Pid</anno></c> is not trapping exits, <c><anno>Pid</anno></c> itself will
          exit with exit reason <c><anno>Reason</anno></c>. If <c><anno>Pid</anno></c> is trapping
          exits, the exit signal is transformed into a message
          <c>{'EXIT', From, <anno>Reason</anno>}</c> and delivered to the message
          queue of <c><anno>Pid</anno></c>. <c>From</c> is the pid of the process
          which sent the exit signal. See also
          <seealso marker="#process_flag/2">process_flag/2</seealso>.</p>
        <p>If <c><anno>Reason</anno></c> is the atom <c>normal</c>, <c><anno>Pid</anno></c> will
          not exit. If it is trapping exits, the exit signal is
          transformed into a message <c>{'EXIT', From, normal}</c>
          and delivered to its message queue.</p>
        <p>If <c><anno>Reason</anno></c> is the atom <c>kill</c>, that is if
          <c>exit(<anno>Pid</anno>, kill)</c> is called, an untrappable exit signal
          is sent to <c><anno>Pid</anno></c> which will unconditionally exit with
          exit reason <c>killed</c>.</p>
      </desc>
    </func>
    <func>
      <name name="external_size" arity="1"/>
      <fsummary>Calculate the maximum size for a term encoded in the Erlang
        external term format</fsummary>
      <desc>
        <p>Calculates, without doing the encoding, the maximum byte size for
          a term encoded in the Erlang external term format. The following
          condition applies always:</p>
        <p>
          <pre>
> <input>Size1 = byte_size(term_to_binary(<anno>Term</anno>)),</input>
> <input>Size2 = erlang:external_size(<anno>Term</anno>),</input>
> <input>true = Size1 =&lt; Size2.</input>
true
          </pre>
        </p>
        <p>This is equivalent to a call to: <code>erlang:external_size(<anno>Term</anno>, [])
          </code></p>
      </desc>
    </func>
    <func>
      <name name="external_size" arity="2"/>
      <fsummary>Calculate the maximum size for a term encoded in the Erlang
        external term format</fsummary>
      <desc>
        <p>Calculates, without doing the encoding, the maximum byte size for
          a term encoded in the Erlang external term format. The following
          condition applies always:</p>
        <p>
          <pre>
> <input>Size1 = byte_size(term_to_binary(<anno>Term</anno>, <anno>Options</anno>)),</input>
> <input>Size2 = erlang:external_size(<anno>Term</anno>, <anno>Options</anno>),</input>
> <input>true = Size1 =&lt; Size2.</input>
true
          </pre>
        </p>
        <p>The option <c>{minor_version, <anno>Version</anno>}</c> specifies how floats
          are encoded. See
          <seealso marker="#term_to_binary/2">term_to_binary/2</seealso> for
          a more detailed description.
        </p>
      </desc>
    </func>
    <func>
      <name name="float" arity="1"/>
      <fsummary>Convert a number to a float</fsummary>
      <desc>
        <p>Returns a float by converting <c><anno>Number</anno></c> to a float.</p>
        <pre>
> <input>float(55).</input>
55.0</pre>
        <p>Allowed in guard tests.</p>
        <note>
          <p>Note that if used on the top-level in a guard, it will
            test whether the argument is a floating point number; for
            clarity, use
            <seealso marker="#is_float/1">is_float/1</seealso> instead.</p>
          <p>When <c>float/1</c> is used in an expression in a guard,
            such as '<c>float(A) == 4.0</c>', it converts a number as
            described above.</p>
        </note>
      </desc>
    </func>
    <func>
      <name name="float_to_binary" arity="1"/>
      <fsummary>Text representation of a float</fsummary>
      <desc>
        <p>The same as <c>float_to_binary(<anno>Float</anno>,[{scientific,20}])</c>.</p>
      </desc>
    </func>
    <func>
      <name name="float_to_binary" arity="2"/>
      <fsummary>Text representation of a float formatted using given options</fsummary>
      <desc>
        <p>Returns a binary which corresponds to the text
          representation of <c><anno>Float</anno></c> using fixed decimal 
	  point formatting. The <c><anno>Options</anno></c> behave in the same
	  way as <seealso marker="#float_to_list/2">float_to_list/2</seealso>.
	</p>
        <pre>
> <input>float_to_binary(7.12, [{decimals, 4}]).</input>
&lt;&lt;"7.1200">>
> <input>float_to_binary(7.12, [{decimals, 4}, compact]).</input>
&lt;&lt;"7.12">></pre>
      </desc>
    </func>
    <func>
      <name name="float_to_list" arity="1"/>
      <fsummary>Text representation of a float</fsummary>
      <desc>
	<p>The same as <c>float_to_list(<anno>Float</anno>,[{scientific,20}])</c>.</p>
      </desc>
    </func>
    <func>
      <name name="float_to_list" arity="2"/>
      <fsummary>Text representation of a float formatted using given options</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c>Float</c> using fixed decimal point formatting.
          When <c>decimals</c> option is specified
          the returned value will contain at most <c>Decimals</c> number of
          digits past the decimal point.  If the number doesn't fit in the
          internal static buffer of 256 bytes, the function throws <c>badarg</c>.
          When <c>compact</c> option is provided
          the trailing zeros at the end of the list are truncated (this option is
          only meaningful together with the <c>decimals</c> option). When
          <c>scientific</c> option is provided, the float will be formatted using
          scientific notation with <c>Decimals</c> digits of precision. If
          <c>Options</c> is <c>[]</c> the function behaves like 
	  <c><seealso marker="#float_to_list/1">float_to_list/1</seealso></c>.
          </p>
        <pre>
> <input>float_to_list(7.12, [{decimals, 4}]).</input>
"7.1200"
> <input>float_to_list(7.12, [{decimals, 4}, compact]).</input>
"7.12"</pre>
      </desc>
    </func>
    <func>
      <name name="fun_info" arity="1"/>
      <fsummary>Information about a fun</fsummary>
      <desc>
        <p>Returns a list containing information about the fun
          <c><anno>Fun</anno></c>. Each element of the list is a tuple. The order of
          the tuples is not defined, and more tuples may be added in a
          future release.</p>
        <warning>
          <p>This BIF is mainly intended for debugging, but it can
            occasionally be useful in library functions that might need
            to verify, for instance, the arity of a fun.</p>
        </warning>
        <p>There are two types of funs with slightly different
          semantics:</p>
        <p>A fun created by <c>fun M:F/A</c> is called an
          <em>external</em> fun. Calling it will always call the
          function <c>F</c> with arity <c>A</c> in the latest code for
          module <c>M</c>. Note that module <c>M</c> does not even need
          to be loaded when the fun <c>fun M:F/A</c> is created.</p>
        <p>All other funs are called <em>local</em>. When a local fun
          is called, the same version of the code that created the fun
          will be called (even if newer version of the module has been
          loaded).</p>
        <p>The following elements will always be present in the list
          for both local and external funs:</p>
        <taglist>
          <tag><c>{type, Type}</c></tag>
          <item>
            <p><c>Type</c> is either <c>local</c> or <c>external</c>.</p>
          </item>
          <tag><c>{module, Module}</c></tag>
          <item>
            <p><c>Module</c> (an atom) is the module name.</p>
            <p>If <c>Fun</c> is a local fun, <c>Module</c> is the module
              in which the fun is defined.</p>
            <p>If <c>Fun</c> is an external fun, <c>Module</c> is the
              module that the fun refers to.</p>
          </item>
          <tag><c>{name, Name}</c></tag>
          <item>
            <p><c>Name</c> (an atom) is a function name.</p>
            <p>If <c>Fun</c> is a local fun, <c>Name</c> is the name
              of the local function that implements the fun.
              (This name was generated by the compiler, and is generally
              only of informational use. As it is a local function, it
              is not possible to call it directly.)
              If no code is currently loaded for the fun, <c>[]</c>
              will be returned instead of an atom.</p>
            <p>If <c>Fun</c> is an external fun, <c>Name</c> is the name
              of the exported function that the fun refers to.</p>
          </item>
          <tag><c>{arity, Arity}</c></tag>
          <item>
            <p><c>Arity</c> is the number of arguments that the fun
              should be called with.</p>
          </item>
          <tag><c>{env, Env}</c></tag>
          <item>
            <p><c>Env</c> (a list) is the environment or free variables
              for the fun. (For external funs, the returned list is
              always empty.)</p>
          </item>
        </taglist>
        <p>The following elements will only be present in the list if
          <c>Fun</c> is local:</p>
        <taglist>
          <tag><c>{pid, Pid}</c></tag>
          <item>
            <p><c>Pid</c> is the pid of the process that originally
              created the fun.</p>
          </item>
          <tag><c>{index, Index}</c></tag>
          <item>
            <p><c>Index</c> (an integer) is an index into the module's
              fun table.</p>
          </item>
          <tag><c>{new_index, Index}</c></tag>
          <item>
            <p><c>Index</c> (an integer) is an index into the module's
              fun table.</p>
          </item>
          <tag><c>{new_uniq, Uniq}</c></tag>
          <item>
            <p><c>Uniq</c> (a binary) is a unique value for this fun.
	    It is calculated from the compiled code for the entire module.</p>
          </item>
          <tag><c>{uniq, Uniq}</c></tag>
          <item>
            <p><c>Uniq</c> (an integer) is a unique value for this fun.
	    Starting in the R15 release, this integer is calculated from
	    the compiled code for the entire module. Before R15, this
	    integer was based on only the body of the fun.
	    </p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="fun_info" arity="2"/>
      <type name="fun_info_item"/>
      <fsummary>Information about a fun</fsummary>
      <desc>
        <p>Returns information about <c><anno>Fun</anno></c> as specified by
          <c><anno>Item</anno></c>, in the form <c>{<anno>Item</anno>,<anno>Info</anno>}</c>.</p>
        <p>For any fun, <c><anno>Item</anno></c> can be any of the atoms
          <c>module</c>, <c>name</c>, <c>arity</c>, <c>env</c>, or <c>type</c>.</p>
        <p>For a local fun, <c><anno>Item</anno></c> can also be any of the atoms
          <c>index</c>, <c>new_index</c>, <c>new_uniq</c>,
          <c>uniq</c>, and <c>pid</c>. For an external fun, the value
          of any of these items is always the atom <c>undefined</c>.</p>
        <p>See
          <seealso marker="#fun_info/1">erlang:fun_info/1</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="fun_to_list" arity="1"/>
      <fsummary>Text representation of a fun</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Fun</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="function_exported" arity="3"/>
      <fsummary>Check if a function is exported and loaded</fsummary>
      <desc>
        <p>Returns <c>true</c> if the module <c><anno>Module</anno></c> is loaded
          and contains an exported function <c><anno>Function</anno>/<anno>Arity</anno></c>,
	  or if there is a BIF (a built-in function implemented in C)
	  with the given name; otherwise returns <c>false</c>.</p>
	  <note><p>This function used to return false for built-in
	  functions before the 18.0 release.</p></note>
      </desc>
    </func>
    <func>
      <name name="garbage_collect" arity="0"/>
      <fsummary>Force an immediate garbage collection of the calling process</fsummary>
      <desc>
        <p>Forces an immediate garbage collection of the currently
          executing process. The function should not be used, unless
          it has been noticed -- or there are good reasons to suspect --
          that the spontaneous garbage collection will occur too late
          or not at all. Improper use may seriously degrade system
          performance.</p>
      </desc>
    </func>
    <func>
      <name name="garbage_collect" arity="1"/>
      <fsummary>Garbage collect a process</fsummary>
      <desc>
        <p>The same as
	<seealso marker="#garbage_collect/2"><c>garbage_collect(<anno>Pid</anno>, [])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="garbage_collect" arity="2"/>
      <fsummary>Garbage collect a process</fsummary>
      <desc>
	<p>Garbage collect the node local process identified by
	<c><anno>Pid</anno></c>.</p>
	<p>Currently available <c><anno>Option</anno></c>s:</p>
        <taglist>
          <tag><c>{async, RequestId}</c></tag>
          <item>
	    The <c>garbage_collect/2</c> function will return
	    the value <c>async</c> immediately after the request
	    has been sent. When the request has been processed, the
	    process that called this function will be passed a
	    message on the form:<br/>
	    <c>{garbage_collect, <anno>RequestId</anno>, <anno>GCResult</anno>}</c>.
	  </item>
        </taglist>
	<p>If <c><anno>Pid</anno></c> equals <c>self()</c>, and
	no <c>async</c> option has been passed, the garbage
	collection will be performed at once, i.e. the same as
	calling
	<seealso marker="#garbage_collect/0">garbage_collect/0</seealso>.
	In all other cases a request for garbage collection will
	be sent to the process identified by <c><anno>Pid</anno></c>,
	and will be handled when appropriate. If no <c>async</c>
	option has been passed, the caller will block until
	<c><anno>GCResult</anno></c> is available and can be
	returned.</p>
	<p><c><anno>GCResult</anno></c> informs about the result of
	the garbage collection request:</p>
        <taglist>
          <tag><c>true</c></tag>
          <item>
	    The process identified by <c><anno>Pid</anno></c> has
	    been garbage collected.
	  </item>
          <tag><c>false</c></tag>
          <item>
	    No garbage collection was performed. This since the
	    the process identified by <c><anno>Pid</anno></c>
	    terminated before the request could be satisfied.
	  </item>
        </taglist>
        <p>Note that the same caveats as for
	<seealso marker="#garbage_collect/0">garbage_collect/0</seealso>
	apply.</p>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>Pid</anno></c> is not a node local process identifier.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>OptionList</anno></c> is not a valid list of options.
	  </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="get" arity="0"/>
      <fsummary>Return the process dictionary</fsummary>
      <desc>
        <p>Returns the process dictionary as a list of
          <c>{<anno>Key</anno>, <anno>Val</anno>}</c> tuples.</p>
        <pre>
> <input>put(key1, merry),</input>
<input>put(key2, lambs),</input>
<input>put(key3, {are, playing}),</input>
<input>get().</input>
[{key1,merry},{key2,lambs},{key3,{are,playing}}]</pre>
      </desc>
    </func>
    <func>
      <name name="get" arity="1"/>
      <fsummary>Return a value from the process dictionary</fsummary>
      <desc>
        <p>Returns the value <c><anno>Val</anno></c> associated with <c><anno>Key</anno></c> in
          the process dictionary, or <c>undefined</c> if <c><anno>Key</anno></c>
          does not exist.</p>
        <pre>
> <input>put(key1, merry),</input>
<input>put(key2, lambs),</input>
<input>put({any, [valid, term]}, {are, playing}),</input>
<input>get({any, [valid, term]}).</input>
{are,playing}</pre>
      </desc>
    </func>
    <func>
      <name name="get_cookie" arity="0"/>
      <fsummary>Get the magic cookie of the local node</fsummary>
      <desc>
        <p>Returns the magic cookie of the local node, if the node is
          alive; otherwise the atom <c>nocookie</c>.</p>
      </desc>
    </func>
    <func>
      <name name="get_keys" arity="0"/>
      <fsummary>Return a list of all keys from the process dictionary</fsummary>
      <desc>
        <p>Returns a list of keys all keys present in the process dictionary.</p>
        <pre>
> <input>put(dog, {animal,1}),</input>
<input>put(cow, {animal,2}),</input>
<input>put(lamb, {animal,3}),</input>
<input>get_keys().</input>
[dog,cow,lamb]</pre>
      </desc>
    </func>
    <func>
      <name name="get_keys" arity="1"/>
      <fsummary>Return a list of keys from the process dictionary</fsummary>
      <desc>
        <p>Returns a list of keys which are associated with the value
          <c><anno>Val</anno></c> in the process dictionary.</p>
        <pre>
> <input>put(mary, {1, 2}),</input>
<input>put(had, {1, 2}),</input>
<input>put(a, {1, 2}),</input>
<input>put(little, {1, 2}),</input>
<input>put(dog, {1, 3}),</input>
<input>put(lamb, {1, 2}),</input>
<input>get_keys({1, 2}).</input>
[mary,had,a,little,lamb]</pre>
      </desc>
    </func>
    <func>
      <name name="get_stacktrace" arity="0"/>
      <fsummary>Get the call stack back-trace of the last exception</fsummary>
      <type name="stack_item"/>
      <desc>
        <p>Get the call stack back-trace (<em>stacktrace</em>) of the last
          exception in the calling process as a list of 
          <c>{<anno>Module</anno>,<anno>Function</anno>,<anno>Arity</anno>,<anno>Location</anno>}</c> tuples.
          The <c><anno>Arity</anno></c> field in the first tuple may be the argument
          list of that function call instead of an arity integer,
          depending on the exception.</p>
        <p>If there has not been any exceptions in a process, the
          stacktrace is <c>[]</c>. After a code change for the process,
          the stacktrace may also be reset to [].</p>
        <p>The stacktrace is the same data as the <c>catch</c> operator
          returns, for example:</p>
        <p><c>{'EXIT',{badarg,Stacktrace}} = catch abs(x)</c></p>
	<p><c><anno>Location</anno></c> is a (possibly empty) list of two-tuples that
	  may indicate the location in the source code of the function.
	  The first element is an atom that describes the type of
	  information in the second element. Currently the following
	  items may occur:</p>
	<taglist>
	  <tag><c>file</c></tag>
	  <item>
	    <p>The second element of the tuple is a string (list of
	      characters) representing the filename of the source file
	      of the function.</p>
	  </item>
	  <tag><c>line</c></tag>
	  <item>
	    <p>The second element of the tuple is the line number
	      (an integer greater than zero) in the source file
	      where the exception occurred or the function was called.</p>
	  </item>
	</taglist>
        <p>See also
          <seealso marker="#error/1">erlang:error/1</seealso> and
          <seealso marker="#error/2">erlang:error/2</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="group_leader" arity="0"/>
      <fsummary>Get the group leader for the calling process</fsummary>
      <desc>
        <p>Returns the pid of the group leader for the process which
          evaluates the function.</p>
        <p>Every process is a member of some process group and all
          groups have a <em>group leader</em>. All IO from the group
          is channeled to the group leader. When a new process is
          spawned, it gets the same group leader as the spawning
          process. Initially, at system start-up, <c>init</c> is both
          its own group leader and the group leader of all processes.</p>
      </desc>
    </func>
    <func>
      <name name="group_leader" arity="2"/>
      <fsummary>Set the group leader for a process</fsummary>
      <desc>
        <p>Sets the group leader of <c><anno>Pid</anno></c> to <c><anno>GroupLeader</anno></c>.
          Typically, this is used when a processes started from a
          certain shell should have another group leader than
          <c>init</c>.</p>
        <p>See also
          <seealso marker="#group_leader/0">group_leader/0</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="halt" arity="0"/>
      <fsummary>Halt the Erlang runtime system and indicate normal exit to the calling environment</fsummary>
      <desc>
	<p>The same as
	  <seealso marker="#halt/2"><c>halt(0, [])</c></seealso>.</p>
        <pre>
> <input>halt().</input>
os_prompt% </pre>
      </desc>
    </func>
    <func>
      <name name="halt" arity="1"/>
      <fsummary>Halt the Erlang runtime system</fsummary>
      <desc>
	<p>The same as
	  <seealso marker="#halt/2"><c>halt(<anno>Status</anno>, [])</c></seealso>.</p>
        <pre>
> <input>halt(17).</input>
os_prompt% <input>echo $?</input>
17
os_prompt% </pre>
      </desc>
    </func>
    <func>
      <name name="halt" arity="2"/>
      <fsummary>Halt the Erlang runtime system</fsummary>
      <desc>
        <p><c><anno>Status</anno></c> must be a non-negative integer, a string,
	  or the atom <c>abort</c>.
	  Halts the Erlang runtime system. Has no return value.
	  Depending on <c><anno>Status</anno></c>:
	</p>
	<taglist>
	  <tag>integer()</tag>
	  <item>The runtime system exits with the integer value <c><anno>Status</anno></c>
	  as status code to the calling environment (operating system).
	  </item>
	  <tag>string()</tag>
	  <item>An erlang crash dump is produced with <c><anno>Status</anno></c> as slogan,
	  and then the runtime system exits with status code <c>1</c>.
	  </item>
	  <tag><c>abort</c></tag>
	  <item>
	    The runtime system aborts producing a core dump, if that is
	    enabled in the operating system.
	  </item>
	</taglist>
	<p>Note that on many platforms, only the status codes 0-255 are
	  supported by the operating system.
	</p>
	<p>For integer <c><anno>Status</anno></c> the Erlang runtime system closes all ports
	  and allows async threads to finish their operations before exiting.
	  To exit without such flushing use
	  <c><anno>Option</anno></c> as <c>{flush,false}</c>.
	</p>
	<p>For statuses <c>string()</c> and <c>abort</c> the <c>flush</c>
	  option is ignored and flushing is <em>not</em> done.
	</p>
      </desc>
    </func>
    <func>
      <name name="hash" arity="2"/>
      <fsummary>Hash function (deprecated)</fsummary>
      <desc>
        <p>Returns a hash value for <c><anno>Term</anno></c> within the range
          <c>1..<anno>Range</anno></c>. The allowed range is 1..2^27-1.</p>
        <warning>
          <p>This BIF is deprecated as the hash value may differ on
            different architectures. Also the hash values for integer
            terms larger than 2^27 as well as large binaries are very
            poor. The BIF is retained for backward compatibility
            reasons (it may have been used to hash records into a file),
            but all new code should use one of the BIFs
            <c>erlang:phash/2</c> or <c>erlang:phash2/1,2</c> instead.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="hd" arity="1"/>
      <fsummary>Head of a list</fsummary>
      <desc>
        <p>Returns the head of <c><anno>List</anno></c>, that is, the first element.</p>
        <pre>
> <input>hd([1,2,3,4,5]).</input>
1</pre>
        <p>Allowed in guard tests.</p>
        <p>Failure: <c>badarg</c> if <c><anno>List</anno></c> is the empty list [].</p>
      </desc>
    </func>
    <func>
      <name name="hibernate" arity="3"/>
      <fsummary>Hibernate a process until a message is sent to it</fsummary>
      <desc>
        <p>Puts the calling process into a wait state where its memory
          allocation has been reduced as much as possible, which is
          useful if the process does not expect to receive any messages
          in the near future.</p>
        <p>The process will be awaken when a message is sent to it, and
          control will resume in <c><anno>Module</anno>:<anno>Function</anno></c> with
          the arguments given by <c><anno>Args</anno></c> with the call stack
          emptied, meaning that the process will terminate when that
          function returns. Thus <c>erlang:hibernate/3</c> will never
          return to its caller.</p>
        <p>If the process has any message in its message queue,
          the process will be awaken immediately in the same way as
          described above.</p>
        <p>In more technical terms, what <c>erlang:hibernate/3</c> does
          is the following. It discards the call stack for the process.
          Then it garbage collects the process. After the garbage
          collection, all live data is in one continuous heap. The heap
          is then shrunken to the exact same size as the live data
          which it holds (even if that size is less than the minimum
          heap size for the process).</p>
        <p>If the size of the live data in the process is less than
          the minimum heap size, the first garbage collection occurring
          after the process has been awaken will ensure that the heap
          size is changed to a size not smaller than the minimum heap
          size.</p>
        <p>Note that emptying the call stack means that any surrounding
          <c>catch</c> is removed and has to be re-inserted after
          hibernation. One effect of this is that processes started
          using <c>proc_lib</c> (also indirectly, such as
          <c>gen_server</c> processes), should use
          <seealso marker="stdlib:proc_lib#hibernate/3">proc_lib:hibernate/3</seealso>
          instead to ensure that the exception handler continues to work
          when the process wakes up.</p>
      </desc>
    </func>

    <func>
      <name name="insert_element" arity="3"/>
      <fsummary>Insert an element at index in a tuple</fsummary>
      <type_desc variable="Index">1..tuple_size(<anno>Tuple1</anno>) + 1</type_desc>
      <desc>
		  <p>
			  Returns a new tuple with element <c><anno>Term</anno></c> insert at position
			  <c><anno>Index</anno></c> in tuple <c><anno>Tuple1</anno></c>.
			  All elements from position <c><anno>Index</anno></c> and upwards are subsequently
			  pushed one step higher in the new tuple <c><anno>Tuple2</anno></c>.
		  </p>
        <pre>
> <input>erlang:insert_element(2, {one, two, three}, new).</input>
{one,new,two,three}</pre>
      </desc>
    </func>
    <func>
      <name name="integer_to_binary" arity="1"/>
      <fsummary>Text representation of an integer</fsummary>
      <desc>
        <p>Returns a binary which corresponds to the text
          representation of <c><anno>Integer</anno></c>.</p>
        <pre>
> <input>integer_to_binary(77).</input>
&lt;&lt;"77">></pre>
      </desc>
    </func>
    <func>
      <name name="integer_to_binary" arity="2"/>
      <fsummary>Text representation of an integer</fsummary>
      <desc>
        <p>Returns a binary which corresponds to the text
          representation of <c><anno>Integer</anno></c> in base <c><anno>Base</anno></c>.</p>
        <pre>
> <input>integer_to_binary(1023, 16).</input>
&lt;&lt;"3FF">></pre>
      </desc>
    </func>
    <func>
      <name name="integer_to_list" arity="1"/>
      <fsummary>Text representation of an integer</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Integer</anno></c>.</p>
        <pre>
> <input>integer_to_list(77).</input>
"77"</pre>
      </desc>
    </func>
    <func>
      <name name="integer_to_list" arity="2"/>
      <fsummary>Text representation of an integer</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Integer</anno></c> in base <c><anno>Base</anno></c>.</p>
        <pre>
> <input>integer_to_list(1023, 16).</input>
"3FF"</pre>
      </desc>
    </func>
    <func>
      <name name="iolist_to_binary" arity="1"/>
      <fsummary>Convert an iolist to a binary</fsummary>
      <desc>
        <p>Returns a binary which is made from the integers and
          binaries in <c><anno>IoListOrBinary</anno></c>.</p>
        <pre>
> <input>Bin1 = &lt;&lt;1,2,3&gt;&gt;.</input>
&lt;&lt;1,2,3&gt;&gt;
> <input>Bin2 = &lt;&lt;4,5&gt;&gt;.</input>
&lt;&lt;4,5&gt;&gt;
> <input>Bin3 = &lt;&lt;6&gt;&gt;.</input>
&lt;&lt;6&gt;&gt;
> <input>iolist_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).</input>
&lt;&lt;1,2,3,1,2,3,4,5,4,6&gt;&gt;</pre>
      </desc>
    </func>
    <func>
      <name name="iolist_size" arity="1"/>
      <fsummary>Size of an iolist</fsummary>
      <desc>
        <p>Returns an integer which is the size in bytes
          of the binary that would be the result of 
          <c>iolist_to_binary(<anno>Item</anno>)</c>.</p>
        <pre>
> <input>iolist_size([1,2|&lt;&lt;3,4>>]).</input>
4</pre>
      </desc>
    </func>
    <func>
      <name name="is_alive" arity="0"/>
      <fsummary>Check whether the local node is alive</fsummary>
      <desc>
        <p>Returns <c>true</c> if the local node is alive; that is, if
          the node can be part of a distributed system. Otherwise, it
          returns <c>false</c>.</p>
      </desc>
    </func>
    <func>
      <name name="is_atom" arity="1"/>
      <fsummary>Check whether a term is an atom</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is an atom;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_binary" arity="1"/>
      <fsummary>Check whether a term is a binary</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a binary;
          otherwise returns <c>false</c>.</p>

	<p>A binary always contains a complete number of bytes.</p>

        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_bitstring" arity="1"/>
      <fsummary>Check whether a term is a bitstring</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a bitstring (including a binary);
          otherwise returns <c>false</c>.</p>

        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_boolean" arity="1"/>
      <fsummary>Check whether a term is a boolean</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is
          either the atom <c>true</c> or the atom <c>false</c>
          (i.e. a boolean); otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_builtin" arity="3"/>
      <fsummary>Check if a function is a BIF implemented in C</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Module</anno>:<anno>Function</anno>/<anno>Arity</anno></c> is
          a BIF implemented in C; otherwise returns <c>false</c>.
          This BIF is useful for builders of cross reference tools.</p>
      </desc>
    </func>
    <func>
      <name name="is_float" arity="1"/>
      <fsummary>Check whether a term is a float</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a floating point
          number; otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_function" arity="1"/>
      <fsummary>Check whether a term is a fun</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a fun; otherwise
          returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_function" arity="2"/>
      <fsummary>Check whether a term is a fun with a given arity</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a fun that can be
          applied with <c><anno>Arity</anno></c> number of arguments; otherwise
          returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_integer" arity="1"/>
      <fsummary>Check whether a term is an integer</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is an integer;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_list" arity="1"/>
      <fsummary>Check whether a term is a list</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a list with
          zero or more elements; otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_map" arity="1"/>
      <fsummary>Check whether a term is a map</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a map;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_number" arity="1"/>
      <fsummary>Check whether a term is a number</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is either an integer or a
          floating point number; otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_pid" arity="1"/>
      <fsummary>Check whether a term is a pid</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a pid (process
          identifier); otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_port" arity="1"/>
      <fsummary>Check whether a term is a port</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a port identifier;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_process_alive" arity="1"/>
      <fsummary>Check whether a process is alive</fsummary>
      <desc>
        <p>
	  <c><anno>Pid</anno></c> must refer to a process at the local node.
          Returns <c>true</c> if the process exists and is alive, that
          is, is not exiting and has not exited. Otherwise, returns
	  <c>false</c>.
	</p>
      </desc>
    </func>
    <func>
      <name name="is_record" arity="2"/>
      <fsummary>Check whether a term appears to be a record</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a tuple and its first
          element is <c><anno>RecordTag</anno></c>. Otherwise, returns <c>false</c>.</p>
        <note>
          <p>Normally the compiler treats calls to <c>is_record/2</c>
            specially. It emits code to verify that <c><anno>Term</anno></c> is a
            tuple, that its first element is <c><anno>RecordTag</anno></c>, and that
            the size is correct. However, if the <c><anno>RecordTag</anno></c> is
            not a literal atom, the <c>is_record/2</c> BIF will be
            called instead and the size of the tuple will not be
            verified.</p>
        </note>
        <p>Allowed in guard tests, if <c><anno>RecordTag</anno></c> is a literal
          atom.</p>
      </desc>
    </func>
    <func>
      <name name="is_record" arity="3"/>
      <fsummary>Check whether a term appears to be a record</fsummary>
      <desc>
        <p><c><anno>RecordTag</anno></c> must be an atom. Returns <c>true</c> if
          <c><anno>Term</anno></c> is a tuple, its first element is <c><anno>RecordTag</anno></c>,
          and its size is <c><anno>Size</anno></c>. Otherwise, returns <c>false</c>.</p>
        <p>Allowed in guard tests, provided that <c><anno>RecordTag</anno></c> is
          a literal atom and <c>Size</c> is a literal integer.</p>
        <note>
          <p>This BIF is documented for completeness. In most cases
            <c>is_record/2</c> should be used.</p>
        </note>
      </desc>
    </func>
    <func>
      <name name="is_reference" arity="1"/>
      <fsummary>Check whether a term is a reference</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a reference;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="is_tuple" arity="1"/>
      <fsummary>Check whether a term is a tuple</fsummary>
      <desc>
        <p>Returns <c>true</c> if <c><anno>Term</anno></c> is a tuple;
          otherwise returns <c>false</c>.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="length" arity="1"/>
      <fsummary>Length of a list</fsummary>
      <desc>
        <p>Returns the length of <c><anno>List</anno></c>.</p>
        <pre>
> <input>length([1,2,3,4,5,6,7,8,9]).</input>
9</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="link" arity="1"/>
      <fsummary>Create a link to another process (or port)</fsummary>
      <desc>
        <p>Creates a link between the calling process and another
          process (or port) <c><anno>PidOrPort</anno></c>, if there is not such a link
          already. If a process attempts to create a link to itself,
          nothing is done. Returns <c>true</c>.</p>
        <p>If <c><anno>PidOrPort</anno></c> does not exist, the behavior of the BIF depends
          on if the calling process is trapping exits or not (see
          <seealso marker="#process_flag/2">process_flag/2</seealso>):</p>
        <list type="bulleted">
          <item>If the calling process is not trapping exits, and
           checking <c><anno>PidOrPort</anno></c> is cheap -- that is, if <c><anno>PidOrPort</anno></c> is
           local -- <c>link/1</c> fails with reason <c>noproc</c>.</item>
          <item>Otherwise, if the calling process is trapping exits,
           and/or <c><anno>PidOrPort</anno></c> is remote, <c>link/1</c> returns
          <c>true</c>, but an exit signal with reason <c>noproc</c>
           is sent to the calling process.</item>
        </list>
      </desc>
    </func>
    <func>
      <name name="list_to_atom" arity="1"/>
      <fsummary>Convert from text representation to an atom</fsummary>
      <desc>
        <p>Returns the atom whose text representation is <c><anno>String</anno></c>.</p>
	<p><c><anno>String</anno></c> may only contain ISO-latin-1
	characters (i.e. numbers below 256) as the current
	implementation does not allow unicode characters >= 256 in
	atoms. For more information on Unicode support in atoms
	see <seealso marker="erl_ext_dist#utf8_atoms">note on UTF-8 encoded atoms</seealso>
	in the chapter about the external term format in the ERTS User's Guide.</p>
        <pre>
> <input>list_to_atom("Erlang").</input>
'Erlang'</pre>
      </desc>
    </func>
    <func>
      <name name="list_to_binary" arity="1"/>
      <fsummary>Convert a list to a binary</fsummary>
      <desc>
        <p>Returns a binary which is made from the integers and
          binaries in <c><anno>IoList</anno></c>.</p>
        <pre>
> <input>Bin1 = &lt;&lt;1,2,3&gt;&gt;.</input>
&lt;&lt;1,2,3&gt;&gt;
> <input>Bin2 = &lt;&lt;4,5&gt;&gt;.</input>
&lt;&lt;4,5&gt;&gt;
> <input>Bin3 = &lt;&lt;6&gt;&gt;.</input>
&lt;&lt;6&gt;&gt;
> <input>list_to_binary([Bin1,1,[2,3,Bin2],4|Bin3]).</input>
&lt;&lt;1,2,3,1,2,3,4,5,4,6&gt;&gt;</pre>
      </desc>
    </func>
    <func>
      <name name="list_to_bitstring" arity="1"/>
      <type name="bitstring_list"/>
      <fsummary>Convert a list to a bitstring</fsummary>
      <desc>
        <p>Returns a bitstring which is made from the integers and
          bitstrings in <c><anno>BitstringList</anno></c>. (The last tail in <c><anno>BitstringList</anno></c>
	  is allowed to be a bitstring.)</p>
        <pre>
> <input>Bin1 = &lt;&lt;1,2,3&gt;&gt;.</input>
&lt;&lt;1,2,3&gt;&gt;
> <input>Bin2 = &lt;&lt;4,5&gt;&gt;.</input>
&lt;&lt;4,5&gt;&gt;
> <input>Bin3 = &lt;&lt;6,7:4,&gt;&gt;.</input>
&lt;&lt;6&gt;&gt;
> <input>list_to_bitstring([Bin1,1,[2,3,Bin2],4|Bin3]).</input>
&lt;&lt;1,2,3,1,2,3,4,5,4,6,7:46&gt;&gt;</pre>
      </desc>
    </func>
    <func>
      <name name="list_to_existing_atom" arity="1"/>
      <fsummary>Convert from text representation to an atom</fsummary>
      <desc>
        <p>Returns the atom whose text representation is <c><anno>String</anno></c>,
          but only if there already exists such atom.</p>
        <p>Failure: <c>badarg</c> if there does not already exist an atom
          whose text representation is <c><anno>String</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="list_to_float" arity="1"/>
      <fsummary>Convert from text representation to a float</fsummary>
      <desc>
        <p>Returns the float whose text representation is <c><anno>String</anno></c>.</p>
        <pre>
> <input>list_to_float("2.2017764e+0").</input>
2.2017764</pre>
        <p>Failure: <c>badarg</c> if <c><anno>String</anno></c> contains a bad
          representation of a float.</p>
      </desc>
    </func>
    <func>
      <name name="list_to_integer" arity="1"/>
      <fsummary>Convert from text representation to an integer</fsummary>
      <desc>
        <p>Returns an integer whose text representation is
          <c><anno>String</anno></c>.</p>
        <pre>
> <input>list_to_integer("123").</input>
123</pre>
        <p>Failure: <c>badarg</c> if <c><anno>String</anno></c> contains a bad
          representation of an integer.</p>
      </desc>
    </func>
    <func>
      <name name="list_to_integer" arity="2"/>
      <fsummary>Convert from text representation to an integer</fsummary>
      <desc>
        <p>Returns an integer whose text representation in base
          <c><anno>Base</anno></c> is <c><anno>String</anno></c>.</p>
        <pre>
> <input>list_to_integer("3FF", 16).</input>
1023</pre>
        <p>Failure: <c>badarg</c> if <c><anno>String</anno></c> contains a bad
          representation of an integer.</p>
      </desc>
    </func>
    <func>
      <name name="list_to_pid" arity="1"/>
      <fsummary>Convert from text representation to a pid</fsummary>
      <desc>
        <p>Returns a pid whose text representation is <c><anno>String</anno></c>.</p>
        <warning>
          <p>This BIF is intended for debugging and for use in
            the Erlang operating system. It should not be used in
            application programs.</p>
        </warning>
        <pre>
> <input>list_to_pid("&lt;0.4.1>").</input>
&lt;0.4.1></pre>
        <p>Failure: <c>badarg</c> if <c><anno>String</anno></c> contains a bad
          representation of a pid.</p>
      </desc>
    </func>
    <func>
      <name name="list_to_tuple" arity="1"/>
      <fsummary>Convert a list to a tuple</fsummary>
      <desc>
        <p>Returns a tuple which corresponds to <c><anno>List</anno></c>. <c><anno>List</anno></c>
          can contain any Erlang terms.</p>
        <pre>
> <input>list_to_tuple([share, ['Ericsson_B', 163]]).</input>
{share, ['Ericsson_B', 163]}</pre>
      </desc>
    </func>
    <func>
      <name name="load_module" arity="2"/>
      <fsummary>Load object code for a module</fsummary>
      <desc>
        <p>If <c><anno>Binary</anno></c> contains the object code for the module
          <c><anno>Module</anno></c>, this BIF loads that object code. Also, if
          the code for the module <c><anno>Module</anno></c> already exists, all
          export references are replaced so they point to the newly
          loaded code. The previously loaded code is kept in the system
          as old code, as there may still be processes which are
          executing that code. It returns either
          <c>{module, <anno>Module</anno>}</c>, or <c>{error, <anno>Reason</anno>}</c> if loading
          fails. <c><anno>Reason</anno></c> is one of the following:</p>
        <taglist>
          <tag><c>badfile</c></tag>
          <item>
            <p>The object code in <c><anno>Binary</anno></c> has an
              incorrect format <em>or</em> the object code contains code
              for another module than <c><anno>Module</anno></c>.</p>
          </item>
          <tag><c>not_purged</c></tag>
          <item>
            <p><c><anno>Binary</anno></c> contains a module which cannot be loaded
              because old code for this module already exists.</p>
          </item>
        </taglist>
        <warning>
          <p>This BIF is intended for the code server (see
            <seealso marker="kernel:code">code(3)</seealso>) and should not be
            used elsewhere.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="load_nif" arity="2"/>
      <fsummary>Load NIF library</fsummary>
      <desc>
        <note>
          <p>In releases older than OTP R14B, NIFs were an
          experimental feature. Versions of OTP older than R14B might
          have different and possibly incompatible NIF semantics and
          interfaces. For example, in R13B03 the return value on
          failure was
          <c>{error,Reason,Text}</c>.</p>
        </note>
        <p>Loads and links a dynamic library containing native
        implemented functions (NIFs) for a module. <c><anno>Path</anno></c> is a
        file path to the sharable object/dynamic library file minus
        the OS-dependent file extension (.so for Unix and .dll for
        Windows). See <seealso marker="erl_nif">erl_nif</seealso>
        on how to implement a NIF library.</p> 
        <p><c><anno>LoadInfo</anno></c> can be any term. It will be passed on to
        the library as part of the initialization. A good practice is
        to include a module version number to support future code
        upgrade scenarios.</p>
        <p>The call to <c>load_nif/2</c> must be made
        <em>directly</em> from the Erlang code of the module that the
        NIF library belongs to.</p>
        <p>It returns either <c>ok</c>, or <c>{error,{<anno>Reason</anno>,Text}}</c>
        if loading fails. <c><anno>Reason</anno></c> is one of the atoms below,
        while <c><anno>Text</anno></c> is a human readable string that may give
        some more information about the failure.</p>
        <taglist>
          <tag><c>load_failed</c></tag>
          <item>
            <p>The OS failed to load the NIF library.</p>
          </item>
          <tag><c>bad_lib</c></tag>
          <item>
            <p>The library did not fulfil the requirements as a NIF
            library of the calling module.</p> 
          </item>
          <tag><c>load | reload | upgrade</c></tag>
          <item>
            <p>The corresponding library callback was not successful.</p>
          </item>
          <tag><c>old_code</c></tag>
          <item>
            <p>The call to <c>load_nif/2</c> was made from the old
            code of a module that has been upgraded. This is not
            allowed.</p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="loaded" arity="0"/>
      <fsummary>List of all loaded modules</fsummary>
      <desc>
        <p>Returns a list of all loaded Erlang modules (current and/or
          old code), including preloaded modules.</p>
        <p>See also <seealso marker="kernel:code">code(3)</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="localtime" arity="0"/>
      <fsummary>Current local date and time</fsummary>
      <desc>
        <p>Returns the current local date and time
          <c>{{Year, Month, Day}, {Hour, Minute, Second}}</c>.</p>
        <p>The time zone and daylight saving time correction depend
          on the underlying OS.</p>
        <pre>
> <input>erlang:localtime().</input>
{{1996,11,6},{14,45,17}}</pre>
      </desc>
    </func>
    <func>
      <name name="localtime_to_universaltime" arity="1"/>
      <fsummary>Convert from local to Universal Time Coordinated (UTC) date and time</fsummary>
      <desc>
        <p>Converts local date and time to Universal Time Coordinated
          (UTC), if this is supported by the underlying OS. Otherwise,
          no conversion is done and <c><anno>Localtime</anno></c> is returned.</p>
        <pre>
> <input>erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}).</input>
{{1996,11,6},{13,45,17}}</pre>
        <p>Failure: <c>badarg</c> if <c><anno>Localtime</anno></c> does not denote
          a valid date and time.</p>
      </desc>
    </func>
    <func>
      <name name="localtime_to_universaltime" arity="2"/>
      <fsummary>Convert from local to Universal Time Coordinated (UTC) date and time</fsummary>
      <desc>
        <p>Converts local date and time to Universal Time Coordinated
          (UTC) just like <c>erlang:localtime_to_universaltime/1</c>,
          but the caller decides if daylight saving time is active or
          not.</p>
        <p>If <c><anno>IsDst</anno> == true</c> the <c><anno>Localtime</anno></c> is during
          daylight saving time, if <c><anno>IsDst</anno> == false</c> it is not,
          and if <c><anno>IsDst</anno> == undefined</c> the underlying OS may
          guess, which is the same as calling
          <c>erlang:localtime_to_universaltime(<anno>Localtime</anno>)</c>.</p>
        <pre>
> <input>erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, true).</input>
{{1996,11,6},{12,45,17}}
> <input>erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, false).</input>
{{1996,11,6},{13,45,17}}
> <input>erlang:localtime_to_universaltime({{1996,11,6},{14,45,17}}, undefined).</input>
{{1996,11,6},{13,45,17}}</pre>
        <p>Failure: <c>badarg</c> if <c><anno>Localtime</anno></c> does not denote
          a valid date and time.</p>
      </desc>
    </func>
    <func>
      <name name="make_ref" arity="0"/>
      <fsummary>Return a unique reference</fsummary>
      <desc>
	<p>Return a <seealso marker="doc/efficiency_guide:advanced#unique_references">unique
	reference</seealso>. The reference is unique among
	connected nodes.</p>
	<warning><p>Known issue: When a node is restarted multiple
	times with the same node name, references created
	on a newer node can be mistaken for a reference
	created on an older node with the same node name.</p></warning>
      </desc>
    </func>
    <func>
      <name name="make_tuple" arity="2"/>
      <fsummary>Create a new tuple of a given arity</fsummary>
      <desc>
        <p>Returns a new tuple of the given <c><anno>Arity</anno></c>, where all
          elements are <c><anno>InitialValue</anno></c>.</p>
        <pre>
> <input>erlang:make_tuple(4, []).</input>
{[],[],[],[]}</pre>
      </desc>
    </func>
    <func>
      <name name="make_tuple" arity="3"/>
      <fsummary>Create a new tuple with given arity and contents</fsummary>
      <desc>
        <p><c>erlang:make_tuple</c> first creates a tuple of size <c><anno>Arity</anno></c>
	  where each element has the value <c><anno>DefaultValue</anno></c>. It then fills
	  in values from <c><anno>InitList</anno></c>. Each list element in <c><anno>InitList</anno></c>
	  must be a two-tuple where the first element is a position in the
	  newly created tuple and the second element is any term. If a position
	  occurs more than once in the list, the term corresponding to
	  last occurrence will be used.</p>
        <pre>
> <input>erlang:make_tuple(5, [], [{2,ignored},{5,zz},{2,aa}]).</input>
{{[],aa,[],[],zz}</pre>
      </desc>
    </func>
    <func>
      <name name="map_size" arity="1"/>
      <fsummary>Return the size of a map</fsummary>
      <desc>
        <p>Returns an integer which is the number of key-value pairs in <c><anno>Map</anno></c>.</p>
        <pre>
> <input>map_size(#{a=>1, b=>2, c=>3}).</input>
3</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="max" arity="2"/>
      <fsummary>Return the largest of two term</fsummary>
      <desc>
        <p>Return the largest of <c><anno>Term1</anno></c> and <c><anno>Term2</anno></c>;
	if the terms compare equal, <c><anno>Term1</anno></c> will be returned.</p>
      </desc>
    </func>
    <func>
      <name name="md5" arity="1"/>
      <fsummary>Compute an MD5 message digest</fsummary>
      <desc>
        <p>Computes an <c>MD5</c> message digest from <c><anno>Data</anno></c>, where
          the length of the digest is 128 bits (16 bytes). <c><anno>Data</anno></c>
          is a binary or a list of small integers and binaries.</p>
        <p>See The MD5 Message Digest Algorithm (RFC 1321) for more
          information about MD5.</p>
	<warning><p>The MD5 Message Digest Algorithm is <em>not</em> considered
	safe for code-signing or software integrity purposes.</p></warning>
      </desc>
    </func>
    <func>
      <name name="md5_final" arity="1"/>
      <fsummary>Finish the update of an MD5 context and return the computed MD5 message digest</fsummary>
      <desc>
        <p>Finishes the update of an MD5 <c><anno>Context</anno></c> and returns
          the computed <c>MD5</c> message digest.</p>
      </desc>
    </func>
    <func>
      <name name="md5_init" arity="0"/>
      <fsummary>Create an MD5 context</fsummary>
      <desc>
        <p>Creates an MD5 context, to be used in subsequent calls to
          <c>md5_update/2</c>.</p>
      </desc>
    </func>
    <func>
      <name name="md5_update" arity="2"/>
      <fsummary>Update an MD5 context with data, and return a new context</fsummary>
      <desc>
        <p>Updates an MD5 <c><anno>Context</anno></c> with <c><anno>Data</anno></c>, and returns
          a <c><anno>NewContext</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="memory" arity="0"/>
      <type name="memory_type"/>
      <fsummary>Information about dynamically allocated memory</fsummary>
      <desc>
        <p>Returns a list containing information about memory
          dynamically allocated by the Erlang emulator. Each element of
          the list is a tuple <c>{Type, Size}</c>. The first element
          <c><anno>Type</anno></c>is an atom describing memory type. The second
          element <c><anno>Size</anno></c>is memory size in bytes. A description of
          each memory type follows:</p>
        <taglist>
          <tag><c>total</c></tag>
          <item>
            <p>The total amount of memory currently allocated, which is
              the same as the sum of memory size for <c>processes</c>
              and <c>system</c>.</p>
          </item>
          <tag><c>processes</c></tag>
          <item>
            <p>The total amount of memory currently allocated by
              the Erlang processes.</p>
          </item>
          <tag><c>processes_used</c></tag>
          <item>
            <p>The total amount of memory currently used by the Erlang
              processes.</p>
            <p>This memory is part of the memory presented as
              <c>processes</c> memory.</p>
          </item>
          <tag><c>system</c></tag>
          <item>
            <p>The total amount of memory currently allocated by
              the emulator that is not directly related to any Erlang
              process.</p>
            <p>Memory presented as <c>processes</c> is not included in
              this memory.</p>
          </item>
          <tag><c>atom</c></tag>
          <item>
            <p>The total amount of memory currently allocated for atoms.</p>
            <p>This memory is part of the memory presented as
              <c>system</c> memory.</p>
          </item>
          <tag><c>atom_used</c></tag>
          <item>
            <p>The total amount of memory currently used for atoms.</p>
            <p>This memory is part of the memory presented as
              <c>atom</c> memory.</p>
          </item>
          <tag><c>binary</c></tag>
          <item>
            <p>The total amount of memory currently allocated for
              binaries.</p>
            <p>This memory is part of the memory presented as
              <c>system</c> memory.</p>
          </item>
          <tag><c>code</c></tag>
          <item>
            <p>The total amount of memory currently allocated for
              Erlang code.</p>
            <p>This memory is part of the memory presented as
              <c>system</c> memory.</p>
          </item>
          <tag><c>ets</c></tag>
          <item>
            <p>The total amount of memory currently allocated for ets
              tables.</p>
            <p>This memory is part of the memory presented as
              <c>system</c> memory.</p>
          </item>
          <tag><c>low</c></tag>
          <item>
            <p>Only on 64-bit halfword emulator.</p>
            <p>The total amount of memory allocated in low memory areas
	      that are restricted to less than 4 Gb even though
	      the system may have more physical memory.</p>
	    <p>May be removed in future releases of halfword emulator.</p>
          </item>
          <tag><c>maximum</c></tag>
          <item>
            <p>The maximum total amount of memory allocated since
              the emulator was started.</p>
            <p>This tuple is only present when the emulator is run with
              instrumentation.</p>
            <p>For information on how to run the emulator with
              instrumentation see
              <seealso marker="tools:instrument">instrument(3)</seealso>
              and/or <seealso marker="erts:erl">erl(1)</seealso>.</p>
          </item>
        </taglist>
        <note>
          <p>The <c>system</c> value is not complete. Some allocated
            memory that should be part of the <c>system</c> value are
            not.</p>
          <p>When the emulator is run with instrumentation,
            the <c>system</c> value is more accurate, but memory
            directly allocated by <c>malloc</c> (and friends) are still
            not part of the <c>system</c> value. Direct calls to
            <c>malloc</c> are only done from OS specific runtime
            libraries and perhaps from user implemented Erlang drivers
            that do not use the memory allocation functions in
            the driver interface.</p>
          <p>Since the <c>total</c> value is the sum of <c>processes</c>
            and <c>system</c> the error in <c>system</c> will propagate
            to the <c>total</c> value.</p>
	  <p>The different amounts of memory that are summed are
	    <em>not</em> gathered atomically which also introduce
	    an error in the result.</p>
        </note>
        <p>The different values has the following relation to each
          other. Values beginning with an uppercase letter is not part
          of the result.</p>
        <code type="none">
        total = processes + system
        processes = processes_used + ProcessesNotUsed
        system = atom + binary + code + ets + OtherSystem
        atom = atom_used + AtomNotUsed

        RealTotal = processes + RealSystem
        RealSystem = system + MissedSystem</code>
        <p>More tuples in the returned list may be added in the future.</p>
        <note>
          <p>The <c>total</c> value is supposed to be the total amount
            of memory dynamically allocated by the emulator. Shared
            libraries, the code of the emulator itself, and
            the emulator stack(s) are not supposed to be included. That
            is, the <c>total</c> value is <em>not</em> supposed to be
            equal to the total size of all pages mapped to the emulator.
            Furthermore, due to fragmentation and pre-reservation of
            memory areas, the size of the memory segments which contain
            the dynamically allocated memory blocks can be substantially
            larger than the total size of the dynamically allocated
            memory blocks.</p>
        </note>
	<note>
	  <p>
	    Since erts version 5.6.4 <c>erlang:memory/0</c> requires that
	    all <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>
	    allocators are enabled (default behaviour).
	  </p>
	</note>
        <p>Failure:</p>
        <taglist>
          <tag><c>notsup</c></tag>
          <item>
	    If an <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>
	    allocator has been disabled.
	  </item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="memory" arity="1" clause_i="1"/>
      <name name="memory" arity="1" clause_i="2"/>
      <type name="memory_type"/>
      <fsummary>Information about dynamically allocated memory</fsummary>
      <desc>
        <p>Returns the memory size in bytes allocated for memory of
          type <c><anno>Type</anno></c>. The argument can also be given as a list
          of <c>memory_type()</c> atoms, in which case a corresponding list of
          <c>{memory_type(), Size :: integer >= 0}</c> tuples is returned.</p>
	<note>
	  <p>
	    Since erts version 5.6.4 <c>erlang:memory/1</c> requires that
	    all <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>
	    allocators are enabled (default behaviour).
	  </p>
	</note>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>Type</anno></c> is not one of the memory types listed in the
	    documentation of
	    <seealso marker="#memory/0">erlang:memory/0</seealso>.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	    If <c>maximum</c> is passed as <c><anno>Type</anno></c> and the emulator
	    is not run in instrumented mode.
	  </item>
          <tag><c>notsup</c></tag>
          <item>
	    If an <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>
	    allocator has been disabled.
	  </item>
	</taglist>
        <p>See also
          <seealso marker="#memory/0">erlang:memory/0</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="min" arity="2"/>
      <fsummary>Return the smallest of two term</fsummary>
      <desc>
        <p>Return the smallest of <c><anno>Term1</anno></c> and <c><anno>Term2</anno></c>;
	if the terms compare equal, <c><anno>Term1</anno></c> will be returned.</p>
      </desc>
    </func>
    <func>
      <name name="module_loaded" arity="1"/>
      <fsummary>Check if a module is loaded</fsummary>
      <desc>
        <p>Returns <c>true</c> if the module <c><anno>Module</anno></c> is loaded,
          otherwise returns <c>false</c>. It does not attempt to load
          the module.</p>
        <warning>
          <p>This BIF is intended for the code server (see
            <seealso marker="kernel:code">code(3)</seealso>) and should not be
            used elsewhere.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="monitor" arity="2" clause_i="1"/>
      <name name="monitor" arity="2" clause_i="2"/>
      <type name="registered_name"/>
      <type name="registered_process_identifier"/>
      <type name="monitor_process_identifier"/>
      <fsummary>Start monitoring</fsummary>
      <desc>
	<p>Send a monitor request of type <c><anno>Type</anno></c> to the
	entity identified by <c><anno>Item</anno></c>. The caller of
	<c>monitor/2</c> will later be notified by a monitor message on the
	following format if the monitored state is changed:</p>
        <code type="none">{Tag, <anno>MonitorRef</anno>, <anno>Type</anno>, Object, Info}</code>
	<note><p>The monitor request is an asynchronous signal. That is, it
	takes time before the signal reach its destination.</p></note>
	<p>Currently valid <c><anno>Type</anno></c>s:</p>
	<taglist>
	  <tag><marker id="monitor_process"/><c>process</c></tag>
	  <item>
	    <p>Monitor the existence of the process identified by
	    <c><anno>Item</anno></c>. Currently valid
	    <c><anno>Item</anno></c>s in combination with the
	    <c>process <anno>Type</anno></c>:</p>
            <taglist>
              <tag><c>pid()</c></tag>
              <item>
		<p>The process identifier of the process to monitor.</p>
              </item>
              <tag><c>{RegisteredName, Node}</c></tag>
              <item>
		<p>A tuple consisting of a registered name of a process and
		a node name. The process residing on the node <c>Node</c>
		with the registered name <c>{RegisteredName, Node}</c> will
		be monitored.</p>
              </item>
              <tag><c>RegisteredName</c></tag>
              <item>
		<p>The process locally registered as <c>RegisteredName</c>
		will become monitored.</p>
              </item>
            </taglist>
            <note><p>When a process is monitored by registered name, the
	    process that has the registered name at the time when the
            monitor request reach its destination will be monitored.
            The monitor will not be effected, if the registered name is
            unregistered, or unregistered and later registered on another
	    process.</p></note>
	    <p>The monitor is triggered either when the monitored process
	    terminates, is non existing, or if the connection to it is
	    lost. In the case the connection to it is lost, we do not know
	    if it still exist or not. After this type of monitor has been
	    triggered, the monitor is automatically removed.</p>
            <p>When the monitor is triggered a <c>'DOWN'</c> message will
	    be sent to the monitoring process. A <c>'DOWN'</c> message has
	    the following pattern:</p>
            <code type="none">{'DOWN', MonitorRef, Type, Object, Info}</code>
            <p>where <c>MonitorRef</c> and <c>Type</c> are the same as
            described above, and:</p>
            <taglist>
              <tag><c>Object</c></tag>
              <item>
		<p>equals:</p>
		<taglist>
		  <tag><c><anno>Item</anno></c></tag>
		  <item>If <c><anno>Item</anno></c> was specified by a
		  pid.</item>
		  <tag><c>{RegisteredName, Node}</c></tag>
		  <item>If <c><anno>Item</anno></c> was specified as
		  <c>RegisteredName</c>, or <c>{RegisteredName, Node}</c>
		  where <c>Node</c> corresponds to the node that the
		  monitored process resides on.</item>
		</taglist>
              </item>
              <tag><c>Info</c></tag>
              <item>
		<p>Either the exit reason of the process, <c>noproc</c>
		(non-existing process), or <c>noconnection</c> (no
		connection to the node where the monitored process
		resides).</p></item>
	    </taglist>
	    <p>The monitoring is turned off either when the <c>'DOWN'</c>
	    message is sent, or when
	    <seealso marker="#demonitor/1">demonitor/1</seealso>
	    is called.</p>
	    <p>If an attempt is made to monitor a process on an older node
	    (where remote process monitoring is not implemented or one
	    where remote process monitoring by registered name is not
	    implemented), the call fails with <c>badarg</c>.</p>
	    <note>
	      <p>The format of the <c>'DOWN'</c> message changed in the 5.2
	      version of the emulator (OTP release R9B) for monitor
	      <em>by registered name</em>. The <c>Object</c> element of
	      the <c>'DOWN'</c> message could in earlier versions
	      sometimes be the pid of the monitored process and sometimes
	      be the registered name. Now the <c>Object</c> element is
	      always a tuple consisting of the registered name and
	      the node name. Processes on new nodes (emulator version 5.2
	      or greater) will always get <c>'DOWN'</c> messages on
	      the new format even if they are monitoring processes on old
	      nodes. Processes on old nodes will always get <c>'DOWN'</c>
	      messages on the old format.</p>
	    </note>
	  </item>
	  <tag><marker id="monitor_time_offset"/><c>time_offset</c></tag>
	  <item>
	    <p>Monitor changes in
	    <seealso marker="#time_offset/0">time offset</seealso>
	    between
	    <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang
	    monotonic time</seealso> and
	    <seealso marker="time_correction#Erlang_System_Time">Erlang
	    system time</seealso>. There is only one valid
	    <c><anno>Item</anno></c> in combination with the
	    <c>time_offset <anno>Type</anno></c>, namely the atom
	    <c>clock_service</c>. Note that the atom <c>clock_service</c> is
	    <em>not</em> the registered name of a process. In this specific
	    case it serves as an identifier of the runtime system internal
	    clock service at current runtime system instance.</p>

	    <p>The monitor is triggered when the time offset is changed.
	    This either if the time offset value is changed, or if the
	    offset is changed from preliminary to final during
	    <seealso marker="#system_flag_time_offset">finalization
	    of the time offset</seealso> when the
	    <seealso marker="time_correction#Single_Time_Warp_Mode">single
	    time warp mode</seealso> is used. When a change from preliminary
	    to final time offset is made, the monitor will be triggered once
	    regardless of whether the time offset value was changed due to
	    the finalization or not.</p>

	    <p>If the runtime system is in
	    <seealso marker="time_correction#Multi_Time_Warp_Mode">multi
	    time warp mode</seealso>, the time offset will be changed when
	    the runtime system detects that the
	    <seealso marker="time_correction#OS_System_Time">OS system
	    time</seealso> has changed. The runtime system will, however,
	    not detect this immediately when it happens. A task checking
	    the time offset is scheduled to execute at least once a minute,
	    so under normal operation this should be detected within a
	    minute, but during heavy load it might take longer time.</p>

	    <p>The monitor will <em>not</em> be automatically removed
	    after it has been triggered. That is, repeated changes of
	    the time offset will trigger the monitor repeatedly.</p>

            <p>When the monitor is triggered a <c>'CHANGE'</c> message will
	    be sent to the monitoring process. A <c>'CHANGE'</c> message has
	    the following pattern:</p>
            <code type="none">{'CHANGE', MonitorRef, Type, Item, NewTimeOffset}</code>
            <p>where <c>MonitorRef</c>, <c><anno>Type</anno></c>, and 
	    <c><anno>Item</anno></c> are the same as described above, and
	    <c>NewTimeOffset</c> is the new time offset.</p>

	    <p>When the <c>'CHANGE'</c> message has been received you are
	    guaranteed not to retrieve the old time offset when calling
	    <seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso>.
	    Note that you may observe the change of the time offset
	    when calling <c>erlang:time_offset()</c> before you
	    get the <c>'CHANGE'</c> message.</p>

	  </item>
	</taglist>
	<p>Making several calls to <c>monitor/2</c> for the same
	<c><anno>Item</anno></c> and/or <c><anno>Type</anno></c> is not
	an error; it results in many, completely independent,
	monitorings.</p>
	<p>The monitor functionality is expected to be extended. That is,
	other <c><anno>Type</anno></c>s and <c><anno>Item</anno></c>s
	are expected to be supported in	the future.</p>
        <note>
          <p>If/when <c>monitor/2</c> is extended, other
            possible values for <c>Tag</c>, <c>Object</c>, and
	    <c>Info</c> in the monitor message will be introduced.</p>
        </note>
      </desc>
    </func>
    <func>
      <name name="monitor_node" arity="2"/>
      <fsummary>Monitor the status of a node</fsummary>
      <desc>
        <p>Monitors the status of the node <c><anno>Node</anno></c>. If <c><anno>Flag</anno></c>
          is <c>true</c>, monitoring is turned on; if <c><anno>Flag</anno></c> is
          <c>false</c>, monitoring is turned off.</p>
        <p>Making several calls to <c>monitor_node(Node, true)</c> for
          the same <c><anno>Node</anno></c> is not an error; it results in as many,
          completely independent, monitorings.</p>
        <p>If <c><anno>Node</anno></c> fails or does not exist, the message
          <c>{nodedown, Node}</c> is delivered to the process. If a
          process has made two calls to <c>monitor_node(Node, true)</c>
          and <c><anno>Node</anno></c> terminates, two <c>nodedown</c> messages are
          delivered to the process. If there is no connection to
          <c><anno>Node</anno></c>, there will be an attempt to create one. If this
          fails, a <c>nodedown</c> message is delivered.</p>
        <p>Nodes connected through hidden connections can be monitored
          as any other node.</p>
        <p>Failure: <c>badarg</c> if the local node is not alive.</p>
      </desc>
    </func>
    <func>
      <name name="monitor_node" arity="3"/>
      <fsummary>Monitor the status of a node</fsummary>
      <desc>
        <p>Behaves as <c>monitor_node/2</c> except that it allows an
          extra option to be given, namely <c>allow_passive_connect</c>.
          The option allows the BIF to wait the normal net connection
          timeout for the <em>monitored node</em> to connect itself,
          even if it cannot be actively connected from this node
          (i.e. it is blocked). The state where this might be useful can
          only be achieved by using the kernel option
          <c>dist_auto_connect once</c>. If that kernel option is not
          used, the <c>allow_passive_connect</c> option has no
          effect.</p>
        <note>
          <p>The <c>allow_passive_connect</c> option is used
            internally and is seldom needed in applications where the
            network topology and the kernel options in effect is known in
            advance.</p>
        </note>
        <p>Failure: <c>badarg</c> if the local node is not alive or the
          option list is malformed.</p>
      </desc>
    </func>
    <func>
      <name name="monotonic_time" arity="0"/>
      <fsummary>Current Erlang monotonic time</fsummary>
      <desc>
	<p>Returns the current
	<seealso marker="time_correction#Erlang_Monotonic_Time">Erlang
	monotonic time</seealso> in <c>native</c>
	<seealso marker="#type_time_unit">time unit</seealso>. This
	is a monotonically increasing time since some unspecified point in
	time.</p>

	<note><p>This is a
	<seealso marker="time_correction#Monotonically_Increasing">monotonically increasing</seealso> time, but <em>not</em> a
	<seealso marker="time_correction#Strictly_Monotonically_Increasing">strictly monotonically increasing</seealso>
	time. That is, consecutive calls to
	<c>erlang:monotonic_time/0</c> may produce the same result.</p>

	<p>Different runtime system instances will use different
	unspecified points in time as base for their Erlang monotonic clocks.
	That is, it is <em>pointless</em> comparing monotonic times from
	different runtime system instances. Different runtime system instances
	may also place this unspecified point in time different relative
	runtime system start. It may be placed in the future (time at start
	will be a negative value), the past (time at start will be a
	positive value), or the runtime system start (time at start will
	be zero). The monotonic time as of runtime system start can be
	retrieved by calling
	<seealso marker="#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso>.</p></note>
      </desc>
    </func>
    <func>
      <name name="monotonic_time" arity="1"/>
      <fsummary>Current Erlang monotonic time</fsummary>
      <desc>
	<p>Returns the current
	<seealso marker="time_correction#Erlang_Monotonic_Time">Erlang
	monotonic time</seealso> converted
	into the <c><anno>Unit</anno></c> passed as argument.</p>

	<p>Same as calling
	<seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#monotonic_time/0"><c>erlang:monotonic_time()</c></seealso><c>,
	native, <anno>Unit</anno>)</c>
	however optimized for commonly used <c><anno>Unit</anno></c>s.</p>
      </desc>
    </func>
    <func>
      <name name="nif_error" arity="1"/>
      <fsummary>Stop execution with a given reason</fsummary>
      <desc>
        <p>Works exactly like
	 <seealso marker="#error/1">erlang:error/1</seealso>,
	 but Dialyzer thinks that this BIF will return an arbitrary term.
	 When used in a stub function for a NIF to generate an
	 exception when the NIF library is not loaded, Dialyzer
	 will not generate false warnings.</p>
      </desc>
    </func>
    <func>
      <name name="nif_error" arity="2"/>
      <fsummary>Stop execution with a given reason</fsummary>
      <desc>
        <p>Works exactly like
	 <seealso marker="#error/2">erlang:error/2</seealso>,
	 but Dialyzer thinks that this BIF will return an arbitrary term.
	 When used in a stub function for a NIF to generate an
	 exception when the NIF library is not loaded, Dialyzer
	 will not generate false warnings.</p>
      </desc>
    </func>
    <func>
      <name name="node" arity="0"/>
      <fsummary>Name of the local node</fsummary>
      <desc>
        <p>Returns the name of the local node. If the node is not alive,
          <c>nonode@nohost</c> is returned instead.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="node" arity="1"/>
      <fsummary>At which node is a pid, port or reference located</fsummary>
      <desc>
        <p>Returns the node where <c><anno>Arg</anno></c> is located. <c><anno>Arg</anno></c> can
          be a pid, a reference, or a port. If the local node is not
          alive, <c>nonode@nohost</c> is returned.</p>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="nodes" arity="0"/>
      <fsummary>All visible nodes in the system</fsummary>
      <desc>
        <p>Returns a list of all visible nodes in the system, excluding
          the local node. Same as <c>nodes(visible)</c>.</p>
      </desc>
    </func>
    <func>
      <name name="nodes" arity="1"/>
      <fsummary>All nodes of a certain type in the system</fsummary>
      <desc>
        <p>Returns a list of nodes according to argument given.
          The result returned when the argument is a list, is the list
          of nodes satisfying the disjunction(s) of the list elements.</p>
        <p><c><anno>NodeType</anno></c> can be any of the following:</p>
        <taglist>
          <tag><c>visible</c></tag>
          <item>
            <p>Nodes connected to this node through normal connections.</p>
          </item>
          <tag><c>hidden</c></tag>
          <item>
            <p>Nodes connected to this node through hidden connections.</p>
          </item>
          <tag><c>connected</c></tag>
          <item>
            <p>All nodes connected to this node.</p>
          </item>
          <tag><c>this</c></tag>
          <item>
            <p>This node.</p>
          </item>
          <tag><c>known</c></tag>
          <item>
            <p>Nodes which are known to this node, i.e., connected,
              previously connected, etc.</p>
          </item>
        </taglist>
        <p>Some equalities: <c>[node()] = nodes(this)</c>,
          <c>nodes(connected) = nodes([visible, hidden])</c>, and
          <c>nodes() = nodes(visible)</c>.</p>
        <p>If the local node is not alive,
          <c>nodes(this) == nodes(known) == [nonode@nohost]</c>, for
          any other <c><anno>Arg</anno></c> the empty list [] is returned.</p>
      </desc>
    </func>
    <func>
      <name name="now" arity="0"/>
      <type name="timestamp"/>
      <fsummary>Elapsed time since 00:00 GMT</fsummary>
      <desc>
	<warning><p><em>This function is deprecated! Do not use it!</em>
	See the users guide chapter
	<seealso marker="time_correction">Time and Time Correction</seealso>
	for more information. Specifically the 
	<seealso marker="time_correction#Dos_and_Donts">Dos and Dont's</seealso>
	section for information on what to use instead of <c>erlang:now/0</c>.
	</p></warning>
        <p>Returns the tuple <c>{MegaSecs, Secs, MicroSecs}</c> which is
          the elapsed time since 00:00 GMT, January 1, 1970 (zero hour)
          on the assumption that the underlying OS supports this.
          Otherwise, some other point in time is chosen. It is also
          guaranteed that subsequent calls to this BIF returns
          continuously increasing values. Hence, the return value from
          <c>now()</c> can be used to generate unique time-stamps,
          and if it is called in a tight loop on a fast machine
          the time of the node can become skewed.</p>
        <p>It can only be used to check the local time of day if
          the time-zone info of the underlying operating system is
          properly configured.</p>
      </desc>
    </func>
    <func>
      <name name="open_port" arity="2"/>
      <fsummary>Open a port</fsummary>
      <desc>
        <p>Returns a port identifier as the result of opening a
          new Erlang port. A port can be seen as an external Erlang
          process.
	</p>
	<p>The name of the executable as well as the arguments
	given in <c>cd</c>, <c>env</c>, <c>args</c> and <c>arg0</c> is subject to
	Unicode file name translation if the system is running
	in Unicode file name mode. To avoid
	translation or force i.e. UTF-8, supply the executable
	and/or arguments as a binary in the correct
	encoding. See the <seealso
	marker="kernel:file">file</seealso> module, the
	<seealso marker="kernel:file#native_name_encoding/0">
	  file:native_name_encoding/0</seealso> function and the
	  <seealso marker="stdlib:unicode_usage">stdlib users guide
	</seealso> for details.</p>

	<note><p>The characters in the name (if given as a list)
	can only be &gt; 255 if the Erlang VM is started in
	Unicode file name translation mode, otherwise the name
	of the executable is limited to the ISO-latin-1
	character set.</p></note>

	<p><c><anno>PortName</anno></c> is one of the following:</p>
        <taglist>
          <tag><c>{spawn, <anno>Command</anno>}</c></tag>
          <item>
            <p>Starts an external program. <c><anno>Command</anno></c> is the name
              of the external program which will be run. <c><anno>Command</anno></c>
              runs outside the Erlang work space unless an Erlang
              driver with the name <c><anno>Command</anno></c> is found. If found,
              that driver will be started. A driver runs in the Erlang
              workspace, which means that it is linked with the Erlang
              runtime system.</p>
            <p>When starting external programs on Solaris, the system
              call <c>vfork</c> is used in preference to <c>fork</c>
              for performance reasons, although it has a history of
              being less robust. If there are problems with using
              <c>vfork</c>, setting the environment variable
              <c>ERL_NO_VFORK</c> to any value will cause <c>fork</c>
              to be used instead.</p>

	      <p>For external programs, the <c>PATH</c> is searched
	      (or an equivalent method is used to find programs,
	      depending on operating system). This is done by invoking
	      the shell on certain platforms. The first space
	      separated token of the command will be considered as the
	      name of the executable (or driver). This (among other
	      things) makes this option unsuitable for running
	      programs having spaces in file or directory names. Use
	      {spawn_executable, <anno>Command</anno>} instead if spaces in executable
	      file names is desired.</p>
          </item>
          <tag><c>{spawn_driver, <anno>Command</anno>}</c></tag>
          <item>
	      <p>Works like <c>{spawn, <anno>Command</anno>}</c>, but demands the
	      first (space separated) token of the command to be the name of a
	      loaded driver. If no driver with that name is loaded, a
	      <c>badarg</c> error is raised.</p>
          </item>
          <tag><c>{spawn_executable, <anno>FileName</anno>}</c></tag>
          <item>

	      <p>Works like <c>{spawn, <anno>FileName</anno>}</c>, but only runs
	      external executables. The <c><anno>FileName</anno></c> in its whole
	      is used as the name of the executable, including any
	      spaces. If arguments are to be passed, the
	      <c>args</c> and <c>arg0</c> <c><anno>PortSettings</anno></c> can be used.</p>

	      <p>The shell is not usually invoked to start the
	      program, it's executed directly. Neither is the
	      <c>PATH</c> (or equivalent) searched. To find a program
	      in the PATH to execute, use <seealso
	      marker="kernel:os#find_executable/1">os:find_executable/1</seealso>.</p>
	      <p>Only if a shell script or <c>.bat</c> file is
	      executed, the appropriate command interpreter will
	      implicitly be invoked, but there will still be no
	      command argument expansion or implicit PATH search.</p>
  
	      <p>If the <c><anno>FileName</anno></c> cannot be run, an error
	      exception, with the posix error code as the reason, is
	      raised. The error reason may differ between operating
	      systems. Typically the error <c>enoent</c> is raised
	      when one tries to run a program that is not found and
	      <c>eacces</c> is raised when the given file is not
	      executable.</p>
          </item>
          <tag><c>{fd, <anno>In</anno>, <anno>Out</anno>}</c></tag>
          <item>
            <p>Allows an Erlang process to access any currently opened
              file descriptors used by Erlang. The file descriptor
              <c><anno>In</anno></c> can be used for standard input, and the file
              descriptor <c><anno>Out</anno></c> for standard output. It is only
              used for various servers in the Erlang operating system
              (<c>shell</c> and <c>user</c>). Hence, its use is very
              limited.</p>
          </item>
        </taglist>
        <p><c><anno>PortSettings</anno></c> is a list of settings for the port.
          Valid settings are:</p>
        <taglist>
          <tag><c>{packet, <anno>N</anno>}</c></tag>
          <item>
            <p>Messages are preceded by their length, sent in <c><anno>N</anno></c>
              bytes, with the most significant byte first. Valid values
              for <c>N</c> are 1, 2, or 4.</p>
          </item>
          <tag><c>stream</c></tag>
          <item>
            <p>Output messages are sent without packet lengths. A
              user-defined protocol must be used between the Erlang
              process and the external object.</p>
          </item>
          <tag><c>{line, <anno>L</anno>}</c></tag>
          <item>
            <p>Messages are delivered on a per line basis. Each line
              (delimited by the OS-dependent newline sequence) is
              delivered in one single message. The message data format
              is <c>{Flag, Line}</c>, where <c>Flag</c> is either
              <c>eol</c> or <c>noeol</c> and <c>Line</c> is the actual
              data delivered (without the newline sequence).</p>
            <p><c><anno>L</anno></c> specifies the maximum line length in bytes.
              Lines longer than this will be delivered in more than one
              message, with the <c>Flag</c> set to <c>noeol</c> for all
              but the last message. If end of file is encountered
              anywhere else than immediately following a newline
              sequence, the last line will also be delivered with
              the <c>Flag</c> set to <c>noeol</c>. In all other cases,
              lines are delivered with <c>Flag</c> set to <c>eol</c>.</p>
            <p>The <c>{packet, <anno>N</anno>}</c> and <c>{line, <anno>L</anno>}</c> settings are
              mutually exclusive.</p>
          </item>
          <tag><c>{cd, <anno>Dir</anno>}</c></tag>
          <item>
            <p>This is only valid for <c>{spawn, <anno>Command</anno>}</c> and
	    <c>{spawn_executable, <anno>FileName</anno>}</c>.
              The external program starts using <c><anno>Dir</anno></c> as its
              working directory. <c><anno>Dir</anno></c> must be a string.
		  </p>
          </item>
          <tag><c>{env, <anno>Env</anno>}</c></tag>
          <item>
            <p>This is only valid for <c>{spawn, <anno>Command</anno>}</c> and
	    <c>{spawn_executable, <anno>FileName</anno>}</c>.
              The environment of the started process is extended using
              the environment specifications in <c><anno>Env</anno></c>.</p>
            <p><c><anno>Env</anno></c> should be a list of tuples <c>{<anno>Name</anno>, <anno>Val</anno>}</c>,
              where <c><anno>Name</anno></c> is the name of an environment variable,
              and <c><anno>Val</anno></c> is the value it is to have in the spawned
              port process. Both <c><anno>Name</anno></c> and <c><anno>Val</anno></c> must be
              strings. The one exception is <c><anno>Val</anno></c> being the atom
              <c>false</c> (in analogy with <c>os:getenv/1</c>), which
              removes the environment variable.
	    </p>
          </item>
	  <tag><c>{args, [ string() | binary() ]}</c></tag>
          <item>

	    <p>This option is only valid for <c>{spawn_executable, <anno>FileName</anno>}</c>
	    and specifies arguments to the executable. Each argument
	    is given as a separate string and (on Unix) eventually
	    ends up as one element each in the argument vector. On
	    other platforms, similar behavior is mimicked.</p>

	    <p>The arguments are not expanded by the shell prior to
	      being supplied to the executable, most notably this
	      means that file wildcard expansion will not happen. Use
	      <seealso
	      marker="stdlib:filelib#wildcard/1">filelib:wildcard/1</seealso>
	      to expand wildcards for the arguments. Note that even if
	      the program is a Unix shell script, meaning that the
	      shell will ultimately be invoked, wildcard expansion
	      will not happen and the script will be provided with the
	      untouched arguments. On Windows&reg;, wildcard expansion
	      is always up to the program itself, why this isn't an
	      issue.</p>

	    <p>Note also that the actual executable name (a.k.a. <c>argv[0]</c>)
	    should not be given in this list. The proper executable name will
	    automatically be used as argv[0] where applicable.</p>

	    <p>If one, for any reason, wants to explicitly set the
	    program name in the argument vector, the <c>arg0</c>
	    option can be used.</p>

          </item>
	  <tag><c>{arg0, string() | binary()}</c></tag>
          <item>

	    <p>This option is only valid for <c>{spawn_executable, <anno>FileName</anno>}</c>
	    and explicitly specifies the program name argument when
	    running an executable. This might in some circumstances,
	    on some operating systems, be desirable. How the program
	    responds to this is highly system dependent and no specific 
	    effect is guaranteed.</p>

	  </item> 

          <tag><c>exit_status</c></tag>
          <item>
            <p>This is only valid for <c>{spawn, <anno>Command</anno>}</c> where
              <c><anno>Command</anno></c> refers to an external program, and for
	      <c>{spawn_executable, <anno>FileName</anno>}</c>.</p>
            <p>When the external process connected to the port exits, a
              message of the form <c>{Port,{exit_status,Status}}</c> is
              sent to the connected process, where <c>Status</c> is the
              exit status of the external process. If the program
              aborts, on Unix the same convention is used as the shells
              do (i.e., 128+signal).</p>
            <p>If the <c>eof</c> option has been given as well,
              the <c>eof</c> message and the <c>exit_status</c> message
              appear in an unspecified order.</p>
            <p>If the port program closes its stdout without exiting,
              the <c>exit_status</c> option will not work.</p>
          </item>
          <tag><c>use_stdio</c></tag>
          <item>
            <p>This is only valid for <c>{spawn, <anno>Command</anno>}</c> and
	    <c>{spawn_executable, <anno>FileName</anno>}</c>. It
              allows the standard input and output (file descriptors 0
              and 1) of the spawned (UNIX) process for communication
              with Erlang.</p>
          </item>
          <tag><c>nouse_stdio</c></tag>
          <item>
            <p>The opposite of <c>use_stdio</c>. Uses file descriptors
              3 and 4 for communication with Erlang.</p>
          </item>
          <tag><c>stderr_to_stdout</c></tag>
          <item>
            <p>Affects ports to external programs. The executed program
              gets its standard error file redirected to its standard
              output file. <c>stderr_to_stdout</c> and
              <c>nouse_stdio</c> are mutually exclusive.</p>
          </item>
          <tag><c>overlapped_io</c></tag>
          <item>
            <p>Affects ports to external programs on Windows&reg; only.
	    The standard input and standard output handles of the port program
	    will, if this option is supplied, be opened with the flag
	    FILE_FLAG_OVERLAPPED, so that the port program can (and has to) do
	    overlapped I/O on its standard handles. This is not normally
	    the case for simple port programs, but an option of value for the
	    experienced Windows programmer. <em>On all other platforms, this 
	    option is silently discarded</em>.</p> 
          </item>
          <tag><c>in</c></tag>
          <item>
            <p>The port can only be used for input.</p>
          </item>
          <tag><c>out</c></tag>
          <item>
            <p>The port can only be used for output.</p>
          </item>
          <tag><c>binary</c></tag>
          <item>
            <p>All IO from the port are binary data objects as opposed
              to lists of bytes.</p>
          </item>
          <tag><c>eof</c></tag>
          <item>
            <p>The port will not be closed at the end of the file and
              produce an exit signal. Instead, it will remain open and
              a <c>{Port, eof}</c> message will be sent to the process
              holding the port.</p>
          </item>
          <tag><c>hide</c></tag>
          <item>
            <p>When running on Windows, suppress creation of a new
	      console window when spawning the port program.
	      (This option has no effect on other platforms.)</p>
          </item>
          <tag><marker id="open_port_parallelism"><c>{parallelism, Boolean}</c></marker></tag>
          <item>
            <p>Set scheduler hint for port parallelism. If set to <c>true</c>,
	    the VM will schedule port tasks when doing so will improve
	    parallelism in the system. If set to <c>false</c>, the VM will
	    try to perform port tasks immediately, improving latency at the
            expense of parallelism. The default can be set on system startup
            by passing the
	    <seealso marker="erl#+spp">+spp</seealso> command line argument
	    to <seealso marker="erl">erl(1)</seealso>.
	    </p>
          </item>
        </taglist>
        <p>The default is <c>stream</c> for all types of port and
          <c>use_stdio</c> for spawned ports.</p>
        <p>Failure: If the port cannot be opened, the exit reason is
	  <c>badarg</c>, <c>system_limit</c>, or the Posix error code which
	  most closely describes the error, or <c>einval</c> if no Posix code
	  is appropriate:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
            <p>Bad input arguments to <c>open_port</c>.</p>
          </item>
          <tag><c>system_limit</c></tag>
          <item>
            <p>All available ports in the Erlang emulator are in use.</p>
          </item>
          <tag><c>enomem</c></tag>
          <item>
            <p>There was not enough memory to create the port.</p>
          </item>
          <tag><c>eagain</c></tag>
          <item>
            <p>There are no more available operating system processes.</p>
          </item>
          <tag><c>enametoolong</c></tag>
          <item>
            <p>The external command given was too long.</p>
          </item>
          <tag><c>emfile</c></tag>
          <item>
            <p>There are no more available file descriptors (for the operating system process
	    that the Erlang emulator runs in).</p>
          </item>
          <tag><c>enfile</c></tag>
          <item>
            <p>The file table is full (for the entire operating system).</p>
          </item>
          <tag><c>eacces</c></tag>
          <item>
            <p>The <c>Command</c> given in <c>{spawn_executable, Command}</c> does not point out an executable file.</p>
          </item>
          <tag><c>enoent</c></tag>
          <item>
            <p>The <c><anno>FileName</anno></c> given in <c>{spawn_executable, <anno>FileName</anno>}</c> does not point out an existing file.</p>
          </item>
        </taglist>
        <p>During use of a port opened using <c>{spawn, Name}</c>,
          <c>{spawn_driver, Name}</c> or <c>{spawn_executable, Name}</c>,
          errors arising when sending messages to it are reported to
          the owning process using signals of the form
          <c>{'EXIT', Port, PosixCode}</c>. See <c>file(3)</c> for
          possible values of <c>PosixCode</c>.</p>
	  <p>The maximum number of ports that can be open at the same
          time can be configured by passing the 
	  <seealso marker="erl#max_ports"><c>+Q</c></seealso>
	  command line flag to
	  <seealso marker="erl"><c>erl(1)</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="phash" arity="2"/>
      <type_desc variable="Range">Range = 1..2^32, Hash = 1..Range</type_desc>
      <fsummary>Portable hash function</fsummary>
      <desc>
        <p>Portable hash function that will give the same hash for
          the same Erlang term regardless of machine architecture and
          ERTS version (the BIF was introduced in ERTS 4.9.1.1). Range
          can be between 1 and 2^32, the function returns a hash value
          for <c><anno>Term</anno></c> within the range <c>1..<anno>Range</anno></c>.</p>
        <p>This BIF could be used instead of the old deprecated
          <c>erlang:hash/2</c> BIF, as it calculates better hashes for
          all data-types, but consider using <c>phash2/1,2</c> instead.</p>
      </desc>
    </func>
    <func>
      <name name="phash2" arity="1"/>
      <name name="phash2" arity="2"/>
      <type_desc variable="Range">1..2^32</type_desc>
      <type_desc variable="Hash">0..Range-1</type_desc>
      <fsummary>Portable hash function</fsummary>
      <desc>
        <p>Portable hash function that will give the same hash for
          the same Erlang term regardless of machine architecture and
          ERTS version (the BIF was introduced in ERTS 5.2). Range can
          be between 1 and 2^32, the function returns a hash value for
          <c><anno>Term</anno></c> within the range <c>0..<anno>Range</anno>-1</c>. When called
          without the <c><anno>Range</anno></c> argument, a value in the range
          <c>0..2^27-1</c> is returned.</p>
        <p>This BIF should always be used for hashing terms. It
          distributes small integers better than <c>phash/2</c>, and
          it is faster for bignums and binaries.</p>
        <p>Note that the range <c>0..<anno>Range</anno>-1</c> is different from
          the range of <c>phash/2</c> (<c>1..<anno>Range</anno></c>).</p>
      </desc>
    </func>
    <func>
      <name name="pid_to_list" arity="1"/>
      <fsummary>Text representation of a pid</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Pid</anno></c>.</p>
        <warning>
          <p>This BIF is intended for debugging and for use in
            the Erlang operating system. It should not be used in
            application programs.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="port_close" arity="1"/>
      <fsummary>Close an open port</fsummary>
      <desc>
        <p>Closes an open port. Roughly the same as
          <c><anno>Port</anno> ! {self(), close}</c> except for the error behaviour
          (see below), being synchronous, and that the port does
	  <em>not</em> reply with <c>{Port, closed}</c>. Any process may
	  close a port with <c>port_close/1</c>, not only the port owner
	  (the connected process). If the calling process is linked to
	  port identified by <c><anno>Port</anno></c>, an exit signal due
	  to that link will be received by the process prior to the return
	  from <c>port_close/1</c>.</p>
        <p>For comparison: <c><anno>Port</anno> ! {self(), close}</c> fails with
          <c>badarg</c> if <c><anno>Port</anno></c> cannot be sent to (i.e.,
          <c><anno>Port</anno></c> refers neither to a port nor to a process). If
          <c><anno>Port</anno></c> is a closed port nothing happens. If <c><anno>Port</anno></c>
          is an open port and the calling process is the port owner,
          the port replies with <c>{Port, closed}</c> when all buffers
          have been flushed and the port really closes, but if
          the calling process is not the port owner the <em>port owner</em> fails with <c>badsig</c>.</p>

        <p>Note that any process can close a port using
          <c><anno>Port</anno> ! {PortOwner, close}</c> just as if it itself was
          the port owner, but the reply always goes to the port owner.</p>
	<p>As of OTP-R16 <c><anno>Port</anno> ! {PortOwner, close}</c> is truly
	   asynchronous. Note that this operation has always been
	   documented as an asynchronous operation, while the underlying
	   implementation has been synchronous. <c>port_close/1</c> is
	   however still fully synchronous. This due to its error
	   behavior.</p>
        <p>Failure:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Port</anno></c> is not an identifier of an open
	     port, or the registered name of an open port. If the calling
	     process was linked to the previously open port identified by
	     <c><anno>Port</anno></c>, an exit signal due to this link
	     was received by the process prior to this exception.
	  </item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="port_command" arity="2"/>
      <fsummary>Send data to a port</fsummary>
      <desc>
        <p>Sends data to a port. Same as
          <c><anno>Port</anno> ! {PortOwner, {command, Data}}</c> except for the error
          behaviour and being synchronous (see below). Any process may
	  send data to a port with <c>port_command/2</c>, not only the
	  port owner (the connected process).</p>
        <p>For comparison: <c><anno>Port</anno> ! {PortOwner, {command, Data}}</c>
          fails with <c>badarg</c> if <c><anno>Port</anno></c> cannot be sent to
          (i.e., <c><anno>Port</anno></c> refers neither to a port nor to a process).
          If <c><anno>Port</anno></c> is a closed port the data message disappears
          without a sound. If <c><anno>Port</anno></c> is open and the calling
          process is not the port owner, the <em>port owner</em> fails
          with <c>badsig</c>. The port owner fails with <c>badsig</c>
          also if <c><anno>Data</anno></c> is not a valid IO list.</p>
        <p>Note that any process can send to a port using
          <c><anno>Port</anno> ! {PortOwner, {command, <anno>Data</anno>}}</c> just as if it
          itself was the port owner.</p>
	<p>If the port is busy, the calling process will be suspended
	   until the port is not busy anymore.</p>
	<p>As of OTP-R16 <c><anno>Port</anno> ! {PortOwner, {command, Data}}</c> is
	   truly asynchronous. Note that this operation has always been
	   documented as an asynchronous operation, while the underlying
	   implementation has been synchronous. <c>port_command/2</c> is
	   however still fully synchronous. This due to its error
	   behavior.</p>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Port</anno></c> is not an identifier of an open
	     port, or the registered name of an open port. If the calling
	     process was linked to the previously open port identified by
	     <c><anno>Port</anno></c>, an exit signal due to this link
	     was received by the process prior to this exception.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Data</anno></c> is not a valid io list.
	  </item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="port_command" arity="3"/>
      <fsummary>Send data to a port</fsummary>
      <desc>
        <p>Sends data to a port. <c>port_command(Port, Data, [])</c>
	  equals <c>port_command(Port, Data)</c>.</p>
	<p>If the port command is aborted <c>false</c> is returned;
	   otherwise, <c>true</c> is returned.</p>
	<p>If the port is busy, the calling process will be suspended
	   until the port is not busy anymore.</p>
        <p>Currently the following <c><anno>Option</anno></c>s are valid:</p>
        <taglist>
          <tag><c>force</c></tag>
          <item>The calling process will not be suspended if the port is
	        busy; instead, the port command is forced through. The
		call will fail with a <c>notsup</c> exception if the
		driver of the port does not support this. For more
		information see the
		<seealso marker="driver_entry#driver_flags"><![CDATA[ERL_DRV_FLAG_SOFT_BUSY]]></seealso>
		driver flag.
          </item>
          <tag><c>nosuspend</c></tag>
          <item>The calling process will not be suspended if the port is
	        busy; instead, the port command is aborted and
		<c>false</c> is returned. 
          </item>
        </taglist>
        <note>
          <p>More options may be added in the future.</p>
        </note>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Port</anno></c> is not an identifier of an open
	     port, or the registered name of an open port. If the calling
	     process was linked to the previously open port identified by
	     <c><anno>Port</anno></c>, an exit signal due to this link
	     was received by the process prior to this exception.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Data</anno></c> is not a valid io list.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	    If <c><anno>OptionList</anno></c> is not a valid option list.
	  </item>
          <tag><c>notsup</c></tag>
          <item>
	    If the <c>force</c> option has been passed, but the
	    driver of the port does not allow forcing through
	    a busy port.
	  </item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="port_connect" arity="2"/>
      <fsummary>Set the owner of a port</fsummary>
      <desc>
        <p>Sets the port owner (the connected port) to <c><anno>Pid</anno></c>.
          Roughly the same as <c><anno>Port</anno> ! {Owner, {connect, <anno>Pid</anno>}}</c>
          except for the following:</p>
        <list type="bulleted">
          <item>
            <p>The error behavior differs, see below.</p>
          </item>
          <item>
            <p>The port does <em>not</em> reply with
              <c>{Port,connected}</c>.</p>
          </item>
          <item>
            <p><c>port_connect/1</c> is synchronous, see below.</p>
          </item>
          <item>
            <p>The new port owner gets linked to the port.</p>
          </item>
        </list>
        <p>The old port owner stays linked to the port and have to call
          <c>unlink(Port)</c> if this is not desired. Any process may
          set the port owner to be any process with
          <c>port_connect/2</c>.</p>
        <p>For comparison: <c><anno>Port</anno> ! {self(), {connect, <anno>Pid</anno>}}</c> fails
          with <c>badarg</c> if <c><anno>Port</anno></c> cannot be sent to (i.e.,
          <c><anno>Port</anno></c> refers neither to a port nor to a process). If
          <c><anno>Port</anno></c> is a closed port nothing happens. If <c><anno>Port</anno></c>
          is an open port and the calling process is the port owner,
          the port replies with <c>{Port, connected}</c> to the old
          port owner. Note that the old port owner is still linked to
          the port, and that the new is not. If <c><anno>Port</anno></c> is an open
          port and the calling process is not the port owner,
          the <em>port owner</em> fails with <c>badsig</c>. The port
          owner fails with <c>badsig</c> also if <c><anno>Pid</anno></c> is not an
          existing local pid.</p>
        <p>Note that any process can set the port owner using
          <c><anno>Port</anno> ! {PortOwner, {connect, <anno>Pid</anno>}}</c> just as if it
          itself was the port owner, but the reply always goes to
          the port owner.</p>
	<p>As of OTP-R16 <c><anno>Port</anno> ! {PortOwner, {connect, <anno>Pid</anno>}}</c> is
	   truly asynchronous. Note that this operation has always been
	   documented as an asynchronous operation, while the underlying
	   implementation has been synchronous. <c>port_connect/2</c> is
	   however still fully synchronous. This due to its error
	   behavior.</p>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Port</anno></c> is not an identifier of an open
	     port, or the registered name of an open port. If the calling
	     process was linked to the previously open port identified by
	     <c><anno>Port</anno></c>, an exit signal due to this link
	     was received by the process prior to this exception.
	  </item>
          <tag><c>badarg</c></tag>
	  <item>If process identified by <c>Pid</c> is not an existing
	  local process.</item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="port_control" arity="3"/>
      <fsummary>Perform a synchronous control operation on a port</fsummary>
      <desc>
        <p>Performs a synchronous control operation on a port.
          The meaning of <c><anno>Operation</anno></c> and <c><anno>Data</anno></c> depends on
          the port, i.e., on the port driver. Not all port drivers
          support this control feature.</p>
        <p>Returns: a list of integers in the range 0 through 255, or a
          binary, depending on the port driver. The meaning of
          the returned data also depends on the port driver.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not an open port or
          the registered name of an open port, if <c><anno>Operation</anno></c>
          cannot fit in a 32-bit integer, if the port driver does not
          support synchronous control operations, or if the port driver
          so decides for any reason (probably something wrong with
          <c><anno>Operation</anno></c> or <c><anno>Data</anno></c>).</p>
      </desc>
    </func>
    <func>
      <name name="port_call" arity="3"/>
      <fsummary>Synchronous call to a port with term data</fsummary>
      <desc>
        <p>Performs a synchronous call to a port. The meaning of
          <c><anno>Operation</anno></c> and <c><anno>Data</anno></c> depends on the port, i.e.,
          on the port driver. Not all port drivers support this feature.</p>
        <p><c><anno>Port</anno></c> is a port identifier, referring to a driver.</p>
        <p><c><anno>Operation</anno></c> is an integer, which is passed on to
          the driver.</p>
        <p><c><anno>Data</anno></c> is any Erlang term. This data is converted to
          binary term format and sent to the port.</p>
        <p>Returns: a term from the driver. The meaning of the returned
          data also depends on the port driver.</p>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	     If <c><anno>Port</anno></c> is not an identifier of an open
	     port, or the registered name of an open port. If the calling
	     process was linked to the previously open port identified by
	     <c><anno>Port</anno></c>, an exit signal due to this link
	     was received by the process prior to this exception.
	  </item>
          <tag><c>badarg</c></tag>
	  <item>
	     If <c><anno>Operation</anno></c> does not fit in a
	     32-bit integer.
	  </item>
          <tag><c>badarg</c></tag>
	  <item>
	     If the port driver does not support synchronous control
	     operations.
	  </item>
          <tag><c>badarg</c></tag>
	  <item>
	     If the port driver so decides for any reason (probably
	     something wrong with <c><anno>Operation</anno></c>, or
	     <c><anno>Data</anno></c>).
	  </item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="1"/>
      <fsummary>Information about a port</fsummary>
      <desc>
        <p>Returns a list containing tuples with information about
          the <c><anno>Port</anno></c>, or <c>undefined</c> if the port is not open.
          The order of the tuples is not defined, nor are all the
          tuples mandatory.
	  If <c>undefined</c> is returned and the calling process
	  was linked to a previously open port identified by
	  <c><anno>Port</anno></c>, an exit signal due to this link
	  was received by the process prior to the return from
	  <c>port_info/1</c>.</p>
	<p>Currently the result will containt information about the
	following <c>Item</c>s: <c>registered_name</c> (if the port has
	a registered name), <c>id</c>, <c>connected</c>, <c>links</c>,
	<c>name</c>, <c>input</c>, and <c>output</c>. For more information
	about the different <c>Item</c>s, see
	<seealso marker="#port_info/2">port_info/2</seealso>.</p>
        <p>Failure: <c>badarg</c> if <c>Port</c> is not a local port
	identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="1"/>
      <fsummary>Information about the connected process of a port</fsummary>
      <desc>
	<p><c><anno>Pid</anno></c> is the process identifier of the process
	connected to the port.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="2"/>
      <fsummary>Information about the internal index of a port</fsummary>
      <desc>
	<p><c><anno>Index</anno></c> is the internal index of the port. This
	index may be used to separate ports.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="3"/>
      <fsummary>Information about the input of a port</fsummary>
      <desc>
	<p><c><anno>Bytes</anno></c> is the total number of bytes
	read from the port.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="4"/>
      <fsummary>Information about the links of a port</fsummary>
      <desc>
	<p><c><anno>Pids</anno></c> is a list of the process identifiers
	of the processes that the port is linked to.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="5"/>
      <fsummary>Information about the locking of a port</fsummary>
      <desc>
	<p><c><anno>Locking</anno></c> is currently either <c>false</c>
	(emulator without SMP support), <c>port_level</c> (port specific
	locking), or <c>driver_level</c> (driver specific locking). Note
	that these results are highly implementation specific and might
	change in the future.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="6"/>
      <fsummary>Information about the memory size of a port</fsummary>
      <desc>
	<p><c><anno>Bytes</anno></c> is the total amount of memory,
	in bytes, allocated for this port by the runtime system. Note
	that the port itself might have allocated memory which is not
	included in <c><anno>Bytes</anno></c>.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="7"/>
      <fsummary>Information about the monitors of a port</fsummary>
      <desc>
	<p><c><anno>Monitors</anno></c> represent processes that this port
	is monitoring.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="8"/>
      <fsummary>Information about the name of a port</fsummary>
      <desc>
	<p><c><anno>Name</anno></c> is the command name set by
	<seealso marker="#open_port/2">open_port/2</seealso>.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="9"/>
      <fsummary>Information about the OS pid of a port</fsummary>
      <desc>
	<p><c><anno>OsPid</anno></c> is the process identifier (or equivalent)
	of an OS process created with
	<seealso marker="#open_port/2">open_port({spawn | spawn_executable,
	Command}, Options)</seealso>. If the port is not the result of spawning
	an OS process, the value is <c>undefined</c>.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="10"/>
      <fsummary>Information about the output of a port</fsummary>
      <desc>
	<p><c><anno>Bytes</anno></c> is the total number of bytes written
	to the port from Erlang processes using either
	<seealso marker="#port_command/2">port_command/2</seealso>,
	<seealso marker="#port_command/3">port_command/3</seealso>,
	or <c><anno>Port</anno> ! {Owner, {command, Data}</c>.
	</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="11"/>
      <fsummary>Information about the parallelism hint of a port</fsummary>
      <desc>
	<p><c><anno>Boolean</anno></c> corresponds to the port parallelism
	hint being used by this port. For more information see
	the <seealso marker="#open_port_parallelism">parallelism</seealso>
	option of <seealso marker="#open_port/2">open_port/2</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="12"/>
      <fsummary>Information about the queue size of a port</fsummary>
      <desc>
	<p><c><anno>Bytes</anno></c> is the total amount of data,
	in bytes, queued by the port using the ERTS driver queue
	implementation.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_info" arity="2" clause_i="13"/>
      <fsummary>Information about the registered name of a port</fsummary>
      <desc>
	<p><c><anno>RegisteredName</anno></c> is the registered name of
	the port. If the port has no registered name, <c>[]</c> is returned.</p>
	<p>If the port identified by <c><anno>Port</anno></c> is not open,
	<c>undefined</c> is returned. If <c>undefined</c> is returned and
	the calling process was linked to a previously open port identified
	by <c><anno>Port</anno></c>, an exit signal due to this link
	was received by the process prior to the return from
	<c>port_info/2</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Port</anno></c> is not a local
	port identifier, or an atom.</p>
      </desc>
    </func>
    <func>
      <name name="port_to_list" arity="1"/>
      <fsummary>Text representation of a port identifier</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of the port identifier <c><anno>Port</anno></c>.</p>
        <warning>
          <p>This BIF is intended for debugging and for use in
            the Erlang operating system. It should not be used in
            application programs.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="ports" arity="0"/>
      <fsummary>All open ports</fsummary>
      <desc>
	<p>Returns a list of port identifiers corresponding to all the
	ports currently existing on the local node.</p>

	<p>Note that a port that is exiting, exists but is not open.</p>
      </desc>
    </func>
    <func>
      <name name="pre_loaded" arity="0"/>
      <fsummary>List of all pre-loaded modules</fsummary>
      <desc>
        <p>Returns a list of Erlang modules which are pre-loaded in
          the system. As all loading of code is done through the file
          system, the file system must have been loaded previously.
          Hence, at least the module <c>init</c> must be pre-loaded.</p>
      </desc>
    </func>
    <func>
      <name name="process_display" arity="2"/>
      <fsummary>Write information about a local process on standard error</fsummary>
      <desc>
        <p>Writes information about the local process <c><anno>Pid</anno></c> on
          standard error. The currently allowed value for the atom
          <c><anno>Type</anno></c> is <c>backtrace</c>, which shows the contents of
          the call stack, including information about the call chain, with
          the current function printed first. The format of the output
          is not further defined.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="1"/>
      <fsummary>Set process flag trap_exit for the calling process</fsummary>
      <desc>
        <p>When <c>trap_exit</c> is set to <c>true</c>, exit signals
          arriving to a process are converted to <c>{'EXIT', From, Reason}</c> messages, which can be received as ordinary
          messages. If <c>trap_exit</c> is set to <c>false</c>, the
          process exits if it receives an exit signal other than
          <c>normal</c> and the exit signal is propagated to its
          linked processes. Application processes should normally
          not trap exits.</p>
        <p>Returns the old value of the flag.</p>
        <p>See also <seealso marker="#exit/2">exit/2</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="2"/>
      <fsummary>Set process flag error_handler for the calling process</fsummary>
      <desc>
        <p>This is used by a process to redefine the error handler
          for undefined function calls and undefined registered
          processes.  Inexperienced users should not use this flag
          since code auto-loading is dependent on the correct
          operation of the error handling module.</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="3"/>
      <fsummary>Set process flag min_heap_size for the calling process</fsummary>
      <desc>
        <p>This changes the minimum heap size for the calling
          process.</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="4"/>
      <fsummary>Set process flag min_bin_vheap_size for the calling process</fsummary>
      <desc>
        <p>This changes the minimum binary virtual heap size for the calling
          process.</p>
        <p>Returns the old value of the flag.</p>      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="5"/>
      <type name="priority_level"/>
      <fsummary>Set process flag priority for the calling process</fsummary>
      <desc>
        <p><marker id="process_flag_priority"></marker>
          This sets the process priority. <c><anno>Level</anno></c> is an atom.
          There are currently four priority levels: <c>low</c>,
          <c>normal</c>, <c>high</c>, and <c>max</c>. The default
          priority level is <c>normal</c>. <em>NOTE</em>: The
          <c>max</c> priority level is reserved for internal use in
          the Erlang runtime system, and should <em>not</em> be used
          by others.
        </p>
        <p>Internally in each priority level processes are scheduled
          in a round robin fashion.
        </p>
        <p>Execution of processes on priority <c>normal</c> and
          priority <c>low</c> will be interleaved. Processes on
          priority <c>low</c> will be selected for execution less
          frequently than processes on priority <c>normal</c>.
        </p>
        <p>When there are runnable processes on priority <c>high</c>
          no processes on priority <c>low</c>, or <c>normal</c> will
          be selected for execution. Note, however, that this does
          <em>not</em> mean that no processes on priority <c>low</c>,
          or <c>normal</c> will be able to run when there are
          processes on priority <c>high</c> running. On the runtime
          system with SMP support there might be more processes running
          in parallel than processes on priority <c>high</c>, i.e.,
          a <c>low</c>, and a <c>high</c> priority process might
          execute at the same time.
        </p>
        <p>When there are runnable processes on priority <c>max</c>
          no processes on priority <c>low</c>, <c>normal</c>, or
          <c>high</c> will be selected for execution. As with the
          <c>high</c> priority, processes on lower priorities might
          execute in parallel with processes on priority <c>max</c>.
        </p>
        <p>Scheduling is preemptive. Regardless of priority, a process
          is preempted when it has consumed more than a certain amount
          of reductions since the last time it was selected for
          execution.
        </p>
        <p><em>NOTE</em>: You should not depend on the scheduling
          to remain exactly as it is today. Scheduling, at least on
          the runtime system with SMP support, is very likely to be
          modified in the future in order to better utilize available
          processor cores.
        </p>
        <p>There is currently <em>no</em> automatic mechanism for
          avoiding priority inversion, such as priority inheritance,
          or priority ceilings. When using priorities you have
          to take this into account and handle such scenarios by
          yourself.
        </p>
        <p>Making calls from a <c>high</c> priority process into code
          that you don't have control over may cause the <c>high</c>
          priority process to wait for a processes with lower
          priority, i.e., effectively decreasing the priority of the
          <c>high</c> priority process during the call. Even if this
          isn't the case with one version of the code that you don't
          have under your control, it might be the case in a future
          version of it. This might, for example, happen if a
          <c>high</c> priority process triggers code loading, since
          the code server runs on priority <c>normal</c>.
        </p>
        <p>Other priorities than <c>normal</c> are normally not needed.
          When other priorities are used, they need to be used
          with care, especially the <c>high</c> priority <em>must</em>
          be used with care. A process on <c>high</c> priority should
          only perform work for short periods of time. Busy looping for
          long periods of time in a <c>high</c> priority process will
          most likely cause problems, since there are important servers
          in OTP running on priority <c>normal</c>.
        </p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="6"/>
      <fsummary>Set process flag save_calls for the calling process</fsummary>
      <desc>
        <p><c><anno>N</anno></c> must be an integer in the interval 0..10000.
          If <c><anno>N</anno></c> &gt; 0, call saving is made active for the
          process, which means that information about the <c><anno>N</anno></c>
          most recent global function calls, BIF calls, sends and
          receives made by the process are saved in a list, which
          can be retrieved with
          <c>process_info(Pid, last_calls)</c>. A global function
          call is one in which the module of the function is
          explicitly mentioned. Only a fixed amount of information
          is saved: a tuple <c>{Module, Function, Arity}</c> for
          function calls, and the mere atoms <c>send</c>,
          <c>'receive'</c> and <c>timeout</c> for sends and receives
          (<c>'receive'</c> when a message is received and
          <c>timeout</c> when a receive times out). If <c>N</c> = 0,
          call saving is disabled for the process, which is the
          default. Whenever the size of the call saving list is set,
          its contents are reset.</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="2" clause_i="7"/>
      <fsummary>Set process flag sensitive for the calling process</fsummary>
      <desc>
        <p>Set or clear the <c>sensitive</c> flag for the current process.
          When a process has been marked as sensitive by calling
          <c>process_flag(sensitive, true)</c>, features in the run-time
          system that can be used for examining the data and/or inner working
          of the process are silently disabled.</p>
        <p>Features that are disabled include (but are not limited to)
          the following:</p>
        <p>Tracing: Trace flags can still be set for the process, but no
          trace messages of any kind will be generated.
          (If the <c>sensitive</c> flag is turned off, trace messages will
          again be generated if there are any trace flags set.)</p>
        <p>Sequential tracing: The sequential trace token will be propagated
          as usual, but no sequential trace messages will be generated.</p>
        <p><c>process_info/1,2</c> cannot be used to read out the message
          queue or the process dictionary (both will be returned as empty lists).</p>
        <p>Stack back-traces cannot be displayed for the process.</p>
        <p>In crash dumps, the stack, messages, and the process dictionary
          will be omitted.</p>
        <p>If <c>{save_calls,N}</c> has been set for the process, no
          function calls will be saved to the call saving list.
          (The call saving list will not be cleared; furthermore, send, receive,
          and timeout events will still be added to the list.)</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="process_flag" arity="3"/>
      <fsummary>Set process flags for a process</fsummary>
      <desc>
        <p>Sets certain flags for the process <c><anno>Pid</anno></c>, in the same
          manner as
          <seealso marker="#process_flag/2">process_flag/2</seealso>.
          Returns the old value of the flag. The allowed values for
          <c><anno>Flag</anno></c> are only a subset of those allowed in
          <c>process_flag/2</c>, namely: <c>save_calls</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Pid</anno></c> is not a local process.</p>
      </desc>
    </func>
    <func>
      <name name="process_info" arity="1"/>
      <type name="process_info_result_item"/>
      <type name="priority_level"/>
      <type name="stack_item"/>
      <fsummary>Information about a process</fsummary>
      <desc>
        <p>Returns a list containing <c><anno>InfoTuple</anno></c>s with
	  miscellaneous information about the process identified by
	  <c>Pid</c>, or <c>undefined</c> if the process is not alive.
	</p>
	<p>
	  The order of the <c><anno>InfoTuple</anno></c>s is not defined, nor
	  are all the <c><anno>InfoTuple</anno></c>s mandatory. The <c><anno>InfoTuple</anno></c>s
	  part of the result may be changed without prior notice.
	  Currently <c><anno>InfoTuple</anno></c>s with the following items
	  are part of the result:
	  <c>current_function</c>, <c>initial_call</c>, <c>status</c>,
	  <c>message_queue_len</c>, <c>messages</c>, <c>links</c>,
	  <c>dictionary</c>, <c>trap_exit</c>, <c>error_handler</c>,
	  <c>priority</c>, <c>group_leader</c>, <c>total_heap_size</c>,
	  <c>heap_size</c>, <c>stack_size</c>, <c>reductions</c>, and
	  <c>garbage_collection</c>.
	  If the process identified by <c><anno>Pid</anno></c> has a registered name
	  also an <c><anno>InfoTuple</anno></c> with the item <c>registered_name</c>
	  will appear.
	</p>
	<p>See <seealso marker="#process_info/2">process_info/2</seealso>
	   for information about specific <c><anno>InfoTuple</anno></c>s.</p>
        <warning>
          <p>This BIF is intended for <em>debugging only</em>, use
	  <seealso marker="#process_info/2">process_info/2</seealso>
	  for all other purposes.
	  </p>
        </warning>
        <p>Failure: <c>badarg</c> if <c>Pid</c> is not a local process.</p>
      </desc>
    </func>
    <func>
      <name name="process_info" arity="2" clause_i="1"/>
      <name name="process_info" arity="2" clause_i="2"/>
      <type name="process_info_item"/>
      <type name="process_info_result_item"/>
      <type name="stack_item"/>
      <type name="priority_level"/>
      <fsummary>Information about a process</fsummary>
      <desc>
        <p>Returns information about the process identified by <c><anno>Pid</anno></c>
	   as specified by the <c><anno>Item</anno></c> or the <c><anno>ItemList</anno></c>, or <c>undefined</c> if the
	   process is not alive.
	</p>
	<p>If the process is alive and a single <c><anno>Item</anno></c> is given,
           the returned value is the corresponding
	   <c><anno>InfoTuple</anno></c> unless <c>Item =:= registered_name</c>
	   and the process has no registered name. In this case
	   <c>[]</c> is returned. This strange behavior is due to
	   historical reasons, and is kept for backward compatibility.
	</p>
	<p>If an  <c>ItemList</c> is given, the result is an
	   <c><anno>InfoTupleList</anno></c>. The <c><anno>InfoTuple</anno></c>s in the
	   <c><anno>InfoTupleList</anno></c> will appear with the corresponding
	   <c><anno>Item</anno></c>s in the same order as the <c><anno>Item</anno></c>s appeared
	   in the <c><anno>ItemList</anno></c>. Valid <c><anno>Item</anno></c>s may appear multiple
	   times in the <c><anno>ItemList</anno></c>.
	</p>
	 <note><p>If <c>registered_name</c> is part of an <c><anno>ItemList</anno></c>
	          and the process has no name registered a
		  <c>{registered_name, []}</c> <c><anno>InfoTuple</anno></c> <em>will</em>
		  appear in the resulting <c><anno>InfoTupleList</anno></c>. This
		  behavior is different than when a single
		  <c>Item =:= registered_name</c> is given, and than when
		  <c>process_info/1</c> is used.
	</p></note>
	<p>Currently the following <c><anno>InfoTuple</anno></c>s with corresponding
	   <c><anno>Item</anno></c>s are valid:</p>
        <taglist>
          <tag><c>{backtrace, <anno>Bin</anno>}</c></tag>
          <item>
            <p>The binary <c><anno>Bin</anno></c> contains the same information as
              the output from
              <c>erlang:process_display(<anno>Pid</anno>, backtrace)</c>. Use
              <c>binary_to_list/1</c> to obtain the string of characters
              from the binary.</p>
          </item>
          <tag><c>{binary, <anno>BinInfo</anno>}</c></tag>
          <item>
            <p><c><anno>BinInfo</anno></c> is a list containing miscellaneous information
	      about binaries currently being referred to by this process.
	      This <c><anno>InfoTuple</anno></c> may be changed or removed without prior
	      notice.</p>
          </item>
          <tag><c>{catchlevel, <anno>CatchLevel</anno>}</c></tag>
          <item>
            <p><c><anno>CatchLevel</anno></c> is the number of currently active
	    catches in this process. This <c><anno>InfoTuple</anno></c> may be
	    changed or removed without prior notice.</p>
          </item>
          <tag><c>{current_function, {<anno>Module</anno>, <anno>Function</anno>, <anno>Arity</anno>}}</c></tag>
          <item>
            <p><c><anno>Module</anno></c>, <c><anno>Function</anno></c>, <c><anno>Arity</anno></c> is
              the current function call of the process.</p>
          </item>
          <tag><c>{current_location, {<anno>Module</anno>, <anno>Function</anno>, <anno>Arity</anno>, <anno>Location</anno>}}</c></tag>
          <item>
            <p><c><anno>Module</anno></c>, <c><anno>Function</anno></c>, <c><anno>Arity</anno></c> is
              the current function call of the process.
	      <c><anno>Location</anno></c> is a list of two-tuples that describes the
	      location in the source code.
	    </p>
          </item>
          <tag><c>{current_stacktrace, <anno>Stack</anno>}</c></tag>
          <item>
            <p>Return the current call stack back-trace (<em>stacktrace</em>)
              of the process. The stack has the same format as returned by
	      <seealso marker="#get_stacktrace/0">erlang:get_stacktrace/0</seealso>.
	    </p>
          </item>
          <tag><c>{dictionary, <anno>Dictionary</anno>}</c></tag>
          <item>
            <p><c><anno>Dictionary</anno></c> is the dictionary of the process.</p>
          </item>
          <tag><c>{error_handler, <anno>Module</anno>}</c></tag>
          <item>
            <p><c><anno>Module</anno></c> is the error handler module used by
              the process (for undefined function calls, for example).</p>
          </item>
          <tag><c>{garbage_collection, <anno>GCInfo</anno>}</c></tag>
          <item>
            <p><c><anno>GCInfo</anno></c> is a list which contains miscellaneous
	       information about garbage collection for this process.
	       The content of <c><anno>GCInfo</anno></c> may be changed without
	       prior notice.</p>
          </item>
          <tag><c>{group_leader, <anno>GroupLeader</anno>}</c></tag>
          <item>
            <p><c><anno>GroupLeader</anno></c> is group leader for the IO of
              the process.</p>
          </item>
          <tag><c>{heap_size, <anno>Size</anno>}</c></tag>
          <item>
            <p><c><anno>Size</anno></c> is the size in words of youngest heap generation
	    of the process. This generation currently include the stack
	    of the process. This information is highly implementation
	    dependent, and may change if the implementation change.
	    </p>
          </item>
          <tag><c>{initial_call, {Module, Function, Arity}}</c></tag>
          <item>
            <p><c>Module</c>, <c>Function</c>, <c>Arity</c> is
              the initial function call with which the process was
              spawned.</p>
          </item>
          <tag><c>{links, <anno>PidsAndPorts</anno>}</c></tag>
          <item>
            <p><c><anno>PidsAndPorts</anno></c> is a list of pids and 
	    port identifiers, with processes or ports to which the process 
	    has a link.</p>
          </item>
          <tag><c>{last_calls, false|Calls}</c></tag>
          <item>
            <p>The value is <c>false</c> if call saving is not active
              for the process (see
              <seealso marker="#process_flag/3">process_flag/3</seealso>).
              If call saving is active, a list is returned, in which
              the last element is the most recent called.</p>
          </item>
          <tag><c>{memory, <anno>Size</anno>}</c></tag>
          <item>
            <p><c><anno>Size</anno></c> is the size in bytes of the process. This
              includes call stack, heap and internal structures.</p>
          </item>
          <tag><c>{message_queue_len, <anno>MessageQueueLen</anno>}</c></tag>
          <item>
            <p><c><anno>MessageQueueLen</anno></c> is the number of messages
              currently in the message queue of the process. This is
              the length of the list <c><anno>MessageQueue</anno></c> returned as
              the info item <c>messages</c> (see below).</p>
          </item>
          <tag><c>{messages, <anno>MessageQueue</anno>}</c></tag>
          <item>
            <p><c><anno>MessageQueue</anno></c> is a list of the messages to
              the process, which have not yet been processed.</p>
          </item>
          <tag><c>{min_heap_size, <anno>MinHeapSize</anno>}</c></tag>
          <item>
            <p><c><anno>MinHeapSize</anno></c> is the minimum heap size for the process.</p>
          </item>
          <tag><c>{min_bin_vheap_size, <anno>MinBinVHeapSize</anno>}</c></tag>
          <item>
            <p><c><anno>MinBinVHeapSize</anno></c> is the minimum binary virtual heap size for the process.</p>
          </item>
          <tag><c>{monitored_by, <anno>Pids</anno>}</c></tag>
          <item>
            <p>A list of pids that are monitoring the process (with
              <c>monitor/2</c>).</p>
          </item>
          <tag><c>{monitors, <anno>Monitors</anno>}</c></tag>
          <item>
            <p>A list of monitors (started by <c>monitor/2</c>)
              that are active for the process. For a local process
              monitor or a remote process monitor by pid, the list item
              is <c>{process, <anno>Pid</anno>}</c>, and for a remote process
              monitor by name, the list item is
              <c>{process, {<anno>RegName</anno>, <anno>Node</anno>}}</c>.</p>
          </item>
          <tag><c>{priority, Level}</c></tag>
          <item>
            <p><c><anno>Level</anno></c> is the current priority level for
	      the process. For more information on priorities see
              <seealso marker="#process_flag_priority">process_flag(priority, Level)</seealso>.</p>
          </item>
          <tag><c>{reductions, <anno>Number</anno>}</c></tag>
          <item>
            <p><c><anno>Number</anno></c> is the number of reductions executed by
              the process.</p>
          </item>
          <tag><c>{registered_name, <anno>Atom</anno>}</c></tag>
          <item>
            <p><c><anno>Atom</anno></c> is the registered name of the process. If
              the process has no registered name, this tuple is not
              present in the list.</p>
          </item>
          <tag><c>{sequential_trace_token, [] | <anno>SequentialTraceToken</anno>}</c></tag>
          <item>
            <p><c><anno>SequentialTraceToken</anno></c> the sequential trace token for
	    the process. This <c><anno>InfoTuple</anno></c> may be changed or removed
	    without prior notice.</p>
          </item>
          <tag><c>{stack_size, <anno>Size</anno>}</c></tag>
          <item>
            <p><c><anno>Size</anno></c> is the stack size of the process in words.</p>
          </item>
          <tag><c>{status, <anno>Status</anno>}</c></tag>
          <item>
            <p><c><anno>Status</anno></c> is the status of the process. <c><anno>Status</anno></c>
              is <c>exiting</c>, <c>garbage_collecting</c>,
              <c>waiting</c> (for a message), <c>running</c>,
              <c>runnable</c> (ready to run, but another process is
              running), or <c>suspended</c> (suspended on a "busy" port
              or by the <c>erlang:suspend_process/[1,2]</c> BIF).</p>
          </item>
          <tag><c>{suspending, <anno>SuspendeeList</anno>}</c></tag>
          <item>
            <p><c><anno>SuspendeeList</anno></c> is a list of <c>{<anno>Suspendee</anno>,
	    <anno>ActiveSuspendCount</anno>, <anno>OutstandingSuspendCount</anno>}</c> tuples.
	    <c><anno>Suspendee</anno></c> is the pid of a process that have been or is to
	    be suspended by the process identified by <c><anno>Pid</anno></c> via the
	    <seealso marker="#suspend_process/2">erlang:suspend_process/2</seealso>
	    BIF, or the
	    <seealso marker="#suspend_process/1">erlang:suspend_process/1</seealso>
	    BIF. <c><anno>ActiveSuspendCount</anno></c> is the number of times the
	    <c><anno>Suspendee</anno></c> has been suspended by <c><anno>Pid</anno></c>.
	    <c><anno>OutstandingSuspendCount</anno></c> is the number of not yet
	    completed suspend requests sent by <c><anno>Pid</anno></c>. That is,
	    if <c><anno>ActiveSuspendCount</anno> =/= 0</c>, <c><anno>Suspendee</anno></c> is
	    currently in the suspended state, and if
	    <c><anno>OutstandingSuspendCount</anno> =/= 0</c> the <c>asynchronous</c>
	    option of <c>erlang:suspend_process/2</c> has been used and
	    the suspendee has not yet been suspended by <c><anno>Pid</anno></c>.
	    Note that the <c><anno>ActiveSuspendCount</anno></c> and
	    <c><anno>OutstandingSuspendCount</anno></c> are not the total suspend count
	    on <c><anno>Suspendee</anno></c>, only the parts contributed by <c>Pid</c>.
	    </p>
          </item>
          <tag><c>{total_heap_size, <anno>Size</anno>}</c></tag>
          <item>
            <p><c><anno>Size</anno></c> is the total size in words of all heap
	    fragments of the process. This currently include the stack
	    of the process.
	    </p>
          </item>
          <tag><c>{trace, <anno>InternalTraceFlags</anno>}</c></tag>
          <item>
            <p><c><anno>InternalTraceFlags</anno></c> is an integer representing
	    internal trace flag for this process. This <c><anno>InfoTuple</anno></c>
	    may be changed or removed without prior notice.</p>
          </item>
          <tag><c>{trap_exit, <anno>Boolean</anno>}</c></tag>
          <item>
            <p><c><anno>Boolean</anno></c> is <c>true</c> if the process is trapping
              exits, otherwise it is <c>false</c>.</p>
          </item>
        </taglist>
        <p>Note however, that not all implementations support every one
          of the above <c><anno>Item</anno></c>s.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Pid</anno></c> is not a local process,
	or if <c><anno>Item</anno></c> is not a valid <c><anno>Item</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="processes" arity="0"/>
      <fsummary>All processes</fsummary>
      <desc>
        <p>Returns a list of process identifiers corresponding to
	   all the processes currently existing on the local node.
	</p>
	<p>Note that a process that is exiting, exists but is not alive, i.e.,
	   <c>is_process_alive/1</c> will return <c>false</c> for a process
	   that is exiting, but its process identifier will be part
	   of the result returned from <c>processes/0</c>.
	</p>
        <pre>
> <input>processes().</input>
[&lt;0.0.0&gt;,&lt;0.2.0&gt;,&lt;0.4.0&gt;,&lt;0.5.0&gt;,&lt;0.7.0&gt;,&lt;0.8.0&gt;]</pre>
      </desc>
    </func>
    <func>
      <name name="purge_module" arity="1"/>
      <fsummary>Remove old code for a module</fsummary>
      <desc>
        <p>Removes old code for <c><anno>Module</anno></c>. Before this BIF is used,
          <c>erlang:check_process_code/2</c> should be called to check
          that no processes are executing old code in the module.</p>
        <warning>
          <p>This BIF is intended for the code server (see
            <seealso marker="kernel:code">code(3)</seealso>) and should not be
            used elsewhere.</p>
        </warning>
        <p>Failure: <c>badarg</c> if there is no old code for
          <c><anno>Module</anno></c>.</p>
      </desc>
    </func>
    <func>
      <name name="put" arity="2"/>
      <fsummary>Add a new value to the process dictionary</fsummary>
      <desc>
        <p>Adds a new <c><anno>Key</anno></c> to the process dictionary, associated
          with the value <c><anno>Val</anno></c>, and returns <c>undefined</c>. If
          <c><anno>Key</anno></c> already exists, the old value is deleted and
          replaced by <c><anno>Val</anno></c> and the function returns the old value.</p>
        <note>
          <p>The values stored when <c>put</c> is evaluated within
            the scope of a <c>catch</c> will not be retracted if a
            <c>throw</c> is evaluated, or if an error occurs.</p>
        </note>
        <pre>
> <input>X = put(name, walrus), Y = put(name, carpenter),</input>
<input>Z = get(name),</input>
<input>{X, Y, Z}.</input>
{undefined,walrus,carpenter}</pre>
      </desc>
    </func>
    <func>
      <name name="raise" arity="3"/>
      <type name="raise_stacktrace"/>
      <fsummary>Stop execution with an exception of given class, reason and call stack backtrace</fsummary>
      <desc>
        <p>Stops the execution of the calling process with an
          exception of given class, reason and call stack backtrace
          (<em>stacktrace</em>).</p>
        <warning>
          <p>This BIF is intended for debugging and for use in
            the Erlang operating system. In general, it should
            be avoided in applications, unless you know
            very well what you are doing.</p>
        </warning>
        <p><c><anno>Class</anno></c> is one of <c>error</c>, <c>exit</c> or
          <c>throw</c>, so if it were not for the stacktrace
          <c>erlang:raise(<anno>Class</anno>, <anno>Reason</anno>, <anno>Stacktrace</anno>)</c> is
          equivalent to <c>erlang:<anno>Class</anno>(<anno>Reason</anno>)</c>.
          <c><anno>Reason</anno></c> is any term and <c><anno>Stacktrace</anno></c> is a list as
          returned from <c>get_stacktrace()</c>, that is a list of
          4-tuples <c>{Module, Function, Arity | Args,
          Location}</c> where <c>Module</c> and <c>Function</c>
          are atoms and the third element is an integer arity or an
          argument list. The stacktrace may also contain <c>{Fun,
          Args, Location}</c> tuples where
          <c>Fun</c> is a local fun and <c>Args</c> is an argument list.</p>
	<p>The <c>Location</c> element at the end is optional.
	  Omitting it is equivalent to specifying an empty list.</p>
        <p>The stacktrace is used as the exception stacktrace for the
          calling process; it will be truncated to the current
          maximum stacktrace depth.</p>
        <p>Because evaluating this function causes the process to
          terminate, it has no return value - unless the arguments are
          invalid, in which case the function <em>returns the error reason</em>, that is <c>badarg</c>. If you want to be
          really sure not to return you can call
          <c>error(erlang:raise(<anno>Class</anno>, <anno>Reason</anno>, <anno>Stacktrace</anno>))</c>
          and hope to distinguish exceptions later.</p>
      </desc>
    </func>
    <func>
      <name name="read_timer" arity="2"/>
      <fsummary>Read the state of a timer</fsummary>
      <desc>
        <p>
	  Read the state of a timer that has been created by either
	  <seealso marker="#start_timer/4"><c>erlang:start_timer()</c></seealso>,
	  or <seealso marker="#send_after/4"><c>erlang:send_after()</c></seealso>.
	  <c><anno>TimerRef</anno></c> identifies the timer, and
	  was returned by the BIF that created the timer.
	</p>
	<p>Currently available <c><anno>Option</anno>s</c>:</p>
        <taglist>
          <tag><c>{async, Async}</c></tag>
          <item>
	    <p>
	      Asynchronous request for state information. <c>Async</c>
	      defaults to <c>false</c> which will cause the operation
	      to be performed synchronously. In this case, the <c>Result</c>
	      will be returned by <c>erlang:read_timer()</c>. When
	      <c>Async</c> is set to <c>true</c>, <c>erlang:read_timer()</c>
	      will send an asynchronous request for the state information
	      to the timer service that manages the timer, and then return
	      <c>ok</c>. A message on the format <c>{read_timer,
	      <anno>TimerRef</anno>, <anno>Result</anno>}</c> will be
	      sent to the caller of <c>erlang:read_timer()</c> when the
	      operation has been processed.
	    </p>
	  </item>
        </taglist>
	<p>
	  More <c><anno>Option</anno></c>s may be added in the future.
	</p>
	<p>
	  When the <c><anno>Result</anno></c> equals <c>false</c>, a
	  timer corresponding to <c><anno>TimerRef</anno></c> could not
	  be found. This can be either because the timer had expired,
	  had been canceled, or because <c><anno>TimerRef</anno></c>
	  never has corresponded to a timer. If the timer has expired,
	  the timeout message has been sent, but it does not tell you
	  whether or not it has arrived at its destination yet. When the
	  <c><anno>Result</anno></c> is an integer, it represents the
	  time in milli-seconds left until the timer will expire.
	</p>
	<note>
	  <p>
	    The timer service that manages the timer may be co-located
	    with another scheduler than the scheduler that the calling
	    process is executing on. If this is the case, communication
	    with the timer service will take much longer time than if it
	    is located locally. If the calling process is in critical
	    path, and can do other things while waiting for the result
	    of this operation you want to use the <c>{async, true}</c>
	    option. If using the <c>{async, false}</c> option, the calling
	    process will be blocked until the operation has been
	    performed.
	  </p>
	</note>
        <p>See also 
          <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>,
          <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>,
          and
          <seealso marker="#cancel_timer/2"><c>erlang:cancel_timer/2</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="read_timer" arity="1"/>
      <fsummary>Read the state of a timer</fsummary>
      <desc>
        <p>Read the state of a timer. The same as calling
	<seealso marker="#read_timer/2"><c>erlang:read_timer(TimerRef,
	[])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="ref_to_list" arity="1"/>
      <fsummary>Text representation of a reference</fsummary>
      <desc>
        <p>Returns a string which corresponds to the text
          representation of <c><anno>Ref</anno></c>.</p>
        <warning>
          <p>This BIF is intended for debugging and for use in
            the Erlang operating system. It should not be used in
            application programs.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="register" arity="2"/>
      <fsummary>Register a name for a pid (or port)</fsummary>
      <desc>
        <p>Associates the name <c><anno>RegName</anno></c> with a pid or a port
          identifier. <c><anno>RegName</anno></c>, which must be an atom, can be used
          instead of the pid / port identifier in the send operator
          (<c><anno>RegName</anno> ! Message</c>).</p>
        <pre>
> <input>register(db, Pid).</input>
true</pre>
        <p>Failure: <c>badarg</c> if <c><anno>PidOrPort</anno></c> is not an existing,
          local process or port, if <c><anno>RegName</anno></c> is already in use,
          if the process or port is already registered (already has a
          name), or if <c><anno>RegName</anno></c> is the atom <c>undefined</c>.</p>
      </desc>
    </func>
    <func>
      <name name="registered" arity="0"/>
      <fsummary>All registered names</fsummary>
      <desc>
        <p>Returns a list of names which have been registered using
          <seealso marker="#register/2">register/2</seealso>.</p>
        <pre>
> <input>registered().</input>
[code_server, file_server, init, user, my_db]</pre>
      </desc>
    </func>
    <func>
      <name name="resume_process" arity="1"/>
      <fsummary>Resume a suspended process</fsummary>
      <desc>
        <p>Decreases the suspend count on the process identified by
	<c><anno>Suspendee</anno></c>. <c><anno>Suspendee</anno></c> should previously have been
	suspended via
	<seealso marker="#suspend_process/2">erlang:suspend_process/2</seealso>,
	or
	<seealso marker="#suspend_process/1">erlang:suspend_process/1</seealso>
	by the process calling <c>erlang:resume_process(<anno>Suspendee</anno>)</c>. When
	the suspend count on <c><anno>Suspendee</anno></c> reach zero, <c><anno>Suspendee</anno></c>
	will be resumed, i.e., the state of the <c>Suspendee</c> is changed
	from suspended into the state <c><anno>Suspendee</anno></c> was in before it was
	suspended.
	</p>
        <warning>
          <p>This BIF is intended for debugging only.</p>
        </warning>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	  If <c><anno>Suspendee</anno></c> isn't a process identifier.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If the process calling <c>erlang:resume_process/1</c> had
	  not previously increased the suspend count on the process
	  identified by <c><anno>Suspendee</anno></c>.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If the process identified by <c><anno>Suspendee</anno></c> is not alive.
	  </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="round" arity="1"/>
      <fsummary>Return an integer by rounding a number</fsummary>
      <desc>
        <p>Returns an integer by rounding <c><anno>Number</anno></c>.</p>
        <pre>
> <input>round(5.5).</input>
6</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="self" arity="0"/>
      <fsummary>Pid of the calling process</fsummary>
      <desc>
        <p>Returns the pid (process identifier) of the calling process.</p>
        <pre>
> <input>self().</input>
&lt;0.26.0></pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="send" arity="2"/>
      <fsummary>Send a message</fsummary>
      <type name="dst"/>
      <desc>
        <p>Sends a message and returns <c><anno>Msg</anno></c>. This is the same as
          <c><anno>Dest</anno> ! <anno>Msg</anno></c>.</p>
        <p><c><anno>Dest</anno></c> may be a remote or local pid, a (local) port, a
          locally registered name, or a tuple <c>{<anno>RegName</anno>, <anno>Node</anno>}</c>
          for a registered name at another node.</p>
      </desc>
    </func>
    <func>
      <name name="send" arity="3"/>
      <type name="dst"/>
      <fsummary>Send a message conditionally</fsummary>
      <desc>
        <p>Sends a message and returns <c>ok</c>, or does not send
          the message but returns something else (see below). Otherwise
          the same as
          <seealso marker="#send/2">erlang:send/2</seealso>. See
          also
          <seealso marker="#send_nosuspend/2">erlang:send_nosuspend/2,3</seealso>.
          for more detailed explanation and warnings.</p>
        <p>The possible options are:</p>
        <taglist>
          <tag><c>nosuspend</c></tag>
          <item>
            <p>If the sender would have to be suspended to do the send,
              <c>nosuspend</c> is returned instead.</p>
          </item>
          <tag><c>noconnect</c></tag>
          <item>
            <p>If the destination node would have to be auto-connected
              before doing the send, <c>noconnect</c> is returned
              instead.</p>
          </item>
        </taglist>
        <warning>
          <p>As with <c>erlang:send_nosuspend/2,3</c>: Use with extreme
            care!</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="send_after" arity="4"/>
      <fsummary>Start a timer</fsummary>
      <desc>
        <p>
	  Starts a timer. When the timer expires, the message
          <c><anno>Msg</anno></c> will be sent to the process
	  identified by <c><anno>Dest</anno></c>. Appart from
	  the format of the message sent to
	  <c><anno>Dest</anno></c> when the timer expires
	  <c>erlang:send_after/4</c> works exactly as
	  <seealso marker="#start_timer/4"><c>erlang:start_timer/4</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="send_after" arity="3"/>
      <fsummary>Start a timer</fsummary>
      <desc>
        <p>Starts a timer. The same as calling
	<seealso marker="#send_after/4"><c>erlang:send_after(<anno>Time</anno>,
	<anno>Dest</anno>, <anno>Msg</anno>, [])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="send_nosuspend" arity="2"/>
      <fsummary>Try to send a message without ever blocking</fsummary>
      <type name="dst"/>
      <desc>
        <p>The same as
          <seealso marker="#send/3">erlang:send(<anno>Dest</anno>, <anno>Msg</anno>, [nosuspend])</seealso>, but returns <c>true</c> if
          the message was sent and <c>false</c> if the message was not
          sent because the sender would have had to be suspended.</p>
        <p>This function is intended for send operations towards an
          unreliable remote node without ever blocking the sending
          (Erlang) process. If the connection to the remote node
          (usually not a real Erlang node, but a node written in C or
          Java) is overloaded, this function <em>will not send the message</em> but return <c>false</c> instead.</p>
        <p>The same happens, if <c><anno>Dest</anno></c> refers to a local port that
          is busy. For all other destinations (allowed for the ordinary
          send operator <c>'!'</c>) this function sends the message and
          returns <c>true</c>.</p>
        <p>This function is only to be used in very rare circumstances
          where a process communicates with Erlang nodes that can
          disappear without any trace causing the TCP buffers and
          the drivers queue to be over-full before the node will actually
          be shut down (due to tick timeouts) by <c>net_kernel</c>. The
          normal reaction to take when this happens is some kind of
          premature shutdown of the other node.</p>
        <p>Note that ignoring the return value from this function would
          result in <em>unreliable</em> message passing, which is
          contradictory to the Erlang programming model. The message is
          <em>not</em> sent if this function returns <c>false</c>.</p>
        <p>Note also that in many systems, transient states of
          overloaded queues are normal. The fact that this function
          returns <c>false</c> does not in any way mean that the other
          node is guaranteed to be non-responsive, it could be a
          temporary overload. Also a return value of <c>true</c> does
          only mean that the message could be sent on the (TCP) channel
          without blocking, the message is not guaranteed to have
          arrived at the remote node. Also in the case of a disconnected
          non-responsive node, the return value is <c>true</c> (mimics
          the behaviour of the <c>!</c> operator). The expected
          behaviour as well as the actions to take when the function
          returns <c>false</c> are application and hardware specific.</p>
        <warning>
          <p>Use with extreme care!</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="send_nosuspend" arity="3"/>
      <fsummary>Try to send a message without ever blocking</fsummary>
      <type name="dst"/>
      <desc>
        <p>The same as
          <seealso marker="#send/3">erlang:send(<anno>Dest</anno>, <anno>Msg</anno>, [nosuspend | <anno>Options</anno>])</seealso>,
          but with boolean return value.</p>
        <p>This function behaves like
          <seealso marker="#send_nosuspend/2">erlang:send_nosuspend/2)</seealso>,
          but takes a third parameter, a list of options. The only
          currently implemented option is <c>noconnect</c>. The option
          <c>noconnect</c> makes the function return <c>false</c> if
          the remote node is not currently reachable by the local
          node. The normal behaviour is to try to connect to the node,
          which may stall the process for a shorter period. The use of
          the <c>noconnect</c> option makes it possible to be
          absolutely sure not to get even the slightest delay when
          sending to a remote process. This is especially useful when
          communicating with nodes who expect to always be
          the connecting part (i.e. nodes written in C or Java).</p>
        <p>Whenever the function returns <c>false</c> (either when a
          suspend would occur or when <c>noconnect</c> was specified and
          the node was not already connected), the message is guaranteed
          <em>not</em> to have been sent.</p>
        <warning>
          <p>Use with extreme care!</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="set_cookie" arity="2"/>
      <fsummary>Set the magic cookie of a node</fsummary>
      <desc>
        <p>Sets the magic cookie of <c><anno>Node</anno></c> to the atom
          <c><anno>Cookie</anno></c>. If <c><anno>Node</anno></c> is the local node, the function
          also sets the cookie of all other unknown nodes to
          <c><anno>Cookie</anno></c> (see
          <seealso marker="doc/reference_manual:distributed">Distributed Erlang</seealso> in the Erlang Reference Manual).</p>
        <p>Failure: <c>function_clause</c> if the local node is not
          alive.</p>
      </desc>
    </func>
    <func>
      <name name="setelement" arity="3"/>
      <type_desc variable="Index">1..tuple_size(<anno>Tuple1</anno>)</type_desc>
      <fsummary>Set Nth element of a tuple</fsummary>
      <desc>
        <p>Returns a tuple which is a copy of the argument <c><anno>Tuple1</anno></c>
          with the element given by the integer argument <c><anno>Index</anno></c>
          (the first element is the element with index 1) replaced by
          the argument <c><anno>Value</anno></c>.</p>
        <pre>
> <input>setelement(2, {10, green, bottles}, red).</input>
{10,red,bottles}</pre>
      </desc>
    </func>
    <func>
      <name name="size" arity="1"/>
      <fsummary>Size of a tuple or binary</fsummary>
      <desc>
        <p>Returns an integer which is the size of the argument
          <c><anno>Item</anno></c>,  which must be either a tuple or a binary.</p>
        <pre>
> <input>size({morni, mulle, bwange}).</input>
3</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="spawn" arity="1"/>
      <fsummary>Create a new process with a fun as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list <c>[]</c>. Otherwise works
          like <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn" arity="2"/>
      <fsummary>Create a new process with a fun as entry point on a given node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list <c>[]</c> on <c><anno>Node</anno></c>. If
          <c><anno>Node</anno></c> does not exist, a useless pid is returned.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn" arity="3"/>
      <fsummary>Create a new process with a function as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c>. The new process
          created will be placed in the system scheduler queue and be
          run some time later.</p>
        <p><c>error_handler:undefined_function(<anno>Module</anno>, <anno>Function</anno>, <anno>Args</anno>)</c> is evaluated by the new process if
          <c><anno>Module</anno>:<anno>Function</anno>/Arity</c> does not exist (where
          <c>Arity</c> is the length of <c><anno>Args</anno></c>). The error handler
          can be redefined (see
          <seealso marker="#process_flag/2">process_flag/2</seealso>).
          If <c>error_handler</c> is undefined, or the user has
          redefined the default <c>error_handler</c> its replacement is
          undefined, a failure with the reason <c>undef</c> will occur.</p>
        <pre>
> <input>spawn(speed, regulator, [high_speed, thin_cut]).</input>
&lt;0.13.1></pre>
      </desc>
    </func>
    <func>
      <name name="spawn" arity="4"/>
      <fsummary>Create a new process with a function as entry point on a given node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c> on <c>Node</c>. If
          <c><anno>Node</anno></c> does not exists, a useless pid is returned.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_link" arity="1"/>
      <fsummary>Create and link to a new process with a fun as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list []. A link is created between
          the calling process and the new process, atomically.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_link" arity="2"/>
      <fsummary>Create and link to a new process with a fun as entry point on a specified node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list [] on <c><anno>Node</anno></c>. A link is
          created between the calling process and the new process,
          atomically. If <c><anno>Node</anno></c> does not exist, a useless pid is
          returned (and due to the link, an exit signal with exit
          reason <c>noconnection</c> will be received). Otherwise works
          like <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_link" arity="3"/>
      <fsummary>Create and link to a new process with a function as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c>. A link is created
          between the calling process and the new process, atomically.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_link" arity="4"/>
      <fsummary>Create and link to a new process with a function as entry point on a given node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c> on <c>Node</c>. A
          link is created between the calling process and the new
          process, atomically. If <c><anno>Node</anno></c> does not exist, a useless
          pid is returned (and due to the link, an exit signal with exit
          reason <c>noconnection</c> will be received). Otherwise works
          like <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_monitor" arity="1"/>
      <fsummary>Create and monitor a new process with a fun as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list [] and reference for a monitor
          created to the new process.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_monitor" arity="3"/>
      <fsummary>Create and monitor a new process with a function as entry point</fsummary>
      <desc>
        <p>A new process is started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c>, and the process is
          monitored at the same time. Returns the pid and a reference
          for the monitor.
          Otherwise works like
          <seealso marker="#spawn/3">spawn/3</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_opt" arity="2"/>
      <type name="priority_level" />
      <fsummary>Create a new process with a fun as entry point</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list <c>[]</c>. Otherwise
          works like
          <seealso marker="#spawn_opt/4">spawn_opt/4</seealso>.</p>
        <p>If the option <c>monitor</c> is given, the newly created
          process will be monitored and both the pid and reference for
          the monitor will be returned.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_opt" arity="3"/>
      <type name="priority_level" />
      <fsummary>Create a new process with a fun as entry point on a given node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Fun</anno></c> to the empty list <c>[]</c> on <c><anno>Node</anno></c>. If
          <c><anno>Node</anno></c> does not exist, a useless pid is returned.
          Otherwise works like
          <seealso marker="#spawn_opt/4">spawn_opt/4</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="spawn_opt" arity="4"/>
      <type name="priority_level" />
      <fsummary>Create a new process with a function as entry point</fsummary>
      <desc>
        <p>Works exactly like
          <seealso marker="#spawn/3">spawn/3</seealso>, except that an
          extra option list is given when creating the process.</p>
        <p>If the option <c>monitor</c> is given, the newly created
          process will be monitored and both the pid and reference for
          the monitor will be returned.</p>
        <taglist>
          <tag><c>link</c></tag>
          <item>
            <p>Sets a link to the parent process (like
              <c>spawn_link/3</c> does).</p>
          </item>
          <tag><c>monitor</c></tag>
          <item>
            <p>Monitor the new process (just like
              <seealso marker="#monitor/2">monitor/2</seealso> does).</p>
          </item>
          <tag><c>{priority, <anno>Level</anno>}</c></tag>
          <item>
            <p>Sets the priority of the new process. Equivalent to
              executing
              <seealso marker="#process_flag_priority">process_flag(priority, <anno>Level</anno>)</seealso> in the start function of the new process,
              except that the priority will be set before the process is
              selected for execution for the first time. For more information
              on priorities see
              <seealso marker="#process_flag_priority">process_flag(priority, Level)</seealso>.</p>
          </item>
          <tag><c>{fullsweep_after, <anno>Number</anno>}</c></tag>
          <item>
            <p>This option is only useful for performance tuning.
              In general, you should not use this option unless you
              know that there is problem with execution times and/or
              memory consumption, and you should measure to make sure
              that the option improved matters.
              </p>
            <p>The Erlang runtime system uses a generational garbage
              collection scheme, using an "old heap" for data that has
              survived at least one garbage collection. When there is
              no more room on the old heap, a fullsweep garbage
              collection will be done.</p>
            <p>The <c>fullsweep_after</c> option makes it possible to
              specify the maximum number of generational collections
              before forcing a fullsweep even if there is still room on
              the old heap. Setting the number to zero effectively
              disables the general collection algorithm, meaning that
              all live data is copied at every garbage collection.</p>
            <p>Here are a few cases when it could be useful to change
              <c>fullsweep_after</c>. Firstly, if binaries that are no
              longer used should be thrown away as soon as possible.
              (Set <c><anno>Number</anno></c> to zero.) Secondly, a process that
              mostly have short-lived data will be fullsweeped seldom
              or never, meaning that the old heap will contain mostly
              garbage. To ensure a fullsweep once in a while, set
              <c><anno>Number</anno></c> to a suitable value such as 10 or 20.
              Thirdly, in embedded systems with limited amount of RAM
              and no virtual memory, one might want to preserve memory
              by setting <c><anno>Number</anno></c> to zero. (The value may be set
              globally, see
              <seealso marker="#system_flag/2">erlang:system_flag/2</seealso>.)</p>
          </item>
          <tag><c>{min_heap_size, <anno>Size</anno>}</c></tag>
          <item>
            <p>This option is only useful for performance tuning.
              In general, you should not use this option unless you
              know that there is problem with execution times and/or
              memory consumption, and you should measure to make sure
              that the option improved matters.
              </p>
            <p>Gives a minimum heap size in words. Setting this value
              higher than the system default might speed up some
              processes because less garbage collection is done.
              Setting too high value, however, might waste memory and
              slow down the system due to worse data locality.
              Therefore, it is recommended to use this option only for
              fine-tuning an application and to measure the execution
              time with various <c><anno>Size</anno></c> values.</p>
          </item>
          <tag><c>{min_bin_vheap_size, <anno>VSize</anno>}</c></tag>
          <item>
            <p>This option is only useful for performance tuning.
              In general, you should not use this option unless you
              know that there is problem with execution times and/or
              memory consumption, and you should measure to make sure
              that the option improved matters.
              </p>
	      <p>Gives a minimum binary virtual heap size in words. Setting this value
              higher than the system default might speed up some
              processes because less garbage collection is done.
              Setting too high value, however, might waste memory.
              Therefore, it is recommended to use this option only for
              fine-tuning an application and to measure the execution
              time with various <c><anno>VSize</anno></c> values.</p>
          </item>

        </taglist>
      </desc>
    </func>
    <func>
      <name name="spawn_opt" arity="5"/>
      <type name="priority_level" />
      <fsummary>Create a new process with a function as entry point on a given node</fsummary>
      <desc>
        <p>Returns the pid of a new process started by the application
          of <c><anno>Module</anno>:<anno>Function</anno></c> to <c><anno>Args</anno></c> on <c>Node</c>. If
          <c><anno>Node</anno></c> does not exist, a useless pid is returned.
          Otherwise works like
          <seealso marker="#spawn_opt/4">spawn_opt/4</seealso>.</p>
	  <note><p>The <c>monitor</c> option is currently not supported by
	  <c>spawn_opt/5</c>.</p></note>
      </desc>
    </func>
    <func>
      <name name="split_binary" arity="2"/>
      <type_desc variable="Pos">0..byte_size(Bin)</type_desc>
      <fsummary>Split a binary into two</fsummary>
      <desc>
        <p>Returns a tuple containing the binaries which are the result
          of splitting <c><anno>Bin</anno></c> into two parts at position <c><anno>Pos</anno></c>.
          This is not a destructive operation. After the operation,
          there will be three binaries altogether.</p>
        <pre>
> <input>B = list_to_binary("0123456789").</input>
&lt;&lt;"0123456789">>
> <input>byte_size(B).</input>
10
> <input>{B1, B2} = split_binary(B,3).</input>
{&lt;&lt;"012">>,&lt;&lt;"3456789">>}
> <input>byte_size(B1).</input>
3
> <input>byte_size(B2).</input>
7</pre>
      </desc>
    </func>
    <func>
      <name name="start_timer" arity="4"/>
      <fsummary>Start a timer</fsummary>
      <desc>
        <p>
	  Starts a timer. When the timer expires, the message
          <c>{timeout, <anno>TimerRef</anno>, <anno>Msg</anno>}</c>
	  will be sent to the process identified by
	  <c><anno>Dest</anno></c>.
	</p>
	<p>Currently available <c><anno>Option</anno></c>s:</p>
        <taglist>
          <tag><c>{abs, Abs}</c></tag>
          <item>
	    <p>
	      Absolute <c><anno>Time</anno></c> value. <c>Abs</c>
	      defaults to <c>false</c> which means that the
	      <c><anno>Time</anno></c> value will be interpreted
	      as a time in milli-seconds relative current
	      <seealso marker="time_correction#Erlang_Monotonic_Time">Erlang
	      monotonic time</seealso>. When <c>Abs</c> is set to
	      <c>true</c>, the <c><anno>Time</anno></c> value will
	      be interpreted as an absolute Erlang monotonic time of
	      milli-seconds
	      <seealso marker="#type_time_unit">time unit</seealso>.
	    </p>
	  </item>
        </taglist>
	<p>
	  More <c><anno>Option</anno></c>s may be added in the future.
	</p>
	<p>
	  The absolute point in time that the timer is set to expire on
	  has to be in the interval
	  <c>[</c><seealso marker="#system_info_start_time"><c>erlang:system_info(start_time)</c></seealso><c>,
	  </c><seealso marker="#system_info_end_time"><c>erlang:system_info(end_time)</c></seealso><c>]</c>.
	  Further, if a relative time is specified, the <c><anno>Time</anno></c> value
	  is not allowed to be negative.
	</p>
	<p>
	  If <c><anno>Dest</anno></c> is a <c>pid()</c>, it has to
	  be a <c>pid()</c> of a process created on the current
	  runtime system instance. This process may or may not
	  have terminated. If <c><anno>Dest</anno></c> is an
	  <c>atom()</c>, it will be interpreted as the name of a
	  locally registered process. The process referred to by the
	  name is looked up at the time of timer expiration. No error
	  is given if the name does not refer to a process.
	</p>
        <p>
	  If <c><anno>Dest</anno></c> is a <c>pid()</c>, the timer will
	  be automatically canceled if the process referred to by the
	  <c>pid()</c> is not alive, or when the process exits. This
	  feature was introduced in erts version 5.4.11. Note that
	  timers will not be automatically canceled when
	  <c><anno>Dest</anno></c> is an <c>atom()</c>.
	</p>
        <p>See also
          <seealso marker="#send_after/4"><c>erlang:send_after/4</c></seealso>,
          <seealso marker="#cancel_timer/2"><c>erlang:cancel_timer/2</c></seealso>,
          and
          <seealso marker="#read_timer/2"><c>erlang:read_timer/2</c></seealso>.</p>
        <p>Failure: <c>badarg</c> if the arguments does not satisfy
          the requirements specified above.</p>
      </desc>
    </func>
    <func>
      <name name="start_timer" arity="3"/>
      <fsummary>Start a timer</fsummary>
      <desc>
        <p>Starts a timer. The same as calling
	<seealso marker="#start_timer/4"><c>erlang:start_timer(<anno>Time</anno>,
	<anno>Dest</anno>, <anno>Msg</anno>, [])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="1"/>
      <fsummary>Information about context switches</fsummary>
      <desc>
        <p><c><anno>ContextSwitches</anno></c> is the total number of context
          switches since the system started.</p>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="2"/>
      <fsummary>Information about exact reductions</fsummary>
      <desc>
        <marker id="statistics_exact_reductions"></marker>
			<note><p><c>statistics(exact_reductions)</c> is
					a more expensive operation than
					<seealso marker="#statistics_reductions">statistics(reductions)</seealso>
					especially on an Erlang machine with SMP support.</p>
			</note>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="3"/>
      <fsummary>Information about garbage collection</fsummary>
      <desc>
        <p>This information may not be valid for all implementations.</p>
	  <pre>
> <input>statistics(garbage_collection).</input>
{85,23961,0}
</pre>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="4"/>
      <fsummary>Information about io</fsummary>
      <desc>
        <p><c><anno>Input</anno></c> is the total number of bytes received
          through ports, and <c><anno>Output</anno></c> is the total number of
          bytes output to ports.</p>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="5"/>
      <fsummary>Information about reductions</fsummary>
      <desc>
        <marker id="statistics_reductions"></marker>
			<note>
				<p>Since erts-5.5 (OTP release R11B)
					this value does not include reductions performed in current
					time slices of currently scheduled processes. If an
					exact value is wanted, use
					<seealso marker="#statistics_exact_reductions">statistics(exact_reductions)</seealso>.</p>
			</note>
        <pre>
> <input>statistics(reductions).</input>
{2046,11}
</pre>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="6"/>
      <fsummary>Information about the run-queue</fsummary>
      <desc>
        <p>Returns the total length of the run queues, that is, the number
          of processes that are ready to run on all available run queues.</p>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="7"/>
      <fsummary>Information about run-time</fsummary>
      <desc>
        <p>Note that the run-time is the sum of the run-time for all
        threads in the Erlang run-time system and may therefore be greater
        than the wall-clock time. The time is returned in milliseconds.</p>
        <pre>
> <input>statistics(runtime).</input>
{1690,1620}
</pre>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="8"/>
      <fsummary>Information about each schedulers work time</fsummary>
      <desc>
		  <marker id="statistics_scheduler_wall_time"></marker>
		  <p>
			  Returns a list of tuples with <c>{<anno>SchedulerId</anno>,
				  <anno>ActiveTime</anno>, <anno>TotalTime</anno>}</c>, where
			  <c>SchedulerId</c> is an integer id of the scheduler, <c>ActiveTime</c> is
			  the duration the scheduler has been busy, <c>TotalTime</c> is the total time duration since
			  <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso>
			  activation. The time unit is not defined and may be subject to change
			  between releases, operating systems and system restarts.
			  <c>scheduler_wall_time</c> should only be used to calculate relative
			  values for scheduler-utilization. <c>ActiveTime</c> can never exceed <c>TotalTime</c>.
		  </p>

		  <p>The definition of a busy scheduler is when it is not idle or not
			  scheduling (selecting) a process or port, meaning; executing process
			  code, executing linked-in-driver or NIF code, executing
			  built-in-functions or any other runtime handling, garbage collecting
			  or handling any other memory management. Note, a scheduler may also be
			  busy even if the operating system has scheduled out the scheduler
			  thread.
		  </p>

		  <p>
			  Returns <c>undefined</c> if the system flag
			  <seealso marker="#system_flag_scheduler_wall_time">scheduler_wall_time</seealso>
			  is turned off.
		  </p>

		  <p>The list of scheduler information is unsorted and may appear in different order
			  between calls.
		  </p>
		  <p>Using <c>scheduler_wall_time</c> to calculate scheduler utilization.</p>
<pre>
> <input>erlang:system_flag(scheduler_wall_time, true).</input>
false
> <input>Ts0 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input>
ok
</pre>
		<p>Some time later we will take another snapshot and calculate scheduler-utilization per scheduler.</p>
<pre>
> <input>Ts1 = lists:sort(erlang:statistics(scheduler_wall_time)), ok.</input>
ok
> <input>lists:map(fun({{I, A0, T0}, {I, A1, T1}}) ->
	{I, (A1 - A0)/(T1 - T0)} end, lists:zip(Ts0,Ts1)).</input>
[{1,0.9743474730177548},
 {2,0.9744843782751444},
 {3,0.9995902361669045},
 {4,0.9738012596572161},
 {5,0.9717956667018103},
 {6,0.9739235846420741},
 {7,0.973237033077876},
 {8,0.9741297293248656}]
</pre>
		<p>Using the same snapshots to calculate a total scheduler-utilization.</p>
<pre>
> <input>{A, T} = lists:foldl(fun({{_, A0, T0}, {_, A1, T1}}, {Ai,Ti}) ->
	{Ai + (A1 - A0), Ti + (T1 - T0)} end, {0, 0}, lists:zip(Ts0,Ts1)), A/T.</input>
0.9769136803764825
</pre>
        <note>
          <p><c>scheduler_wall_time</c> is by default disabled. Use <c>erlang:system_flag(scheduler_wall_time, true)</c> to enable it. </p>
        </note>
      </desc>
    </func>
    <func>
      <name name="statistics" arity="1" clause_i="9"/>
      <fsummary>Information about wall-clock</fsummary>
      <desc>
        <p><c>wall_clock</c> can be used in the same manner as
          <c>runtime</c>, except that real time is measured as
          opposed to runtime or CPU time.</p>
      </desc>
    </func>
    <func>
      <name name="suspend_process" arity="2"/>
      <fsummary>Suspend a process</fsummary>
      <desc>
        <p>Increases the suspend count on the process identified by
	<c><anno>Suspendee</anno></c> and puts it in the suspended state if it isn't
	already in the suspended state. A suspended process will not be
	scheduled for execution until the process has been resumed.
	</p>

	<p>A process can be suspended by multiple processes and can
	be suspended multiple times by a single process. A suspended
	process will not leave the suspended state until its suspend 
	count reach zero. The suspend count of <c><anno>Suspendee</anno></c>
	is decreased when
	<seealso marker="#resume_process/1">erlang:resume_process(<anno>Suspendee</anno>)</seealso>
	is called by the same process that called
	<c>erlang:suspend_process(<anno>Suspendee</anno>)</c>. All increased suspend
	counts on other processes acquired by a process will automatically be
	decreased when the process terminates.</p>

	<p>Currently the following options (<c><anno>Opt</anno></c>s) are available:</p>
        <taglist>
          <tag><c>asynchronous</c></tag>
          <item>
	  A suspend request is sent to the process identified by
	  <c><anno>Suspendee</anno></c>. <c><anno>Suspendee</anno></c> will eventually suspend
	  unless it is resumed before it was able to suspend. The caller
	  of <c>erlang:suspend_process/2</c> will return immediately,
	  regardless of whether the <c><anno>Suspendee</anno></c> has suspended yet
	  or not. Note that the point in time when the <c><anno>Suspendee</anno></c>
	  will actually suspend cannot be deduced from other events
	  in the system. The only guarantee given is that the
	  <c><anno>Suspendee</anno></c> will <em>eventually</em> suspend (unless it
	  is resumed). If the <c>asynchronous</c> option has <em>not</em>
	  been passed, the caller of <c>erlang:suspend_process/2</c> will
	  be blocked until the <c><anno>Suspendee</anno></c> has actually suspended.
	  </item>
          <tag><c>unless_suspending</c></tag>
          <item>
	  The process identified by <c><anno>Suspendee</anno></c> will be suspended
	  unless the calling process already is suspending the
	  <c><anno>Suspendee</anno></c>. If <c>unless_suspending</c> is combined
	  with the <c>asynchronous</c> option, a suspend request will be
	  sent unless the calling process already is suspending the
	  <c><anno>Suspendee</anno></c> or if a suspend request already has been sent
	  and is in transit. If the calling process already is suspending
	  the <c><anno>Suspendee</anno></c>, or if combined with the <c>asynchronous</c>
	  option and a send request already is in transit,
	  <c>false</c> is returned and the suspend count on <c><anno>Suspendee</anno></c>
	  will remain unchanged.
	  </item>
        </taglist>

	<p>If the suspend count on the process identified by
	<c><anno>Suspendee</anno></c> was increased, <c>true</c> is returned; otherwise,
	<c>false</c> is returned.</p>

        <warning>
          <p>This BIF is intended for debugging only.</p>
        </warning>
        <p>Failures:</p>
        <taglist>
          <tag><c>badarg</c></tag>
          <item>
	  If <c><anno>Suspendee</anno></c> isn't a process identifier.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If the process identified by <c><anno>Suspendee</anno></c> is same the process as
	  the process calling <c>erlang:suspend_process/2</c>.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If the process identified by <c><anno>Suspendee</anno></c> is not alive.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If the process identified by <c><anno>Suspendee</anno></c> resides on another node.
	  </item>
          <tag><c>badarg</c></tag>
          <item>
	  If <c><anno>OptList</anno></c> isn't a proper list of valid <c><anno>Opt</anno></c>s.
	  </item>
          <tag><c>system_limit</c></tag>
          <item>
	  If the process identified by <c><anno>Suspendee</anno></c> has been suspended more
	  times by the calling process than can be represented by the
	  currently used internal data structures. The current system limit
	  is larger than 2 000 000 000 suspends, and it will never be less
	  than that.
	  </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="suspend_process" arity="1"/>
      <fsummary>Suspend a process</fsummary>
      <desc>
        <p>Suspends the process identified by <c><anno>Suspendee</anno></c>. The
	same as calling
	<seealso marker="#suspend_process/2">erlang:suspend_process(<anno>Suspendee</anno>, [])</seealso>. For more information see the documentation of <seealso marker="#suspend_process/2">erlang:suspend_process/2</seealso>.
	</p>
        <warning>
          <p>This BIF is intended for debugging only.</p>
        </warning>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="1"/>
      <fsummary>Set system flag backtrace_depth</fsummary>
      <desc>
        <p>Sets the maximum depth of call stack back-traces in the
          exit reason element of <c>'EXIT'</c> tuples.</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="2"/>
      <type name="cpu_topology"/>
      <type name="level_entry"/>
      <type name="level_tag"/>
      <type name="sub_level"/>
      <type name="info_list"/>
      <fsummary>Set system flag cpu_topology</fsummary>
      <desc>
        <warning>
          <p><marker id="system_flag_cpu_topology"></marker>
          This argument is <em>deprecated</em> and
          scheduled for removal in erts-5.10/OTP-R16. Instead of using
          this argument you are advised to use the <c>erl</c> command
          line argument <seealso marker="erts:erl#+sct">+sct</seealso>.
          When this argument has been removed a final CPU topology to use
          will be determined at emulator boot time.</p>
        </warning>
        <p>Sets the user defined <c><anno>CpuTopology</anno></c>. The user defined
           CPU topology will override any automatically detected
           CPU topology. By passing <c>undefined</c> as <c><anno>CpuTopology</anno></c>
           the system will revert back to the CPU topology automatically
           detected. The returned value equals the value returned
           from <c>erlang:system_info(cpu_topology)</c> before the
           change was made.
        </p>
        <p>Returns the old value of the flag.</p>
        <p>The CPU topology is used when binding schedulers to logical
           processors. If schedulers are already bound when the CPU
           topology is changed, the schedulers will be sent a request
           to rebind according to the new CPU topology.
        </p>
        <p>The user defined CPU topology can also be set by passing
           the <seealso marker="erts:erl#+sct">+sct</seealso> command
           line argument to <c>erl</c>.
        </p>
        <p>For information on the <c><anno>CpuTopology</anno></c> type
           and more, see the documentation of
           <seealso marker="#system_info_cpu_topology">erlang:system_info(cpu_topology)</seealso>,
           and the <c>erl</c> <seealso marker="erts:erl#+sct">+sct</seealso>
           and <seealso marker="erts:erl#+sbt">+sbt</seealso>
           command line flags.
        </p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="3"/>
      <fsummary>Set system flag dirty CPU schedulers online</fsummary>
      <desc>
        <p><marker id="system_flag_dirty_cpu_schedulers_online"></marker>
        Sets the amount of dirty CPU schedulers online. Valid range is
        <![CDATA[1 <= DirtyCPUSchedulersOnline <= N]]> where <c>N</c> is the
        lesser of the return values of <c>erlang:system_info(dirty_cpu_schedulers)</c> and
        <c>erlang:system_info(schedulers_online)</c>.
        </p>
        <p>Returns the old value of the flag.</p>
        <p>Note that the number of dirty CPU schedulers online may change if the number of
        schedulers online changes. For example, if there are 12 schedulers and all are
        online, and 6 dirty CPU schedulers, all online as well, and <c>system_flag/2</c>
        is used to set the number of schedulers online to 6, then the number of dirty
        CPU schedulers online is automatically decreased by half as well, down to 3.
        Similarly, the number of dirty CPU schedulers online increases proportionally
        to increases in the number of schedulers online.</p>
        <p><em>Note that the dirty schedulers functionality is experimental</em>, and
        that you have to enable support for dirty schedulers when building OTP in order
        to try out the functionality.</p>
        <p>For more information see
        <seealso marker="#system_info_dirty_cpu_schedulers">erlang:system_info(dirty_cpu_schedulers)</seealso>
        and
        <seealso marker="#system_info_dirty_cpu_schedulers_online">erlang:system_info(dirty_cpu_schedulers_online)</seealso>.
        </p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="4"/>
      <fsummary>Set system flag fullsweep_after</fsummary>
      <desc>
        <p><c><anno>Number</anno></c> is a non-negative integer which indicates
          how many times generational garbage collections can be
          done without forcing a fullsweep collection. The value
          applies to new processes; processes already running are
          not affected.</p>
        <p>Returns the old value of the flag.</p>
        <p>In low-memory systems (especially without virtual
          memory), setting the value to 0 can help to conserve
          memory.</p>
        <p>An alternative way to set this value is through the
          (operating system) environment variable
          <c>ERL_FULLSWEEP_AFTER</c>.</p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="5"/>
      <fsummary>Set system flag min_heap_size</fsummary>
      <desc>
        <p>Sets the default minimum heap size for processes. The
          size is given in words. The new <c>min_heap_size</c> only
          effects processes spawned after the change of
          <c>min_heap_size</c> has been made.
          The <c>min_heap_size</c> can be set for individual
          processes by use of
          <seealso marker="#spawn_opt/4">spawn_opt/N</seealso> or
          <seealso marker="#process_flag/2">process_flag/2</seealso>. </p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="6"/>
      <fsummary>Set system flag min_bin_vheap_size</fsummary>
      <desc>
        <p>Sets the default minimum binary virtual heap size for processes. The
          size is given in words. The new <c>min_bin_vhheap_size</c> only
          effects processes spawned after the change of
          <c>min_bin_vhheap_size</c> has been made.
          The <c>min_bin_vheap_size</c> can be set for individual
          processes by use of
          <seealso marker="#spawn_opt/4">spawn_opt/N</seealso> or
          <seealso marker="#process_flag/2">process_flag/2</seealso>. </p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="7"/>
      <fsummary>Set system flag multi_scheduling</fsummary>
      <desc>
        <p><marker id="system_flag_multi_scheduling"></marker>
          If multi-scheduling is enabled, more than one scheduler
          thread is used by the emulator. Multi-scheduling can be
          blocked. When multi-scheduling has been blocked, only
          one scheduler thread will schedule Erlang processes.</p>
        <p>If <c><anno>BlockState</anno> =:= block</c>, multi-scheduling will
          be blocked. If <c><anno>BlockState</anno> =:= unblock</c> and no-one
          else is blocking multi-scheduling and this process has
          only blocked one time, multi-scheduling will be unblocked.
          One process can block multi-scheduling multiple times.
          If a process has blocked multiple times, it has to
          unblock exactly as many times as it has blocked before it
          has released its multi-scheduling block. If a process that
          has blocked multi-scheduling exits, it will release its
          blocking of multi-scheduling.</p>
        <p>The return values are <c>disabled</c>, <c>blocked</c>,
          or <c>enabled</c>. The returned value describes the
          state just after the call to
          <c>erlang:system_flag(multi_scheduling, <anno>BlockState</anno>)</c>
          has been made. The return values are described in the
          documentation of <seealso marker="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</seealso>.</p>
        <p><em>NOTE</em>: Blocking of multi-scheduling should normally
          not be needed. If you feel that you need to
          block multi-scheduling, think through the
          problem at least a couple of times again.
          Blocking multi-scheduling should only be used
          as a last resort since it will most likely be
          a <em>very inefficient</em> way to solve the
          problem.</p>
        <p>See also <seealso marker="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</seealso>,
          <seealso marker="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</seealso>, and
          <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="8"/>
      <type name="scheduler_bind_type"/>
      <fsummary>Set system flag scheduler_bind_type</fsummary>
      <desc>
        <warning>
          <p><marker id="system_flag_scheduler_bind_type"></marker>
          This argument is <em>deprecated</em> and
          scheduled for removal in erts-5.10/OTP-R16. Instead of using
          this argument you are advised to use the <c>erl</c> command
          line argument <seealso marker="erts:erl#+sbt">+sbt</seealso>.
          When this argument has been removed a final scheduler bind type
          to use will be determined at emulator boot time.</p>
        </warning>
        <p>Controls if and how schedulers are bound to logical
           processors.</p>
        <p>When <c>erlang:system_flag(scheduler_bind_type, <anno>How</anno>)</c> is
           called, an asynchronous signal is sent to all schedulers
           online which causes them to try to bind or unbind as requested.
           <em>NOTE:</em> If a scheduler fails to bind, this
           will often be silently ignored. This since it isn't always
           possible to verify valid logical processor identifiers. If
           an error is reported, it will be reported to the
           <c>error_logger</c>. If you want to verify that the
           schedulers actually have bound as requested, call
           <seealso marker="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</seealso>.
        </p>
        <p>Schedulers can currently only be bound on newer Linux,
           Solaris, FreeBSD, and Windows systems, but more systems will be
           supported in the future.
        </p>
        <p>In order for the runtime system to be able to bind schedulers,
           the CPU topology needs to be known. If the runtime system fails
           to automatically detect the CPU topology, it can be defined.
           For more information on how to define the CPU topology, see
           the <c>erl</c> <seealso marker="erts:erl#+sct">+sct</seealso> command
           line flag.
        </p>
        <p>The runtime system will by default <em>not</em> bind schedulers
           to logical processors.
        </p>
        <p><em>NOTE:</em> If the Erlang runtime system is the only
           operating system process that binds threads to logical processors,
           this improves the performance of the runtime system. However,
           if other operating system processes (as for example another Erlang
           runtime system) also bind threads to logical processors, there
           might be a performance penalty instead. In some cases this
           performance penalty might be severe. If this is the case, you
           are advised to not bind the schedulers.</p>
        <p>Schedulers can be bound in different ways. The <c><anno>How</anno></c>
           argument determines how schedulers are bound. <c><anno>How</anno></c> can
           currently be one of:</p>
        <taglist>
          <tag><c>unbound</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt u</seealso>.
          </p></item>
          <tag><c>no_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt ns</seealso>.
          </p></item>
          <tag><c>thread_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt ts</seealso>.
          </p></item>
          <tag><c>processor_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt ps</seealso>.
          </p></item>
          <tag><c>spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt s</seealso>.
          </p></item>
          <tag><c>no_node_thread_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt nnts</seealso>.
          </p></item>
          <tag><c>no_node_processor_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt nnps</seealso>.
          </p></item>
          <tag><c>thread_no_node_processor_spread</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt tnnps</seealso>.
          </p></item>
          <tag><c>default_bind</c></tag>
          <item><p>Same as the <c>erl</c> command line argument
          <seealso marker="erts:erl#+sbt">+sbt db</seealso>.
          </p></item>
        </taglist>
        <p>The value returned equals <c><anno>How</anno></c> before the
           <c>scheduler_bind_type</c> flag was changed.</p>
        <p>Failure:</p>
        <taglist>
          <tag><c>notsup</c></tag>
          <item>
            <p>If binding of schedulers is not supported.</p>
          </item>
          <tag><c>badarg</c></tag>
          <item>
            <p>If <c>How</c> isn't one of the documented alternatives.</p>
          </item>
          <tag><c>badarg</c></tag>
          <item>
            <p>If no CPU topology information is available.</p>
          </item>
        </taglist>
        <p>The scheduler bind type can also be set by passing
           the <seealso marker="erts:erl#+sbt">+sbt</seealso> command
           line argument to <c>erl</c>.
        </p>
        <p>For more information, see
           <seealso marker="#system_info_scheduler_bind_type">erlang:system_info(scheduler_bind_type)</seealso>,
           <seealso marker="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</seealso>,
           the <c>erl</c> <seealso marker="erts:erl#+sbt">+sbt</seealso>
           and <seealso marker="erts:erl#+sct">+sct</seealso> command line
           flags.
        </p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="9"/>
      <fsummary>Set system flag scheduler_wall_time</fsummary>
      <desc><p><marker id="system_flag_scheduler_wall_time"></marker>
      Turns on/off scheduler wall time measurements. </p>
      <p>For more information see,
      <seealso marker="#statistics_scheduler_wall_time">erlang:statistics(scheduler_wall_time)</seealso>.
      </p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="10"/>
      <fsummary>Set system flag schedulers_online</fsummary>
      <desc>
        <p><marker id="system_flag_schedulers_online"></marker>
        Sets the amount of schedulers online. Valid range is
        <![CDATA[1 <= SchedulersOnline <= erlang:system_info(schedulers)]]>.
        </p>
        <p>Returns the old value of the flag.</p>
        <p>Note that if the emulator was built with support for <seealso
        marker="#system_flag_dirty_cpu_schedulers_online">dirty schedulers</seealso>,
        changing the number of schedulers online can also change the number of dirty
        CPU schedulers online. For example, if there are 12 schedulers and all are
        online, and 6 dirty CPU schedulers, all online as well, and <c>system_flag/2</c>
        is used to set the number of schedulers online to 6, then the number of dirty
        CPU schedulers online is automatically decreased by half as well, down to 3.
        Similarly, the number of dirty CPU schedulers online increases proportionally
        to increases in the number of schedulers online.</p>
        <p>For more information see,
        <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>,
        and
        <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>.
        </p>
      </desc>
    </func>
    <func>
      <name name="system_flag" arity="2" clause_i="11"/>
      <fsummary>Set system flag trace_control_word</fsummary>
      <desc>
        <p>Sets the value of the node's trace control word to
          <c><anno>TCW</anno></c>. <c><anno>TCW</anno></c> should be an unsigned integer. For
          more information see documentation of the
          <seealso marker="erts:match_spec#set_tcw">set_tcw</seealso>
          function in the match specification documentation in the
          ERTS User's Guide.</p>
        <p>Returns the old value of the flag.</p>
      </desc>
    </func>
    <marker id="system_flag_time_offset"/>
    <func>
      <name name="system_flag" arity="2" clause_i="12"/>
      <fsummary>Finalize the Time Offset</fsummary>
      <desc>
        <p>Finalizes the <seealso marker="#time_offset/0">time offset</seealso>
	when the <seealso marker="time_correction#Single_Time_Warp_Mode">single
	time warp mode</seealso> is being used. If another time warp mode than
	the "single time warp mode" is used, the time offset state will be left
	unchanged.</p>
        <p>Returns the old state identifier. That is, if:</p>
	<list>
	  <item><p><c>preliminary</c> is returned, finalization was
	  performed and the time offset is now final.</p></item>

	  <item><p><c>final</c> is returned, the time offset was
	  already in the final state. This either due to another
	  <c>erlang:system_flag(time_offset, finalize)</c> call, or
	  due to the
	  <seealso marker="time_correction#No_Time_Warp_Mode">no
	  time warp mode</seealso> being used.</p></item>

	  <item><p><c>volatile</c> is returned, the time offset
	  cannot be finalized due to the 
	  <seealso marker="time_correction#Multi_Time_Warp_Mode">multi
	  time warp mode</seealso> being used.</p></item>
	</list>
      </desc>
    </func>
    <func>
      <name name="system_info" arity="1" clause_i="1"/>
      <name name="system_info" arity="1" clause_i="2"/>
      <name name="system_info" arity="1" clause_i="3"/>
      <name name="system_info" arity="1" clause_i="4"/>
      <name name="system_info" arity="1" clause_i="5"/>
      <type variable="Allocator" name_i="2"/>
      <type variable="Version" name_i="2"/>
      <type variable="Features" name_i="2"/>
      <type variable="Settings" name_i="2"/>
      <type variable="Alloc" name_i="3"/>
      <fsummary>Information about the allocators of the system</fsummary>
      <desc>
        <p>
          Returns various information about the
          <marker id="system_info_allocator_tags">allocators</marker> of the
          current system (emulator) as specified by
          <c><anno>Item</anno></c>:</p>
        <taglist>
          <tag><marker id="system_info_allocated_areas"><c>allocated_areas</c></marker></tag>
          <item>
            <p>Returns a list of tuples with information about
              miscellaneous allocated memory areas.</p>
            <p>Each tuple contains an atom describing type of memory as
              first element and amount of allocated memory in bytes as
              second element. In those cases when there is information
              present about allocated and used memory, a third element
              is present. This third element contains the amount of
              used memory in bytes.</p>
            <p><c>erlang:system_info(allocated_areas)</c> is intended
              for debugging, and the content is highly implementation
              dependent. The content of the results will therefore
              change when needed without prior notice.</p>
            <p><em>Note:</em> The sum of these values is <em>not</em>
              the total amount of memory allocated by the emulator.
              Some values are part of other values, and some memory
              areas are not part of the result. If you are interested
              in the total amount of memory allocated by the emulator
              see <seealso marker="#memory/0">erlang:memory/0,1</seealso>.</p>
          </item>
          <tag><marker id="system_info_allocator"><c>allocator</c></marker></tag>
          <item>
            <p>Returns <c>{<anno>Allocator</anno>, <anno>Version</anno>, <anno>Features</anno>, <anno>Settings</anno>}.</c></p>
            <p>Explanation:</p>
            <list type="bulleted">
              <item>
                <p><c><anno>Allocator</anno></c> corresponds to the <c>malloc()</c>
                  implementation used. If <c><anno>Allocator</anno></c> equals
                  <c>undefined</c>, the <c>malloc()</c> implementation
                  used could not be identified. Currently
                  <c>glibc</c> can be identified.</p>
              </item>
              <item>
                <p><c><anno>Version</anno></c> is a list of integers (but not a
                  string) representing the version of
                  the <c>malloc()</c> implementation used.</p>
              </item>
              <item>
                <p><c><anno>Features</anno></c> is a list of atoms representing
                  allocation features used.</p>
              </item>
              <item>
                <p><c><anno>Settings</anno></c> is a list of subsystems, their
                  configurable parameters, and used values. Settings
                  may differ between different combinations of
                  platforms, allocators, and allocation features.
                  Memory sizes are given in bytes.</p>
              </item>
            </list>
            <p>See also "System Flags Effecting erts_alloc" in
              <seealso marker="erts:erts_alloc#flags">erts_alloc(3)</seealso>.</p>
          </item>
          <tag><marker id="system_info_alloc_util_allocators"><c>alloc_util_allocators</c></marker></tag>
          <item>
	     <p>Returns a list of the names of all allocators
	        using the ERTS internal <c>alloc_util</c> framework
		as atoms. For more information see the
	        <seealso marker="erts:erts_alloc#alloc_util">"the
		alloc_util framework" section in the
		erts_alloc(3)</seealso> documentation.
	     </p>
          </item>
          <tag><marker id="system_info_allocator_tuple"><c>{allocator, <anno>Alloc</anno>}</c></marker></tag>
          <item>
            <p>Returns information about the specified allocator.
	       As of erts version 5.6.1 the return value is a list
	       of <c>{instance, InstanceNo, InstanceInfo}</c> tuples
	       where <c>InstanceInfo</c> contains information about
	       a specific instance of the allocator. As of erts version
	       5.10.4 the returned list when calling
	       <c>erlang:system_info({allocator, mseg_alloc})</c> also
	       include an <c>{erts_mmap, _}</c> tuple as one element
	       in the list.
	       If <c><anno>Alloc</anno></c> is not a recognized allocator,
              <c>undefined</c> is returned. If <c><anno>Alloc</anno></c> is disabled,
              <c>false</c> is returned.</p>
            <p><em>Note:</em> The information returned is highly
              implementation dependent and may be changed, or removed
              at any time without prior notice. It was initially
              intended as a tool when developing new allocators, but
              since it might be of interest for others it has been
              briefly documented.</p>
            <p>The recognized allocators are listed in
              <seealso marker="erts:erts_alloc">erts_alloc(3)</seealso>.
              After reading the <c>erts_alloc(3)</c> documentation,
	      the returned information
              should more or less speak for itself. But it can be worth
              explaining some things. Call counts are presented by two
              values. The first value is giga calls, and the second
              value is calls. <c>mbcs</c>, and <c>sbcs</c> are
              abbreviations for, respectively, multi-block carriers, and
              single-block carriers. Sizes are presented in bytes. When
              it is not a size that is presented, it is the amount of
              something. Sizes and amounts are often presented by three
              values, the first is current value, the second is maximum
              value since the last call to
              <c>erlang:system_info({allocator, Alloc})</c>, and
              the third is maximum value since the emulator was started.
              If only one value is present, it is the current value.
              <c>fix_alloc</c> memory block types are presented by two
              values. The first value is memory pool size and
              the second value used memory size.</p>
          </item>
          <tag><marker id="system_info_allocator_sizes"><c>{allocator_sizes, <anno>Alloc</anno>}</c></marker></tag>
          <item>
	    <p>Returns various size information for the specified
	    allocator. The information returned is a subset of the
	    information returned by
	    <seealso marker="#system_info_allocator_tuple">erlang:system_info({allocator, <anno>Alloc</anno>})</seealso>.
	    </p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="system_info" arity="1" clause_i="10"/>
      <name name="system_info" arity="1" clause_i="11"/>
      <type name="cpu_topology"/>
      <type name="level_entry"/>
      <type_desc name="cpu_topology">
        <marker id="system_info_cpu_topology"></marker>
        All <c><anno>LevelEntry</anno></c>s of a list
        must contain the same <c><anno>LevelTag</anno></c>, except
        on the top level where both <c>node</c> and
        <c>processor</c> <c><anno>LevelTag</anno></c>s may co-exist.
      </type_desc>
      <type_desc name="level_entry">
       <c>{<anno>LevelTag</anno>, <anno>SubLevel</anno>} == {<anno>LevelTag</anno>, [], <anno>SubLevel</anno>}</c>
      </type_desc>
      <type name="level_tag"/>
      <type_desc name="level_tag">
        More <c><anno>LevelTag</anno></c>s may be introduced in the future.
      </type_desc>
      <type name="sub_level"/>
      <type name="info_list"/>
      <type_desc name="info_list">
        The <c>info_list()</c> may be extended in the future.
      </type_desc>
      <fsummary>Information about the CPU topology of the system</fsummary>
      <desc>
        <p>Returns various information about the
          <marker id="system_info_cpu_topology_tags">CPU topology</marker>
          of the current system
          (emulator) as specified by <c><anno>Item</anno></c>:</p>
        <taglist>
          <tag><c>cpu_topology</c></tag>
          <item>
	    <p>Returns the <c><anno>CpuTopology</anno></c> which currently is used by the
	       emulator. The CPU topology is used when binding schedulers
	       to logical processors. The CPU topology used is the
	       <seealso marker="erlang#system_info_cpu_topology_defined">user
	       defined CPU topology</seealso> if such exists; otherwise, the
	       <seealso marker="erlang#system_info_cpu_topology_detected">automatically
	       detected CPU topology</seealso> if such exists. If no CPU topology
	       exists, <c>undefined</c> is returned.</p>
	    <p><c>node</c> refers to NUMA (non-uniform memory access)
	       nodes, and <c>thread</c> refers to hardware threads
	       (e.g. Intels hyper-threads).</p>
            <p>A level in the <c><anno>CpuTopology</anno></c> term can be omitted if
	       only one entry exists and the <c><anno>InfoList</anno></c> is empty.
	    </p>
	    <p><c>thread</c> can only be a sub level to <c>core</c>.
	       <c>core</c> can be a sub level to either <c>processor</c>
	       or <c>node</c>.  <c>processor</c> can either be on the
	       top level or a sub level to <c>node</c>. <c>node</c>
	       can either be on the top level or a sub level to
	       <c>processor</c>. That is, NUMA nodes can be processor
	       internal or processor external. A CPU topology can
	       consist of a mix of processor internal and external
	       NUMA nodes, as long as each logical CPU belongs to one
	       and only one NUMA node. Cache hierarchy is not part of
	       the <c><anno>CpuTopology</anno></c> type yet, but will be in the
	       future. Other things may also make it into the CPU
	       topology in the future. In other words, expect the
	       <c><anno>CpuTopology</anno></c> type to change.
	    </p>
          </item>
          <tag><marker id="system_info_cpu_topology_defined"><c>{cpu_topology, defined}</c></marker></tag>
          <item>
            <p>Returns the user defined <c><anno>CpuTopology</anno></c>. For more
	       information see the documentation of
	       the <c>erl</c> <seealso marker="erts:erl#+sct">+sct</seealso> command
	       line flag, and the documentation of the
	       <seealso marker="#system_info_cpu_topology">cpu_topology</seealso>
	       argument.
	    </p>
          </item>
          <tag><marker id="system_info_cpu_topology_detected"><c>{cpu_topology, detected}</c></marker></tag>
          <item>
            <p>Returns the automatically detected <c><anno>CpuTopology</anno></c>. The
	       emulator currently only detects the CPU topology on some newer
	       Linux, Solaris, FreeBSD, and Windows systems. On Windows system with
	       more than 32 logical processors the CPU topology is not detected.
	    </p>
            <p>For more information see the documentation of the
	       <seealso marker="#system_info_cpu_topology">cpu_topology</seealso>
	       argument.
	    </p>
          </item>
          <tag><c>{cpu_topology, used}</c></tag>
          <item>
            <p>Returns the <c><anno>CpuTopology</anno></c> which is used by the
	       emulator. For more information see the 
               documentation of the
	       <seealso marker="#system_info_cpu_topology">cpu_topology</seealso>
	       argument.
	    </p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="system_info" arity="1" clause_i="6"/>
      <name name="system_info" arity="1" clause_i="7"/>
      <name name="system_info" arity="1" clause_i="8"/>
      <name name="system_info" arity="1" clause_i="9"/>
      <name name="system_info" arity="1" clause_i="12"/>
      <name name="system_info" arity="1" clause_i="13"/>
      <name name="system_info" arity="1" clause_i="14"/>
      <name name="system_info" arity="1" clause_i="15"/>
      <name name="system_info" arity="1" clause_i="16"/>
      <name name="system_info" arity="1" clause_i="17"/>
      <name name="system_info" arity="1" clause_i="18"/>
      <name name="system_info" arity="1" clause_i="19"/>
      <name name="system_info" arity="1" clause_i="20"/>
      <name name="system_info" arity="1" clause_i="21"/>
      <name name="system_info" arity="1" clause_i="22"/>
      <name name="system_info" arity="1" clause_i="23"/>
      <name name="system_info" arity="1" clause_i="24"/>
      <name name="system_info" arity="1" clause_i="25"/>
      <name name="system_info" arity="1" clause_i="26"/>
      <name name="system_info" arity="1" clause_i="27"/>
      <name name="system_info" arity="1" clause_i="28"/>
      <name name="system_info" arity="1" clause_i="29"/>
      <name name="system_info" arity="1" clause_i="30"/>
      <name name="system_info" arity="1" clause_i="31"/>
      <name name="system_info" arity="1" clause_i="32"/>
      <name name="system_info" arity="1" clause_i="33"/>
      <name name="system_info" arity="1" clause_i="34"/>
      <name name="system_info" arity="1" clause_i="35"/>
      <name name="system_info" arity="1" clause_i="36"/>
      <name name="system_info" arity="1" clause_i="37"/>
      <name name="system_info" arity="1" clause_i="38"/>
      <name name="system_info" arity="1" clause_i="39"/>
      <name name="system_info" arity="1" clause_i="40"/>
      <name name="system_info" arity="1" clause_i="41"/>
      <name name="system_info" arity="1" clause_i="42"/>
      <name name="system_info" arity="1" clause_i="43"/>
      <name name="system_info" arity="1" clause_i="44"/>
      <name name="system_info" arity="1" clause_i="45"/>
      <name name="system_info" arity="1" clause_i="46"/>
      <name name="system_info" arity="1" clause_i="47"/>
      <name name="system_info" arity="1" clause_i="48"/>
      <name name="system_info" arity="1" clause_i="49"/>
      <name name="system_info" arity="1" clause_i="50"/>
      <name name="system_info" arity="1" clause_i="51"/>
      <name name="system_info" arity="1" clause_i="52"/>
      <name name="system_info" arity="1" clause_i="53"/>
      <name name="system_info" arity="1" clause_i="54"/>
      <name name="system_info" arity="1" clause_i="55"/>
      <name name="system_info" arity="1" clause_i="56"/>
      <name name="system_info" arity="1" clause_i="57"/>
      <name name="system_info" arity="1" clause_i="58"/>
      <name name="system_info" arity="1" clause_i="59"/>
      <name name="system_info" arity="1" clause_i="60"/>
      <name name="system_info" arity="1" clause_i="61"/>
      <name name="system_info" arity="1" clause_i="62"/>
      <name name="system_info" arity="1" clause_i="63"/>
      <name name="system_info" arity="1" clause_i="64"/>
      <name name="system_info" arity="1" clause_i="65"/>
      <name name="system_info" arity="1" clause_i="66"/>
      <name name="system_info" arity="1" clause_i="67"/>
      <fsummary>Information about the system</fsummary>
      <desc>
        <p>Returns various information about the current system
          (emulator) as specified by <c><anno>Item</anno></c>:</p>
        <taglist>
          <tag><c>allocated_areas</c>, <c>allocator</c>,
            <c>alloc_util_allocators</c>, <c>allocator_sizes</c></tag>
          <item>
            <p>See <seealso marker="#system_info_allocator_tags">above</seealso>.</p>
          </item>
          <tag><c>build_type</c></tag>
          <item>
            <p>Returns an atom describing the build type of the runtime
	       system. This is normally the atom <c>opt</c> for optimized.
               Other possible return values are <c>debug</c>, <c>purify</c>,
	       <c>quantify</c>, <c>purecov</c>, <c>gcov</c>, <c>valgrind</c>,
	       <c>gprof</c>, and <c>lcnt</c>. Possible return values
	       may be added and/or removed at any time without prior notice.
	     </p>
          </item>
          <tag><c>c_compiler_used</c></tag>
          <item>
            <p>Returns a two-tuple describing the C compiler used when
	       compiling the runtime system. The first element is an
	       atom describing the name of the compiler, or <c>undefined</c>
	       if unknown. The second element is a term describing the
	       version of the compiler, or <c>undefined</c> if unknown.
	     </p>
          </item>
          <tag><c>check_io</c></tag>
          <item>
            <p>Returns a list containing miscellaneous information
              regarding the emulators internal I/O checking. Note,
              the content of the returned list may vary between
              platforms and over time. The only thing guaranteed is
              that a list is returned.</p>
          </item>
          <tag><c>compat_rel</c></tag>
          <item>
            <p>Returns the compatibility mode of the local node as
              an integer. The integer returned represents the
              Erlang/OTP release which the current emulator has been
              set to be backward compatible with. The compatibility
              mode can be configured at startup by using the command
              line flag <c>+R</c>, see
              <seealso marker="erts:erl#compat_rel">erl(1)</seealso>.</p>
          </item>
          <tag><c>cpu_topology</c></tag>
          <item>
            <p>See <seealso marker="#system_info_cpu_topology_tags">above</seealso>.</p>
          </item>
          <tag><c>creation</c></tag>
          <item>
            <p>Returns the creation of the local node as an integer.
              The creation is changed when a node is restarted. The
              creation of a node is stored in process identifiers, port
              identifiers, and references. This makes it (to some
              extent) possible to distinguish between identifiers from
              different incarnations of a node. Currently valid
              creations are integers in the range 1..3, but this may
              (probably will) change in the future. If the node is not
              alive, 0 is returned.</p>
          </item>
          <tag><c>debug_compiled</c></tag>
          <item>
            <p>Returns <c>true</c> if the emulator has been debug
	       compiled; otherwise, <c>false</c>.
	    </p>
          </item>
          <tag><marker id="system_info_delayed_node_table_gc"><c>delayed_node_table_gc</c></marker></tag>
          <item>
            <p>Returns the amount of time in seconds that garbage collection
	    of an entry in a node table will be delayed. This limit can be set
	    on startup by passing the
	    <seealso marker="erts:erl#+zdntgc">+zdntgc</seealso> command line
	    flag to <c>erl</c>. For more information see the documentation of the
	    command line flag.</p>
          </item>
          <tag><marker id="system_info_dirty_cpu_schedulers"><c>dirty_cpu_schedulers</c></marker></tag>
          <item>
            <p>Returns the number of dirty CPU scheduler threads used by
              the emulator. Dirty CPU schedulers execute CPU-bound
              native functions such as NIFs, linked-in driver code, and BIFs
              that cannot be managed cleanly by the emulator's normal schedulers.
            </p>
            <p>The number of dirty CPU scheduler threads is determined at emulator
              boot time and cannot be changed after that. The number of dirty CPU
              scheduler threads online can however be changed at any time. The number of
              dirty CPU schedulers can be set on startup by passing
              the <seealso marker="erts:erl#+SDcpu">+SDcpu</seealso> or
              <seealso marker="erts:erl#+SDPcpu">+SDPcpu</seealso> command line flags,
              see <seealso marker="erts:erl#+SDcpu">erl(1)</seealso>.
            </p>
	    <p><em>Note that the dirty schedulers functionality is experimental</em>, and
	    that you have to enable support for dirty schedulers when building OTP in
	    order to try out the functionality.</p>
            <p>See also <seealso marker="#system_flag_dirty_cpu_schedulers_online">erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline)</seealso>,
              <seealso marker="#system_info_dirty_cpu_schedulers_online">erlang:system_info(dirty_cpu_schedulers_online)</seealso>,
              <seealso marker="#system_info_dirty_io_schedulers">erlang:system_info(dirty_io_schedulers)</seealso>,
              <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>,
	      <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>, and
              <seealso marker="#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>.</p>
          </item>
          <tag><marker id="system_info_dirty_cpu_schedulers_online"><c>dirty_cpu_schedulers_online</c></marker></tag>
          <item>
            <p>Returns the number of dirty CPU schedulers online. The return value
              satisfies the following relationship:
              <c><![CDATA[1 <= DirtyCPUSchedulersOnline <= N]]></c>, where <c>N</c> is
              the lesser of the return values of <c>erlang:system_info(dirty_cpu_schedulers)</c> and
              <c>erlang:system_info(schedulers_online)</c>.
            </p>
            <p>The number of dirty CPU schedulers online can be set on startup by passing
              the <seealso marker="erts:erl#+SDcpu">+SDcpu</seealso> command line flag, see
              <seealso marker="erts:erl#+SDcpu">erl(1)</seealso>.
            </p>
	    <p><em>Note that the dirty schedulers functionality is experimental</em>, and
	    that you have to enable support for dirty schedulers when building OTP in
	    order to try out the functionality.</p>
            <p>For more information, see
              <seealso marker="#system_info_dirty_cpu_schedulers">erlang:system_info(dirty_cpu_schedulers)</seealso>,
              <seealso marker="#system_info_dirty_io_schedulers">erlang:system_info(dirty_io_schedulers)</seealso>,
              <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>, and
              <seealso marker="#system_flag_dirty_cpu_schedulers_online">erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline)</seealso>.
            </p>
          </item>
          <tag><marker id="system_info_dirty_io_schedulers"><c>dirty_io_schedulers</c></marker></tag>
          <item>
            <p>Returns the number of dirty I/O schedulers as an integer. Dirty I/O schedulers
              execute I/O-bound native functions such as NIFs and linked-in driver code that
              cannot be managed cleanly by the emulator's normal schedulers.
            </p>
            <p>This value can be set on startup by passing
              the <seealso marker="erts:erl#+SDio">+SDio</seealso> command line flag, see
              <seealso marker="erts:erl#+SDio">erl(1)</seealso>.
            </p>
	    <p><em>Note that the dirty schedulers functionality is experimental</em>, and
	    that you have to enable support for dirty schedulers when building OTP in
	    order to try out the functionality.</p>
            <p>For more information, see
              <seealso marker="#system_info_dirty_cpu_schedulers">erlang:system_info(dirty_cpu_schedulers)</seealso>,
              <seealso marker="#system_info_dirty_cpu_schedulers_online">erlang:system_info(dirty_cpu_schedulers_online)</seealso>, and
              <seealso marker="#system_flag_dirty_cpu_schedulers_online">erlang:system_flag(dirty_cpu_schedulers_online, DirtyCPUSchedulersOnline)</seealso>.
            </p>
          </item>
          <tag><c>dist</c></tag>
          <item>
            <p>Returns a binary containing a string of distribution
              information formatted as in Erlang crash dumps. For more
              information see the <seealso marker="erts:crash_dump">"How to interpret the Erlang crash dumps"</seealso>
              chapter in the ERTS User's Guide.</p>
          </item>
          <tag><marker id="system_info_dist_buf_busy_limit"><c>dist_buf_busy_limit</c></marker></tag>
          <item>
            <p>Returns the value of the distribution buffer busy limit
	    in bytes. This limit can be set on startup by passing the
	    <seealso marker="erts:erl#+zdbbl">+zdbbl</seealso> command line
	    flag to <c>erl</c>.</p>
          </item>
          <tag><c>dist_ctrl</c></tag>
          <item>
            <p>Returns a list of tuples
              <c>{Node, ControllingEntity}</c>, one entry for each
              connected remote node. The <c><anno>Node</anno></c> is the name of the
              node and the <c><anno>ControllingEntity</anno></c> is the port or pid
              responsible for the communication to that node. More
              specifically, the <c><anno>ControllingEntity</anno></c> for nodes
              connected via TCP/IP (the normal case) is the socket
              actually used in communication with the specific node.</p>
          </item>
          <tag><c>driver_version</c></tag>
          <item>
            <p>Returns a string containing the erlang driver version
              used by the runtime system. It will be on the form
              <seealso marker="erts:erl_driver#version_management">"&lt;major ver&gt;.&lt;minor ver&gt;"</seealso>.</p>
          </item>
          <tag><c>dynamic_trace</c></tag>
          <item>
            <p>Returns an atom describing the dynamic trace framework
            compiled into the virtual machine. It can currently be either
            <c>dtrace</c>, <c>systemtap</c> or <c>none</c>. For a
            commercial or standard build, this is always <c>none</c>,
            the other return values indicate a custom configuration
            (e.g. <c>./configure --with-dynamic-trace=dtrace</c>). See
            the <seealso marker="runtime_tools:dyntrace">dyntrace
            </seealso> manual page and the
            <c>README.dtrace</c>/<c>README.systemtap</c> files in the
            Erlang source code top directory for more information
            about dynamic tracing.</p>
          </item>
          <tag><c>dynamic_trace_probes</c></tag>
          <item>
            <p>Returns a <c>boolean()</c> indicating if dynamic trace probes
            (either dtrace or systemtap) are built into the
            emulator. This can only be <c>true</c> if the virtual
            machine was built for dynamic tracing
            (i.e. <c>system_info(dynamic_trace)</c> returns
            <c>dtrace</c> or <c>systemtap</c>).</p>
          </item>
	  <tag><marker id="system_info_end_time"/><c>end_time</c></tag>
	  <item><p>The last <seealso marker="#monotonic_time/0">Erlang monotonic
	  time</seealso> in <c>native</c>
	  <seealso marker="#type_time_unit">time unit</seealso> that
	  can be represented internally in the current Erlang runtime system
	  instance. The time between the
	  <seealso marker="#system_info_start_time">start time</seealso> and
	  the end time is at least a quarter of a millennium.</p></item>
          <tag><c>elib_malloc</c></tag>
          <item>
            <p>This option will be removed in a future release.
	      The return value will always be <c>false</c> since
	      the elib_malloc allocator has been removed.</p>
          </item>
          <tag><marker id="system_info_eager_check_io"><c>eager_check_io</c></marker></tag>
          <item>
            <p>
	      Returns the value of the <c>erl</c>
	      <seealso marker="erl#+secio">+secio</seealso> command line
	      flag which is either <c>true</c> or <c>false</c>. See the
	      documentation of the command line flag for information about
	      the different values.
	    </p>
          </item>
          <tag><c>ets_limit</c></tag>
          <item>
            <p>Returns the maximum number of ETS tables allowed. This limit
              can be increased on startup by passing the <seealso
              marker="erts:erl#+e">+e</seealso> command line flag to
              <c>erl</c> or by setting the environment variable
              <c>ERL_MAX_ETS_TABLES</c> before starting the Erlang runtime
              system.</p>
          </item>
          <tag><c>fullsweep_after</c></tag>
          <item>
            <p>Returns <c>{fullsweep_after, integer() >= 0}</c> which is the
              <c>fullsweep_after</c> garbage collection setting used
              by default. For more information see
              <c>garbage_collection</c> described below.</p>
          </item>
          <tag><c>garbage_collection</c></tag>
          <item>
            <p>Returns a list describing the default garbage collection
              settings. A process spawned on the local node by a
              <c>spawn</c> or <c>spawn_link</c> will use these
              garbage collection settings. The default settings can be
              changed by use of
              <seealso marker="#system_flag/2">system_flag/2</seealso>.
              <seealso marker="#spawn_opt/4">spawn_opt/4</seealso>
              can spawn a process that does not use the default
              settings.</p>
          </item>
          <tag><c>heap_sizes</c></tag>
          <item>
            <p>Returns a list of integers representing valid heap sizes 
              in words. All Erlang heaps are sized from sizes in this
              list.</p>
          </item>
          <tag><c>heap_type</c></tag>
          <item>
            <p>Returns the heap type used by the current emulator.
              Currently only the following heap type exists:</p>
            <taglist>
              <tag><c>private</c></tag>
              <item>
                <p>Each process has a heap reserved for its use and no
                  references between heaps of different processes are
                  allowed. Messages passed between processes are copied
                  between heaps.</p>
              </item>
            </taglist>
          </item>
          <tag><c>info</c></tag>
          <item>
            <p>Returns a binary containing a string of miscellaneous
              system information formatted as in Erlang crash dumps.
              For more information see the
              <seealso marker="erts:crash_dump">"How to interpret the Erlang crash dumps"</seealso> chapter in the ERTS
              User's Guide.</p>
          </item>
          <tag><c>kernel_poll</c></tag>
          <item>
            <p>Returns <c>true</c> if the emulator uses some kind of
              kernel-poll implementation; otherwise, <c>false</c>.</p>
          </item>
          <tag><c>loaded</c></tag>
          <item>
            <p>Returns a binary containing a string of loaded module
              information formatted as in Erlang crash dumps. For more
              information see the <seealso marker="erts:crash_dump">"How to interpret the Erlang crash dumps"</seealso> chapter
              in the ERTS User's Guide.</p>
          </item>
	  <tag><marker id="logical_processors"><c>logical_processors</c></marker></tag>
          <item>
            <p>Returns the detected number of logical processors configured
	       on the system. The return value is either an integer, or
	       the atom <c>unknown</c> if the emulator wasn't able to
	       detect logical processors configured.
	    </p>
          </item>
	  <tag><marker id="logical_processors_available"><c>logical_processors_available</c></marker></tag>
          <item>
            <p>Returns the detected number of logical processors available to
	       the Erlang runtime system. The return value is either an
	       integer, or the atom <c>unknown</c> if the emulator wasn't
	       able to detect logical processors available. The number
	       of logical processors available is less than or equal to
	       the number of <seealso marker="#logical_processors_online">logical
	       processors online</seealso>.
	    </p>
          </item>
	  <tag><marker id="logical_processors_online"><c>logical_processors_online</c></marker></tag>
          <item>
            <p>Returns the detected number of logical processors online on
	       the system. The return value is either an integer,
	       or the atom <c>unknown</c> if the emulator wasn't able to
	       detect logical processors online. The number of logical
	       processors online is less than or equal to the number of
	       <seealso marker="#logical_processors">logical processors
	       configured</seealso>.
	    </p>
          </item>
          <tag><c>machine</c></tag>
          <item>
            <p>Returns a string containing the Erlang machine name.</p>
          </item>
	  <tag><c>min_heap_size</c></tag>
          <item>
	      <p>Returns <c>{min_heap_size, <anno>MinHeapSize</anno>}</c> where <c><anno>MinHeapSize</anno></c> is the current system wide
	      minimum heap size for spawned processes.</p>
          </item>
	  <tag><c>min_bin_vheap_size</c></tag>
          <item>
	      <p>Returns <c>{min_bin_vheap_size, <anno>MinBinVHeapSize</anno>}</c> where <c><anno>MinBinVHeapSize</anno></c> is the current system wide
	      minimum binary virtual heap size for spawned processes.</p>
          </item>
          <tag><c>modified_timing_level</c></tag>
          <item>
            <p>Returns the modified timing level (an integer) if
              modified timing has been enabled; otherwise,
              <c>undefined</c>. See the <c>+T</c> command line flag
              in the documentation of the
              <seealso marker="erts:erl#+T">erl(1)</seealso>
              command for more information on modified timing.</p>
          </item>
          <tag><marker id="system_info_multi_scheduling"><c>multi_scheduling</c></marker></tag>
          <item>
            <p>Returns <c>disabled</c>, <c>blocked</c>, or <c>enabled</c>.
              A description of the return values:</p>
            <taglist>
              <tag><c>disabled</c></tag>
              <item>
                <p>The emulator has only one scheduler thread. The
                  emulator does not have SMP support, or have been
                  started with only one scheduler thread.</p>
              </item>
              <tag><c>blocked</c></tag>
              <item>
                <p>The emulator has more than one scheduler thread,
                  but all scheduler threads but one have been blocked,
                  i.e., only one scheduler thread will schedule
                  Erlang processes and execute Erlang code.</p>
              </item>
              <tag><c>enabled</c></tag>
              <item>
                <p>The emulator has more than one scheduler thread,
                  and no scheduler threads have been blocked, i.e.,
                  all available scheduler threads will schedule
                  Erlang processes and execute Erlang code.</p>
              </item>
            </taglist>
            <p>See also <seealso marker="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</seealso>,
              <seealso marker="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</seealso>, and
              <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>.</p>
          </item>
          <tag><marker id="system_info_multi_scheduling_blockers"><c>multi_scheduling_blockers</c></marker></tag>
          <item>
            <p>Returns a list of <c><anno>PID</anno></c>s when multi-scheduling
              is blocked; otherwise, the empty list. The <c><anno>PID</anno></c>s
              in the list is <c><anno>PID</anno></c>s of the processes currently
              blocking multi-scheduling. A <c><anno>PID</anno></c> will only be
              present once in the list, even if the corresponding
              process has blocked multiple times.</p>
            <p>See also <seealso marker="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</seealso>,
              <seealso marker="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</seealso>, and
              <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>.</p>
          </item>
          <tag><c>nif_version</c></tag>
          <item>
            <p>Returns a string containing the erlang NIF version
              used by the runtime system. It will be on the form "&lt;major ver&gt;.&lt;minor ver&gt;".</p>
          </item>
          <tag><marker id="system_info_otp_release"><c>otp_release</c></marker></tag>
          <item>
            <p>Returns a string containing the OTP release number of the
	    OTP release that the currently executing ERTS application is
            part of.</p>
            <p>As of OTP release 17, the OTP release number corresponds to
            the major OTP version number. There is no
	    <c>erlang:system_info()</c> argument giving the exact OTP
	    version. This since the exact OTP version in the general case
	    is hard to determine.  For more information see 
	    <seealso marker="doc/system_principles:versions">the
	    documentation of versions in the system principles
	    guide</seealso>.</p>
          </item>
          <tag><marker id="system_info_os_monotonic_time_source"><c>os_monotonic_time_source</c></marker></tag>
          <item>
            <p>Returns a list containing information about the source of
	    <seealso marker="erts:time_correction#OS_Monotonic_Time">OS
	    monotonic time</seealso> that is used by the runtime system.</p>
	    <p>In case <c>[]</c> is returned, no OS monotonic time is
	    available. The list contains two-tuples with <c>Key</c>s
	    as first element, and <c>Value</c>s as second element. The
	    order if these tuples is undefined. Currently the following
	    tuples may be part of the list, but more tuples may be
	    introduced in the future:</p>
	    <taglist>
	      <tag><c>{function, Function}</c></tag>
	      <item><p><c>Function</c> is the name of the funcion
	      used. This tuple always exist if OS monotonic time is
	      available to the runtime system.</p></item>

	      <tag><c>{clock_id, ClockId}</c></tag>
	      <item><p>This tuple only exist if <c>Function</c>
	      can be used with different clocks. <c>ClockId</c>
	      corresponds to the clock identifer used when calling
	      <c>Function</c>.</p></item>

	      <tag><c>{resolution, OsMonotonicTimeResolution}</c></tag>
	      <item><p>Highest possible
	      <seealso marker="time_correction#Time_Resolution">resolution</seealso>
	      of current OS monotonic time source as parts per
	      second. If no resolution information can be retreived
	      from the OS, <c>OsMonotonicTimeResolution</c> will be
	      set to the resolution of the time unit of
	      <c>Function</c>s return value. That is, the actual
	      resolution may be lower than
	      <c>OsMonotonicTimeResolution</c>. Also note that
	      the resolution does not say anything about the
	      <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>,
	      and that the
	      <seealso marker="time_correction#Time_Precision">precision</seealso>
	      might not align with the resolution. You do,
	      however, know that the precision won't be
	      better than
	      <c>OsMonotonicTimeResolution</c>.</p></item>

	      <tag><c>{extended, Extended}</c></tag>
	      <item><p><c>Extended</c> equals <c>yes</c> if
	      the range of time values has been extended;
	      otherwise, <c>Extended</c> equals <c>no</c>. The
	      range needs to be extended if <c>Function</c>
	      returns values that wrap fast. This typically
	      is the case when the return value is a 32-bit
	      value.</p></item>

	      <tag><c>{parallel, Parallel}</c></tag>
	      <item><p><c>Parallel</c> equals <c>yes</c> if
	      <c>Function</c> is called in parallel from multiple
	      threads. If it is not called in parallel, because
	      calls needs to be serialized, <c>Parallel</c> equals
	      <c>no</c>.</p></item>

	      <tag><c>{time, OsMonotonicTime}</c></tag>
	      <item><p><c>OsMonotonicTime</c> equals current OS
	      monotonic time in <c>native</c>
	      <seealso marker="#type_time_unit">time unit</seealso>.</p></item>
	    </taglist>
          </item>
          <tag><marker id="system_info_os_system_time_source"><c>os_system_time_source</c></marker></tag>
          <item>
            <p>Returns a list containing information about the source of
	    <seealso marker="erts:time_correction#OS_System_Time">OS
	    system time</seealso> that is used by the runtime system.</p>
	    <p>The list contains two-tuples with <c>Key</c>s
	    as first element, and <c>Value</c>s as second element. The
	    order if these tuples is undefined. Currently the following
	    tuples may be part of the list, but more tuples may be
	    introduced in the future:</p>
	    <taglist>
	      <tag><c>{function, Function}</c></tag>
	      <item><p><c>Function</c> is the name of the funcion
	      used.</p></item>

	      <tag><c>{clock_id, ClockId}</c></tag>
	      <item><p>This tuple only exist if <c>Function</c>
	      can be used with different clocks. <c>ClockId</c>
	      corresponds to the clock identifer used when calling
	      <c>Function</c>.</p></item>

	      <tag><c>{resolution, OsSystemTimeResolution}</c></tag>
	      <item><p>Highest possible
	      <seealso marker="time_correction#Time_Resolution">resolution</seealso>
	      of current OS system time source as parts per
	      second. If no resolution information can be retreived
	      from the OS, <c>OsSystemTimeResolution</c> will be
	      set to the resolution of the time unit of
	      <c>Function</c>s return value. That is, the actual
	      resolution may be lower than
	      <c>OsSystemTimeResolution</c>. Also note that
	      the resolution does not say anything about the
	      <seealso marker="time_correction#Time_Accuracy">accuracy</seealso>,
	      and that the
	      <seealso marker="time_correction#Time_Precision">precision</seealso>
	      might not align with the resolution. You do,
	      however, know that the precision won't be
	      better than
	      <c>OsSystemTimeResolution</c>.</p></item>

	      <tag><c>{parallel, Parallel}</c></tag>
	      <item><p><c>Parallel</c> equals <c>yes</c> if
	      <c>Function</c> is called in parallel from multiple
	      threads. If it is not called in parallel, because
	      calls needs to be serialized, <c>Parallel</c> equals
	      <c>no</c>.</p></item>

	      <tag><c>{time, OsSystemTime}</c></tag>
	      <item><p><c>OsSystemTime</c> equals current OS
	      system time in <c>native</c>
	      <seealso marker="#type_time_unit">time unit</seealso>.</p></item>
	    </taglist>
          </item>
	  <tag><marker id="system_info_port_parallelism"><c>port_parallelism</c></marker></tag>
	  <item><p>Returns the default port parallelism scheduling hint used.
	  For more information see the
	  <seealso marker="erl#+spp">+spp</seealso> command line argument
	  of <seealso marker="erl">erl(1)</seealso>.</p></item>
          <tag><marker id="system_info_port_count"/><c>port_count</c></tag>
          <item>
            <p>Returns the number of ports currently existing at
              the local node as an integer. The same value as
              <c>length(erlang:ports())</c> returns, but more efficient.</p>
          </item>
          <tag><marker id="system_info_port_limit"><c>port_limit</c></marker></tag>
          <item>
            <p>Returns the maximum number of simultaneously existing
              ports at the local node as an integer. This limit
              can be configured at startup by using the
              <seealso marker="erl#+Q">+Q</seealso>
	      command line flag of
	      <seealso marker="erl">erl(1)</seealso>.</p>
          </item>
          <tag><marker id="system_info_process_count"/><c>process_count</c></tag>
          <item>
            <p>Returns the number of processes currently existing at
              the local node as an integer. The same value as
              <c>length(processes())</c> returns, but more efficient.</p>
          </item>
          <tag><marker id="system_info_process_limit"><c>process_limit</c></marker></tag>
          <item>
            <p>Returns the maximum number of simultaneously existing
              processes at the local node as an integer. This limit
              can be configured at startup by using the
              <seealso marker="erl#+P">+P</seealso>
	      command line flag of
	      <seealso marker="erl">erl(1)</seealso>.</p>
          </item>
          <tag><c>procs</c></tag>
          <item>
            <p>Returns a binary containing a string of process and port
              information formatted as in Erlang crash dumps. For more
              information see the <seealso marker="erts:crash_dump">"How to interpret the Erlang crash dumps"</seealso> chapter
              in the ERTS User's Guide.</p>
          </item>
          <tag><marker id="system_info_scheduler_bind_type"><c>scheduler_bind_type</c></marker></tag>
          <item>
	    <p>Returns information on how user has requested
	       schedulers to be bound or not bound.</p>
	    <p><em>NOTE:</em> Even though user has requested
	       schedulers to be bound, they might have silently failed
	       to bind. In order to inspect actual scheduler bindings call
	       <seealso marker="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</seealso>.
	    </p>
	    <p>For more information, see
	       the <c>erl</c> <seealso marker="erts:erl#+sbt">+sbt</seealso>
	       command line argument, and
	       <seealso marker="#system_info_scheduler_bindings">erlang:system_info(scheduler_bindings)</seealso>.
	    </p>
          </item>
          <tag><marker id="system_info_scheduler_bindings"><c>scheduler_bindings</c></marker></tag>
          <item>
	    <p>Returns information on currently used scheduler
	       bindings.</p>
	    <p>A tuple of a size equal to
	       <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso> is returned. The elements of the tuple are integers
	       or the atom <c>unbound</c>. Logical processor identifiers
	       are represented as integers. The <c>N</c>th
	       element of the tuple equals the current binding for
	       the scheduler with the scheduler identifier equal to
	       <c>N</c>. E.g., if the schedulers have been bound,
	       <c>element(erlang:system_info(scheduler_id),
	       erlang:system_info(scheduler_bindings))</c> will return
	       the identifier of the logical processor that the calling
	       process is executing on.
	    </p>
	    <p>Note that only schedulers online can be bound to logical
	       processors.</p>
	    <p>For more information, see
	       the <c>erl</c> <seealso marker="erts:erl#+sbt">+sbt</seealso>
	       command line argument,
	       <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>.
	    </p>
          </item>
          <tag><marker id="system_info_scheduler_id"><c>scheduler_id</c></marker></tag>
          <item>
            <p>Returns the scheduler id (<c>SchedulerId</c>) of the
              scheduler thread that the calling process is executing
              on. <c><anno>SchedulerId</anno></c> is a positive integer; where
              <c><![CDATA[1 <= SchedulerId <= erlang:system_info(schedulers)]]></c>. See also
              <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>.</p>
          </item>
          <tag><marker id="system_info_schedulers"><c>schedulers</c></marker></tag>
          <item>
            <p>Returns the number of scheduler threads used by
              the emulator. Scheduler threads online schedules Erlang
              processes and Erlang ports, and execute Erlang code
              and Erlang linked in driver code.</p>
            <p>The number of scheduler threads is determined at
              emulator boot time and cannot be changed after
              that. The amount of schedulers online can
	      however be changed at any time.</p>
            <p>See also <seealso marker="#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>,
	      <seealso marker="#system_info_schedulers_online">erlang:system_info(schedulers_online)</seealso>,
	      <seealso marker="#system_info_scheduler_id">erlang:system_info(scheduler_id)</seealso>,
              <seealso marker="#system_flag_multi_scheduling">erlang:system_flag(multi_scheduling, BlockState)</seealso>,
              <seealso marker="#system_info_multi_scheduling">erlang:system_info(multi_scheduling)</seealso>, and
              and <seealso marker="#system_info_multi_scheduling_blockers">erlang:system_info(multi_scheduling_blockers)</seealso>.</p>
          </item>
          <tag><marker id="system_info_schedulers_online"><c>schedulers_online</c></marker></tag>
          <item>
            <p>Returns the amount of schedulers online. The scheduler
	    identifiers of schedulers online satisfy the following
	    relationship:
	    <c><![CDATA[1 <= SchedulerId <= erlang:system_info(schedulers_online)]]></c>.
	    </p>
	    <p>For more information, see
	    <seealso marker="#system_info_schedulers">erlang:system_info(schedulers)</seealso>,
	    and
	    <seealso marker="#system_flag_schedulers_online">erlang:system_flag(schedulers_online, SchedulersOnline)</seealso>.
	    </p>      <name name="system_info" arity="1" clause_i="49"/>

          </item>
          <tag><c>smp_support</c></tag>
          <item>
            <p>Returns <c>true</c> if the emulator has been compiled
              with smp support; otherwise, <c>false</c>.</p>
          </item>
	  <tag><marker id="system_info_start_time"/><c>start_time</c></tag>
	  <item><p>The <seealso marker="#monotonic_time/0">Erlang monotonic
	  time</seealso> in <c>native</c>
	  <seealso marker="#type_time_unit">time unit</seealso> at the
	  time when current Erlang runtime system instance started. See also
	  <seealso marker="#system_info_end_time"><c>erlang:system_info(end_time)</c></seealso>.
	  </p></item>
          <tag><c>system_version</c></tag>
          <item>
            <p>Returns a string containing version number and
	    some important properties such as the number of schedulers.</p>
          </item>
          <tag><c>system_architecture</c></tag>
          <item>
            <p>Returns a string containing the processor and OS
              architecture the emulator is built for.</p>
          </item>
          <tag><c>threads</c></tag>
          <item>
            <p>Returns <c>true</c> if the emulator has been compiled
              with thread support; otherwise, <c>false</c> is
              returned.</p>
          </item>
          <tag><marker id="system_info_thread_pool_size"><c>thread_pool_size</c></marker></tag>
          <item>
            <p>Returns the number of async threads in the async thread
              pool used for asynchronous driver calls
              (<seealso marker="erts:erl_driver#driver_async">driver_async()</seealso>)
              as an integer.</p>
          </item>
	  <tag><marker id="system_info_time_correction"/><c>time_correction</c></tag>
	  <item><p>Returns a boolean value indicating whether
	  <seealso marker="time_correction#Time_Correction">time correction</seealso>
	  is enabled or not.
	  </p></item>
	  <tag><marker id="system_info_time_offset"/><c>time_offset</c></tag>
	  <item><p>Returns the state of the time offset:</p>
	  <taglist>
	    <tag><c>preliminary</c></tag>
	    <item><p>The time offset is preliminary, and will be changed
	    at a later time when being finalized. The preliminary time offset
	    is used during the preliminary phase of the
	    <seealso marker="time_correction#Single_Time_Warp_Mode">single
	    time warp mode</seealso>.</p></item>

	    <tag><c>final</c></tag>
	    <item><p>The time offset is final. This
	    either due to the use of the
	    <seealso marker="time_correction#No_Time_Warp_Mode">no
	    time warp mode</seealso>, or due to the time offset having
	    been finalized when using the
	    <seealso marker="time_correction#Single_Time_Warp_Mode">single
	    time warp mode</seealso>.</p></item>

	    <tag><c>volatile</c></tag>
	    <item><p>The time offset is volatile. That is, it may
	    change at any time. This due to the
	    <seealso marker="time_correction#Multi_Time_Warp_Mode">multi
	    time warp mode</seealso> being used.</p></item>
	  </taglist>
	  </item>
	  <tag><marker id="system_info_time_warp_mode"/><c>time_warp_mode</c></tag>
	  <item><p>Returns a value identifying the
	  <seealso marker="time_correction#Time_Warp_Modes">time warp
	  mode</seealso> being used:</p>
	  <taglist>
	    <tag><c>no_time_warp</c></tag>
	    <item><p>The <seealso marker="time_correction#No_Time_Warp_Mode">no
	    time warp mode</seealso> is being used.</p></item>

	    <tag><c>single_time_warp</c></tag>
	    <item><p>The <seealso marker="time_correction#Single_Time_Warp_Mode">single
	    time warp mode</seealso> is being used.</p></item>

	    <tag><c>multi_time_warp</c></tag>
	    <item><p>The <seealso marker="time_correction#Multi_Time_Warp_Mode">multi
	    time warp mode</seealso> is being used.</p></item>
	  </taglist>
	  </item>
          <tag><marker id="system_info_tolerant_timeofday"><c>tolerant_timeofday</c></marker></tag>
          <item>
            <p>Returns whether a pre erts-7.0 backwards compatible compensation
	    for sudden changes of system time is <c>enabled</c> or <c>disabled</c>.
	    Such compensation is <c>enabled</c> when the
	    <seealso marker="#system_info_time_offset">time offset</seealso> is
	    <c>final</c>, and
	    <seealso marker="#system_info_time_correction">time correction</seealso>
	    is enabled.</p>
          </item>
          <tag><c>trace_control_word</c></tag>
          <item>
            <p>Returns the value of the node's trace control word.
              For more information see documentation of the function
              <c>get_tcw</c> in "Match Specifications in Erlang",
              <seealso marker="erts:match_spec#get_tcw">ERTS User's Guide</seealso>.</p>
          </item>
          <tag><marker id="update_cpu_info"><c>update_cpu_info</c></marker></tag>
          <item>
            <p>The runtime system rereads the CPU information available and
	       updates its internally stored information about the
	       <seealso marker="#system_info_cpu_topology_detected">detected CPU
	       topology</seealso> and the amount of logical processors
	       <seealso marker="#logical_processors">configured</seealso>,
	       <seealso marker="#logical_processors_online">online</seealso>, and
	       <seealso marker="#logical_processors_available">available</seealso>.
	       If the CPU information has changed since the last time it was read,
	       the atom <c>changed</c> is returned; otherwise, the atom
	       <c>unchanged</c> is returned. If the CPU information has changed
	       you probably want to
	       <seealso marker="#system_flag_schedulers_online">adjust the amount
	       of schedulers online</seealso>. You typically want to have as
	       many schedulers online as
	       <seealso marker="#logical_processors_available">logical processors
	       available</seealso>.
	    </p>
          </item>
          <tag><marker id="system_info_version"><c>version</c></marker></tag>
          <item>
            <p>Returns a string containing the version number of the
              emulator.</p>
          </item>
          <tag><c>wordsize</c></tag>
          <item>
            <p>Same as <c>{wordsize, internal}.</c></p>
          </item>
          <tag><c>{wordsize, internal}</c></tag>
          <item>
            <p>Returns the size of Erlang term words in bytes as an
              integer, i.e. on a 32-bit architecture 4 is returned,
              and on a pure 64-bit architecture 8 is returned. On a
              halfword 64-bit emulator, 4 is returned, as the Erlang
              terms are stored using a virtual wordsize of half the
              system's wordsize.</p>
          </item>
          <tag><c>{wordsize, external}</c></tag>
          <item>
	    <p>Returns the true wordsize of the emulator, i.e. the size
	       of a pointer, in bytes as an integer. On a pure 32-bit
	       architecture 4 is returned, on both a halfword and pure
	       64-bit architecture, 8 is returned.</p>
          </item>
        </taglist>
        <note>
          <p>The <c>scheduler</c> argument has changed name to
            <c>scheduler_id</c>. This in order to avoid mixup with
            the <c>schedulers</c> argument. The <c>scheduler</c>
            argument was introduced in ERTS version 5.5 and renamed
            in ERTS version 5.5.1.</p>
        </note>
      </desc>
    </func>

    <func>
      <name name="system_monitor" arity="0"/>
      <type name="system_monitor_option"/>
      <fsummary>Current system performance monitoring settings</fsummary>
      <desc>
        <p>Returns the current system monitoring settings set by
          <seealso marker="#system_monitor/2">erlang:system_monitor/2</seealso>
          as <c>{<anno>MonitorPid</anno>, <anno>Options</anno>}</c>, or <c>undefined</c> if there
          are no settings. The order of the options may be different
          from the one that was set.</p>
      </desc>
    </func>

    <func>
      <name name="system_monitor" arity="1"/>
      <type name="system_monitor_option"/>
      <fsummary>Set or clear system performance monitoring options</fsummary>
      <desc>
        <p>When called with the argument <c>undefined</c>, all
          system performance monitoring settings are cleared.</p>
        <p>Calling the function with <c>{<anno>MonitorPid</anno>, <anno>Options</anno>}</c> as
          argument, is the same as calling
          <seealso marker="#system_monitor/2">erlang:system_monitor(<anno>MonitorPid</anno>, <anno>Options</anno>)</seealso>.</p>
        <p>Returns the previous system monitor settings just like
          <seealso marker="#system_monitor/0">erlang:system_monitor/0</seealso>.</p>
      </desc>
    </func>

    <func>
      <name name="system_monitor" arity="2"/>
      <type name="system_monitor_option"/>
      <fsummary>Set system performance monitoring options</fsummary>
      <desc>
        <p>Sets system performance monitoring options. <c><anno>MonitorPid</anno></c>
          is a local pid that will receive system monitor messages, and
          the second argument is a list of monitoring options:</p>
        <taglist>
          <tag><c>{long_gc, Time}</c></tag>
          <item>
            <p>If a garbage collection in the system takes at least
              <c>Time</c> wallclock milliseconds, a message
              <c>{monitor, GcPid, long_gc, Info}</c> is sent to
              <c><anno>MonitorPid</anno></c>. <c>GcPid</c> is the pid that was
              garbage collected and <c>Info</c> is a list of two-element
              tuples describing the result of the garbage collection.
              One of the tuples is <c>{timeout, GcTime}</c> where
              <c>GcTime</c> is the actual time for the garbage
              collection in milliseconds. The other tuples are
              tagged with <c>heap_size</c>, <c>heap_block_size</c>,
	      <c>stack_size</c>, <c>mbuf_size</c>, <c>old_heap_size</c>,
	      and <c>old_heap_block_size</c>. These tuples are
	      explained in the documentation of the
	      <seealso marker="#gc_start">gc_start</seealso>
	      trace message (see
	      <seealso marker="#trace/3">erlang:trace/3</seealso>).
	      New tuples may be added, and the order of the tuples in
	      the <c>Info</c> list may be changed at any time without prior
	      notice.
	      </p>
          </item>
          <tag><c>{long_schedule, Time}</c></tag>
          <item>
              <p>If a process or port in the system runs uninterrupted
              for at least <c>Time</c> wall clock milliseconds, a
              message <c>{monitor, PidOrPort, long_schedule, Info}</c>
              is sent to <c>MonitorPid</c>. <c>PidOrPort</c> is the
              process or port that was running and <c>Info</c> is a
              list of two-element tuples describing the event. In case
              of a <c>pid()</c>, the tuples <c>{timeout, Millis}</c>,
              <c>{in, Location}</c> and <c>{out, Location}</c> will be
              present, where <c>Location</c> is either an MFA
              (<c>{Module, Function, Arity}</c>) describing the
              function where the process was scheduled in/out, or the
              atom <c>undefined</c>. In case of a <c>port()</c>, the
              tuples <c>{timeout, Millis}</c> and <c>{port_op,Op}</c>
              will be present. <c>Op</c> will be one of <c>proc_sig</c>,
              <c>timeout</c>, <c>input</c>, <c>output</c>,
              <c>event</c> or <c>dist_cmd</c>, depending on which
              driver callback was executing. <c>proc_sig</c> is an
              internal operation and should never appear, while the
              others represent the corresponding driver callbacks
              <c>timeout</c>, <c>ready_input</c>, <c>ready_output</c>,
              <c>event</c> and finally <c>outputv</c> (when the port
              is used by distribution).  The <c>Millis</c> value in
              the <c>timeout</c> tuple will tell you the actual
              uninterrupted execution time of the process or port,
              which will always be <c>&gt;=</c> the <c>Time</c> value
              supplied when starting the trace. New tuples may be
              added to the <c>Info</c> list in the future, and the
              order of the tuples in the list may be changed at any
              time without prior notice.
	      </p>
	      <p>This can be used to detect problems with NIF's or
	      drivers that take too long to execute. Generally, 1 ms
	      is considered a good maximum time for a driver callback
	      or a NIF. However, a time sharing system should usually
	      consider everything below 100 ms as "possible" and
	      fairly "normal". Schedule times above that might however
	      indicate swapping or a NIF/driver that is
	      misbehaving. Misbehaving NIF's and drivers could cause
	      bad resource utilization and bad overall performance of
	      the system.</p>
          </item>
          <tag><c>{large_heap, Size}</c></tag>
          <item>
            <p>If a garbage collection in the system results in
              the allocated size of a heap being at least <c>Size</c>
              words, a message <c>{monitor, GcPid, large_heap, Info}</c>
              is sent to <c><anno>MonitorPid</anno></c>. <c>GcPid</c> and <c>Info</c>
              are the same as for <c>long_gc</c> above, except that
              the tuple tagged with <c>timeout</c> is not present.
	      <em>Note</em>: As of erts version 5.6 the monitor message
	      is sent if the sum of the sizes of all memory blocks allocated
	      for all heap generations is equal to or larger than <c>Size</c>.
	      Previously the monitor message was sent if the memory block
	      allocated for the youngest generation was equal to or larger
	      than <c>Size</c>.
	    </p>
          </item>
          <tag><c>busy_port</c></tag>
          <item>
            <p>If a process in the system gets suspended because it
              sends to a busy port, a message
              <c>{monitor, SusPid, busy_port, Port}</c> is sent to
              <c><anno>MonitorPid</anno></c>. <c>SusPid</c> is the pid that got
              suspended when sending to <c>Port</c>.</p>
          </item>
          <tag><c>busy_dist_port</c></tag>
          <item>
            <p>If a process in the system gets suspended because it
              sends to a process on a remote node whose inter-node
              communication was handled by a busy port, a message
              <c>{monitor, SusPid, busy_dist_port, Port}</c> is sent to
              <c><anno>MonitorPid</anno></c>. <c>SusPid</c> is the pid that got
              suspended when sending through the inter-node
              communication port <c>Port</c>.</p>
          </item>
        </taglist>
        <p>Returns the previous system monitor settings just like
          <seealso marker="#system_monitor/0">erlang:system_monitor/0</seealso>.</p>
        <note>
          <p>If a monitoring process gets so large that it itself
            starts to cause system monitor messages when garbage
            collecting, the messages will enlarge the process's
            message queue and probably make the problem worse.</p>
          <p>Keep the monitoring process neat and do not set the system
            monitor limits too tight.</p>
        </note>
        <p>Failure: <c>badarg</c> if <c><anno>MonitorPid</anno></c> does not exist or is not a local process.</p>
      </desc>
    </func>

    <func>
      <name name="system_profile" arity="0"/>
      <type name="system_profile_option"/>
      <fsummary>Current system profiling settings</fsummary>
      <desc>
        <p>Returns the current system profiling settings set by
          <seealso marker="#system_profile/2">erlang:system_profile/2</seealso>
          as <c>{<anno>ProfilerPid</anno>, <anno>Options</anno>}</c>, or <c>undefined</c> if there
          are no settings. The order of the options may be different
          from the one that was set.</p>
      </desc>
    </func>

    <func>
      <name name="system_profile" arity="2"/>
      <type name="system_profile_option"/>
      <fsummary>Current system profiling settings</fsummary>
      <desc>
        <p>Sets system profiler options. <c><anno>ProfilerPid</anno></c>
          is a local pid or port that will receive profiling messages. The
	  receiver is excluded from all profiling.
          The second argument is a list of profiling options:</p>
        <taglist>
          <tag><c>exclusive</c></tag>
          <item>
          <p>
             If a synchronous call to a port from a process is done, the
	     calling process is considered not runnable during the call
             runtime to the port. The calling process is notified as
             <c>inactive</c> and subsequently <c>active</c> when the port
	     callback returns.
          </p>
          </item>
          <tag><c>runnable_procs</c></tag>
          <item>
          <p>If a process is put into or removed from the run queue a message, 
             <c>{profile, Pid, State, Mfa, Ts}</c>, is sent to
	     <c><anno>ProfilerPid</anno></c>. Running processes that is reinserted into the
	     run queue after having been preemptively scheduled out will not trigger this
	     message.
          </p>
          </item>
          <tag><c>runnable_ports</c></tag>
          <item>
          <p>If a port is put into or removed from the run queue a message, 
             <c>{profile, Port, State, 0, Ts}</c>, is sent to
	     <c><anno>ProfilerPid</anno></c>.
          </p>
          </item>
          <tag><c>scheduler</c></tag>
          <item>
          <p>If a scheduler is put to sleep or awoken a message,
             <c>{profile, scheduler, Id, State, NoScheds, Ts}</c>, is sent
             to <c><anno>ProfilerPid</anno></c>.
          </p>
          </item>
        </taglist>
        <note><p><c>erlang:system_profile</c> is considered experimental and
        its behaviour may change in the future.</p>
        </note>
      </desc>
    </func>
    <func>
      <name name="system_time" arity="0"/>
      <fsummary>Current Erlang system time</fsummary>
      <desc>
	<p>Returns current
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso>
	in <c>native</c>
	<seealso marker="#type_time_unit">time unit</seealso>.</p>

	<p>Calling <c>erlang:system_time()</c> is equivalent to: 
	<seealso marker="#monotonic_time/0"><c>erlang:monotonic_time()</c></seealso><c>
	+
        </c><seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso>.</p>

	<note><p>This time is <em>not</em> a monotonically increasing time
	in the general case. For more information, see the documentation of
	<seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the
	ERTS User's Guide.</p></note>
      </desc>
    </func>
    <func>
      <name name="system_time" arity="1"/>
      <fsummary>Current Erlang system time</fsummary>
      <desc>
	<p>Returns current
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso>
	converted into the <c><anno>Unit</anno></c> passed as argument.</p>

	<p>Calling <c>erlang:system_time(<anno>Unit</anno>)</c> is equivalent to: 
	<seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#system_time/0"><c>erlang:system_time()</c></seealso><c>,
	native, <anno>Unit</anno>)</c>.</p>

	<note><p>This time is <em>not</em> a monotonically increasing time
	in the general case. For more information, see the documentation of
	<seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the
	ERTS User's Guide.</p></note>
      </desc>
    </func>
    <func>
      <name name="term_to_binary" arity="1"/>
      <fsummary>Encode a term to an Erlang external term format binary</fsummary>
      <desc>
        <p>Returns a binary data object which is the result of encoding
          <c><anno>Term</anno></c> according to the Erlang external term format.</p>
        <p>This can be used for a variety of purposes, for example
          writing a term to a file in an efficient way, or sending an
          Erlang term to some type of communications channel not
          supported by distributed Erlang.</p>
        <p>See also
          <seealso marker="#binary_to_term/1">binary_to_term/1</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="term_to_binary" arity="2"/>
      <fsummary>Encode a term to en Erlang external term format binary</fsummary>
      <desc>
        <p>Returns a binary data object which is the result of encoding
          <c><anno>Term</anno></c> according to the Erlang external term format.</p>
        <p>If the option <c>compressed</c> is provided, the external
          term format will be compressed. The compressed format is
          automatically recognized by <c>binary_to_term/1</c> in R7B and later.</p>
        <p>It is also possible to specify a compression level by giving
          the option <c>{compressed, <anno>Level</anno>}</c>, where <c><anno>Level</anno></c> is an
          integer from 0 through 9. <c>0</c> means that no compression
          will be done (it is the same as not giving any <c>compressed</c> option);
          <c>1</c> will take the least time but may not compress as well as
          the higher levels; <c>9</c> will take the most time and may produce
          a smaller result. Note the "mays" in the preceding sentence; depending
          on the input term, level 9 compression may or may not produce a smaller
          result than level 1 compression.</p>
        <p>Currently, <c>compressed</c> gives the same result as
          <c>{compressed, 6}</c>.</p>
        <p>The option <c>{minor_version, <anno>Version</anno>}</c> can be use to control
          some details of the encoding. This option was
          introduced in R11B-4. Currently, the allowed values for <c><anno>Version</anno></c>
          are <c>0</c> and <c>1</c>.</p>
        <p><c>{minor_version, 1}</c> is since 17.0 the default, it forces any floats in
	  the term to be encoded
          in a more space-efficient and exact way (namely in the 64-bit IEEE format,
          rather than converted to a textual representation). <c>binary_to_term/1</c>
          in R11B-4 and later is able decode this representation.</p>
        <p><c>{minor_version, 0}</c> meaning that floats
          will be encoded using a textual representation; this option is useful if
          you want to ensure that releases prior to R11B-4 can decode resulting
          binary.</p>
        <p>See also
          <seealso marker="#binary_to_term/1">binary_to_term/1</seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="throw" arity="1"/>
      <fsummary>Throw an exception</fsummary>
      <desc>
        <p>A non-local return from a function. If evaluated within a
          <c>catch</c>, <c>catch</c> will return the value <c><anno>Any</anno></c>.</p>
        <pre>
> <input>catch throw({hello, there}).</input>
{hello,there}</pre>
        <p>Failure: <c>nocatch</c> if not evaluated within a catch.</p>
      </desc>
    </func>
    <func>
      <name name="time" arity="0"/>
      <fsummary>Current time</fsummary>
      <desc>
        <p>Returns the current time as <c>{Hour, Minute, Second}</c>.</p>
        <p>The time zone and daylight saving time correction depend on
          the underlying OS.</p>
        <pre>
> <input>time().</input>
{9,42,44}</pre>
      </desc>
    </func>
    <func>
      <name name="time_offset" arity="0"/>
      <fsummary>Current time offset</fsummary>
      <desc>
	<p>Returns the current time offset between
	<seealso marker="time_correction#Erlang_Monotonic_Time">Erlang monotonic time</seealso>
	and
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso> in
	<c>native</c> <seealso marker="#type_time_unit">time unit</seealso>.
	Current time offset added to an Erlang monotonic time gives
	corresponding Erlang system time.</p>

	<p>The time offset may or may not change during operation depending
	on the <seealso marker="time_correction#Time_Warp_Modes">time
	warp mode</seealso> used.</p>

	<note>
	  <p>A change in time offset may be observed at slightly
	  different points in time by different processes.</p>

	  <p>If the runtime system is in
	  <seealso marker="time_correction#Multi_Time_Warp_Mode">multi
	  time warp mode</seealso>, the time offset will be changed when
	  the runtime system detects that the
	  <seealso marker="time_correction#OS_System_Time">OS system
	  time</seealso> has changed. The runtime system will, however,
	  not detect this immediately when it happens. A task checking
	  the time offset is scheduled to execute at least once a minute,
	  so under normal operation this should be detected within a
	  minute, but during heavy load it might take longer time.</p>
	</note>
      </desc>
    </func>
    <func>
      <name name="time_offset" arity="1"/>
      <fsummary>Current time offset</fsummary>
      <desc>
	<p>Returns the current time offset between
	<seealso marker="time_correction#Erlang_Monotonic_Time">Erlang monotonic time</seealso>
	and
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso>
	converted into the <c><anno>Unit</anno></c> passed as argument.</p>

	<p>Same as calling	
	<seealso marker="#convert_time_unit/3"><c>erlang:convert_time_unit</c></seealso><c>(</c><seealso marker="#time_offset/0"><c>erlang:time_offset()</c></seealso><c>, native, <anno>Unit</anno>)</c>
	however optimized for commonly used <c><anno>Unit</anno></c>s.</p>
      </desc>
    </func>
    <func>
      <name name="timestamp" arity="0"/>
      <type name="timestamp"/>
      <fsummary>Current Erlang System time</fsummary>
      <desc>
	<p>Returns current
	<seealso marker="time_correction#Erlang_System_Time">Erlang system time</seealso>
	on the format <c>{MegaSecs, Secs, MicroSecs}</c>. This format is 
	the same that <seealso marker="kernel:os#timestamp/0"><c>os:timestamp/0</c></seealso>
	and the now deprecated <seealso marker="#now/0"><c>erlang:now/0</c></seealso>
	uses. The reason for the existence of <c>erlang:timestamp()</c> is
	purely to simplify usage for existing code that assumes this timestamp
	format. Current Erlang system time can more efficiently be retrieved in
	the time unit of your choice using
	<seealso marker="#system_time/1"><c>erlang:system_time/1</c></seealso>.</p>

	<p>The <c>erlang:timestamp()</c> BIF is equivalent to:</p><code type="none">
timestamp() ->
    ErlangSystemTime = erlang:system_time(micro_seconds),
    MegaSecs = ErlangSystemTime div 1000000000000,
    Secs = ErlangSystemTime div 1000000 - MegaSecs*1000000,
    MicroSecs = ErlangSystemTime rem 1000000,
    {MegaSecs, Secs, MicroSecs}.</code>
        <p>It however use a native implementation which does
	not build garbage on the heap and with slightly better
	performance.</p>

	<note><p>This time is <em>not</em> a monotonically increasing time
	in the general case. For more information, see the documentation of
	<seealso marker="time_correction#Time_Warp_Modes">time warp modes</seealso> in the
	ERTS User's Guide.</p></note>
      </desc>

    </func>
    <func>
      <name name="tl" arity="1"/>
      <fsummary>Tail of a list</fsummary>
      <desc>
        <p>Returns the tail of <c><anno>List</anno></c>, that is, the list minus
          the first element.</p>
        <pre>
> <input>tl([geesties, guilies, beasties]).</input>
[guilies, beasties]</pre>
        <p>Allowed in guard tests.</p>
        <p>Failure: <c>badarg</c> if <c><anno>List</anno></c> is the empty list [].</p>
      </desc>
    </func>
    <func>
      <name name="trace" arity="3"/>
      <type name="trace_flag"/>
      <fsummary>Set trace flags for a process or processes</fsummary>
      <desc>
        <p>Turns on (if <c><anno>How</anno> == true</c>) or off (if
          <c><anno>How</anno> == false</c>) the trace flags in <c><anno>FlagList</anno></c> for
          the process or processes represented by <c><anno>PidSpec</anno></c>.</p>
        <p><c><anno>PidSpec</anno></c> is either a pid for a local process, or one of
          the following atoms:</p>
        <taglist>
          <tag><c>existing</c></tag>
          <item>
            <p>All processes currently existing.</p>
          </item>
          <tag><c>new</c></tag>
          <item>
            <p>All processes that will be created in the future.</p>
          </item>
          <tag><c>all</c></tag>
          <item>
            <p>All currently existing processes and all processes that
              will be created in the future.</p>
          </item>
        </taglist>
        <p><c><anno>FlagList</anno></c> can contain any number of the following
          flags (the "message tags" refers to the list of messages
          following below):</p>
        <taglist>
          <tag><c>all</c></tag>
          <item>
            <p>Set all trace flags except <c>{tracer, Tracer}</c> and
              <c>cpu_timestamp</c> that are in their nature different
              than the others.</p>
          </item>
          <tag><c>send</c></tag>
          <item>
            <p>Trace sending of messages.</p>
            <p>Message tags: <c>send</c>,
              <c>send_to_non_existing_process</c>.</p>
          </item>
          <tag><c>'receive'</c></tag>
          <item>
            <p>Trace receiving of messages.</p>
            <p>Message tags: <c>'receive'</c>.</p>
          </item>
          <tag><c>procs</c></tag>
          <item>
            <p>Trace process related events.</p>
            <p>Message tags: <c>spawn</c>, <c>exit</c>,
              <c>register</c>, <c>unregister</c>, <c>link</c>,
              <c>unlink</c>, <c>getting_linked</c>,
              <c>getting_unlinked</c>.</p>
          </item>
          <tag><c>call</c></tag>
          <item>
            <p>Trace certain function calls. Specify which function
              calls to trace by calling
              <seealso marker="#trace_pattern/3">erlang:trace_pattern/3</seealso>.</p>
            <p>Message tags: <c>call</c>, <c>return_from</c>.</p>
          </item>
          <tag><c>silent</c></tag>
          <item>
            <p>Used in conjunction with the <c>call</c> trace flag.
              The <c>call</c>, <c>return_from</c> and <c>return_to</c>
              trace messages are inhibited if this flag is set,
              but if there are match specs they are executed as normal.</p>
            <p>Silent mode is inhibited by executing
              <c>erlang:trace(_, false, [silent|_])</c>,
              or by a match spec executing the <c>{silent, false}</c>
              function.</p>
            <p>The <c>silent</c> trace flag facilitates setting up
              a trace on many or even all processes in the system.
              Then the interesting trace can be activated and
              deactivated using the <c>{silent,Bool}</c>
              match spec function, giving a high degree
              of control of which functions with which 
              arguments that triggers the trace.</p>
            <p>Message tags: <c>call</c>, <c>return_from</c>, 
              <c>return_to</c>. Or rather, the absence of.</p>
          </item>
          <tag><c>return_to</c></tag>
          <item>
            <p>Used in conjunction with the <c>call</c> trace flag.
              Trace the actual return from a traced function back to
              its caller. Only works for functions traced with
              the <c>local</c> option to
              <seealso marker="#trace_pattern/3">erlang:trace_pattern/3</seealso>.</p>
            <p>The semantics is that a trace message is sent when a
              call traced function actually returns, that is, when a
              chain of tail recursive calls is ended. There will be
              only one trace message sent per chain of tail recursive
              calls, why the properties of tail recursiveness for
              function calls are kept while tracing with this flag.
              Using <c>call</c> and <c>return_to</c> trace together
              makes it possible to know exactly in which function a
              process executes at any time.</p>
            <p>To get trace messages containing return values from
              functions, use the <c>{return_trace}</c> match_spec
              action instead.</p>
            <p>Message tags: <c>return_to</c>.</p>
          </item>
          <tag><c>running</c></tag>
          <item>
            <p>Trace scheduling of processes.</p>
            <p>Message tags: <c>in</c>, and <c>out</c>.</p>
          </item>
          <tag><c>exiting</c></tag>
          <item>
            <p>Trace scheduling of an exiting processes.</p>
            <p>Message tags: <c>in_exiting</c>, <c>out_exiting</c>, and
	    <c>out_exited</c>.</p>
          </item>
          <tag><c>garbage_collection</c></tag>
          <item>
            <p>Trace garbage collections of processes.</p>
            <p>Message tags: <c>gc_start</c>, <c>gc_end</c>.</p>
          </item>
          <tag><c>timestamp</c></tag>
          <item>
            <p>Include a time stamp in all trace messages. The time
              stamp (Ts) is of the same form as returned by
              <c>erlang:now()</c>.</p>
          </item>
          <tag><c>cpu_timestamp</c></tag>
          <item>
            <p>A global trace flag for the Erlang node that makes all
              trace timestamps be in CPU time, not wallclock. It is
              only allowed with <c>PidSpec==all</c>. If the host
              machine operating system does not support high resolution
              CPU time measurements, <c>trace/3</c> exits with
              <c>badarg</c>. Note that most operating systems do
              not synchronize this value across cores, so be prepared
              that time might seem to go backwards when using this option.</p>
          </item>
          <tag><c>arity</c></tag>
          <item>
            <p>Used in conjunction with the <c>call</c> trace flag.
              <c>{M, F, Arity}</c> will be specified instead of
              <c>{M, F, Args}</c> in call trace messages.</p>
          </item>
          <tag><c>set_on_spawn</c></tag>
          <item>
            <p>Makes any process created by a traced process inherit
              its trace flags, including the <c>set_on_spawn</c> flag.</p>
          </item>
          <tag><c>set_on_first_spawn</c></tag>
          <item>
            <p>Makes the first process created by a traced process
              inherit its trace flags, excluding
              the <c>set_on_first_spawn</c> flag.</p>
          </item>
          <tag><c>set_on_link</c></tag>
          <item>
            <p>Makes any process linked by a traced process inherit its
              trace flags, including the <c>set_on_link</c> flag.</p>
          </item>
          <tag><c>set_on_first_link</c></tag>
          <item>
            <p>Makes the first process linked to by a traced process
              inherit its trace flags, excluding
              the <c>set_on_first_link</c> flag.</p>
          </item>
          <tag><c>{tracer, Tracer}</c></tag>
          <item>
            <p>Specify where to send the trace messages. <c>Tracer</c>
              must be the pid of a local process or the port identifier
              of a local port. If this flag is not given, trace
              messages will be sent to the process that called
              <c>erlang:trace/3</c>.</p>
          </item>
        </taglist>
        <p>The effect of combining <c>set_on_first_link</c> with
          <c>set_on_link</c> is the same as having
          <c>set_on_first_link</c> alone. Likewise for
          <c>set_on_spawn</c> and <c>set_on_first_spawn</c>.</p>
        <p>If the <c>timestamp</c> flag is not given, the tracing
          process will receive the trace messages described below.
          <c>Pid</c> is the pid of the traced process in which
          the traced event has occurred. The third element of the tuple
          is the message tag.</p>
        <p>If the <c>timestamp</c> flag is given, the first element of
          the tuple will be <c>trace_ts</c> instead and the timestamp
          is added last in the tuple.</p>
        <taglist>
          <tag><c>{trace, Pid, 'receive', Msg}</c></tag>
          <item>
            <p>When <c>Pid</c> receives the message <c>Msg</c>.</p>
          </item>
          <tag><c>{trace, Pid, send, Msg, To}</c></tag>
          <item>
            <p>When <c>Pid</c> sends the message <c>Msg</c> to
              the process <c>To</c>.</p>
          </item>
          <tag><c>{trace, Pid, send_to_non_existing_process, Msg, To}</c></tag>
          <item>
            <p>When <c>Pid</c> sends the message <c>Msg</c> to
              the non-existing process <c>To</c>.</p>
          </item>
          <tag><c>{trace, Pid, call, {M, F, Args}}</c></tag>
          <item>
            <p>When <c>Pid</c> calls a traced function. The return
              values of calls are never supplied, only the call and its
              arguments.</p>
            <p>Note that the trace flag <c>arity</c> can be used to
              change the contents of this message, so that <c>Arity</c>
              is specified instead of <c>Args</c>.</p>
          </item>
          <tag><c>{trace, Pid, return_to, {M, F, Arity}}</c></tag>
          <item>
            <p>When <c>Pid</c> returns <em>to</em> the specified
              function. This trace message is sent if both
              the <c>call</c> and the <c>return_to</c> flags are set,
              and the function is set to be traced on <em>local</em>
              function calls. The message is only sent when returning
              from a chain of tail recursive function calls where at
              least one call generated a <c>call</c> trace message
              (that is, the functions match specification matched and
              <c>{message, false}</c> was not an action).</p>
          </item>
          <tag><c>{trace, Pid, return_from, {M, F, Arity}, ReturnValue}</c></tag>
          <item>
            <p>When <c>Pid</c> returns <em>from</em> the specified
              function. This trace message is sent if the <c>call</c>
              flag is set, and the function has a match specification
              with a <c>return_trace</c> or <c>exception_trace</c> action.</p>
          </item>
          <tag><c>{trace, Pid, exception_from, {M, F, Arity}, {Class, Value}}</c></tag>
          <item>
            <p>When <c>Pid</c> exits <em>from</em> the specified
              function due to an exception. This trace message is sent
              if the <c>call</c> flag is set, and the function has 
              a match specification with an <c>exception_trace</c> action.</p>
          </item>
          <tag><c>{trace, Pid, spawn, Pid2, {M, F, Args}}</c></tag>
          <item>
            <p>When <c>Pid</c> spawns a new process <c>Pid2</c> with
              the specified function call as entry point.</p>
            <p>Note that <c>Args</c> is supposed to be the argument
              list, but may be any term in the case of an erroneous
              spawn.</p>
          </item>
          <tag><c>{trace, Pid, exit, Reason}</c></tag>
          <item>
            <p>When <c>Pid</c> exits with reason <c>Reason</c>.</p>
          </item>
          <tag><c>{trace, Pid, link, Pid2}</c></tag>
          <item>
            <p>When <c>Pid</c> links to a process <c>Pid2</c>.</p>
          </item>
          <tag><c>{trace, Pid, unlink, Pid2}</c></tag>
          <item>
            <p>When <c>Pid</c> removes the link from a process
              <c>Pid2</c>.</p>
          </item>
          <tag><c>{trace, Pid, getting_linked, Pid2}</c></tag>
          <item>
            <p>When <c>Pid</c> gets linked to a process <c>Pid2</c>.</p>
          </item>
          <tag><c>{trace, Pid, getting_unlinked, Pid2}</c></tag>
          <item>
            <p>When <c>Pid</c> gets unlinked from a process <c>Pid2</c>.</p>
          </item>
          <tag><c>{trace, Pid, register, RegName}</c></tag>
          <item>
            <p>When <c>Pid</c> gets the name <c>RegName</c> registered.</p>
          </item>
          <tag><c>{trace, Pid, unregister, RegName}</c></tag>
          <item>
            <p>When <c>Pid</c> gets the name <c>RegName</c> unregistered.
              Note that this is done automatically when a registered
              process exits.</p>
          </item>
          <tag><c>{trace, Pid, in, {M, F, Arity} | 0}</c></tag>
          <item>
            <p>When <c>Pid</c> is scheduled to run. The process will
              run in function <c>{M, F, Arity}</c>. On some rare
              occasions the current function cannot be determined, then
              the last element <c>Arity</c> is 0.</p>
          </item>
          <tag><c>{trace, Pid, out, {M, F, Arity} | 0}</c></tag>
          <item>
            <p>When <c>Pid</c> is scheduled out. The process was
              running in function {M, F, Arity}. On some rare occasions
              the current function cannot be determined, then the last
              element <c>Arity</c> is 0.</p>
          </item>
          <tag><marker id="gc_start"><c>{trace, Pid, gc_start, Info}</c></marker></tag>
          <item>
            <p>Sent when garbage collection is about to be started.
              <c>Info</c> is a list of two-element tuples, where
              the first element is a key, and the second is the value.
              You should not depend on the tuples have any defined
              order. Currently, the following keys are defined:</p>
            <taglist>
              <tag><c>heap_size</c></tag>
              <item>The size of the used part of the heap.</item>
	      <tag><c>heap_block_size</c></tag>
	      <item>The size of the memory block used for storing
	            the heap and the stack.</item>
              <tag><c>old_heap_size</c></tag>
              <item>The size of the used part of the old heap.</item>
	      <tag><c>old_heap_block_size</c></tag>
	      <item>The size of the memory block used for storing
	            the old heap.</item>
              <tag><c>stack_size</c></tag>
              <item>The actual size of the stack.</item>
              <tag><c>recent_size</c></tag>
              <item>The size of the data that survived the previous garbage
               collection.</item>
              <tag><c>mbuf_size</c></tag>
              <item>The combined size of message buffers associated with
               the process.</item>

              <tag><c>bin_vheap_size</c></tag>
              <item>The total size  of unique off-heap binaries referenced from the process heap.</item>
              <tag><c>bin_vheap_block_size</c></tag>
	      <item>The total size of binaries, in words, allowed in the virtual
	       heap in the process before doing a garbage collection. </item>
              <tag><c>bin_old_vheap_size</c></tag>
              <item>The total size of unique off-heap binaries referenced from the process old heap.</item>
              <tag><c>bin_vheap_block_size</c></tag>
	      <item>The total size of binaries, in words, allowed in the virtual
	       old heap in the process before doing a garbage collection. </item>


            </taglist>
            <p>All sizes are in words.</p>
          </item>
          <tag><c>{trace, Pid, gc_end, Info}</c></tag>
          <item>
            <p>Sent when garbage collection is finished. <c>Info</c>
              contains the same kind of list as in the <c>gc_start</c>
              message, but the sizes reflect the new sizes after
              garbage collection.</p>
          </item>
        </taglist>
        <p>If the tracing process dies, the flags will be silently
          removed.</p>
        <p>Only one process can trace a particular process. For this
          reason, attempts to trace an already traced process will fail.</p>
        <p>Returns: A number indicating the number of processes that
          matched <c><anno>PidSpec</anno></c>. If <c><anno>PidSpec</anno></c> is a pid,
          the return value will be <c>1</c>. If <c><anno>PidSpec</anno></c> is
          <c>all</c> or <c>existing</c> the return value will be
          the number of processes running, excluding tracer processes.
          If <c><anno>PidSpec</anno></c> is <c>new</c>, the return value will be
          <c>0</c>.</p>
        <p>Failure: If specified arguments are not supported. For
          example <c>cpu_timestamp</c> is not supported on all
          platforms.</p>
      </desc>
    </func>
    <func>
      <name name="trace_delivered" arity="1"/>
      <fsummary>Notification when trace has been delivered</fsummary>
      <desc>
        <p>The delivery of trace messages is dislocated on the time-line
          compared to other events in the system. If you know that the
          <c><anno>Tracee</anno></c> has passed some specific point in its execution,
          and you want to know when at least all trace messages
          corresponding to events up to this point have reached the tracer
          you can use <c>erlang:trace_delivered(<anno>Tracee</anno>)</c>. A
          <c>{trace_delivered, <anno>Tracee</anno>, <anno>Ref</anno>}</c> message is sent to
          the caller of <c>erlang:trace_delivered(<anno>Tracee</anno>)</c> when it
          is guaranteed that all trace messages have been delivered to
          the tracer up to the point that the <c><anno>Tracee</anno></c> had reached
          at the time of the call to
          <c>erlang:trace_delivered(<anno>Tracee</anno>)</c>.</p>
        <p>Note that the <c>trace_delivered</c> message does <em>not</em>
          imply that trace messages have been delivered; instead, it implies
          that all trace messages that <em>should</em> be delivered have
          been delivered. It is not an error if <c><anno>Tracee</anno></c> isn't, and
          hasn't been traced by someone, but if this is the case,
          <em>no</em> trace messages will have been delivered when the
          <c>trace_delivered</c> message arrives.</p>
        <p>Note that <c><anno>Tracee</anno></c> has to refer to a process currently,
          or previously existing on the same node as the caller of
          <c>erlang:trace_delivered(<anno>Tracee</anno>)</c> resides on.
          The special <c><anno>Tracee</anno></c> atom <c>all</c> denotes all processes
          that currently are traced in the node.</p>
        <p>An example: Process <c>A</c> is <c><anno>Tracee</anno></c>, port <c>B</c> is
          tracer, and process <c>C</c> is the port owner of <c>B</c>.
          <c>C</c> wants to close <c>B</c> when <c>A</c> exits. <c>C</c>
          can ensure that the trace isn't truncated by calling
          <c>erlang:trace_delivered(A)</c> when <c>A</c> exits and wait
          for the <c>{trace_delivered, A, <anno>Ref</anno>}</c> message before closing
          <c>B</c>.</p>
        <p>Failure: <c>badarg</c> if <c><anno>Tracee</anno></c> does not refer to a
          process (dead or alive) on the same node as the caller of
          <c>erlang:trace_delivered(<anno>Tracee</anno>)</c> resides on.</p>
      </desc>
    </func>
    <func>
      <name name="trace_info" arity="2"/>
      <type name="trace_info_return"/>
      <type name="trace_info_item_result"/>
      <type name="trace_info_flag"/>
      <type name="trace_match_spec"/>
      <fsummary>Trace information about a process or function</fsummary>
      <desc>
        <p>Returns trace information about a process or function.</p>
        <p>To get information about a process, <c><anno>PidOrFunc</anno></c> should
          be a pid or the atom <c>new</c>. The atom <c>new</c> means
          that the default trace state for processes to be created will
          be returned. <c><anno>Item</anno></c> must have one of the following
          values:</p>
        <taglist>
          <tag><c>flags</c></tag>
          <item>
            <p>Return a list of atoms indicating what kind of traces is
              enabled for the process. The list will be empty if no
              traces are enabled, and one or more of the followings
              atoms if traces are enabled: <c>send</c>,
              <c>'receive'</c>, <c>set_on_spawn</c>, <c>call</c>,
              <c>return_to</c>, <c>procs</c>, <c>set_on_first_spawn</c>,
              <c>set_on_link</c>, <c>running</c>,
              <c>garbage_collection</c>, <c>timestamp</c>, and
              <c>arity</c>. The order is arbitrary.</p>
          </item>
          <tag><c>tracer</c></tag>
          <item>
            <p>Return the identifier for process or port tracing this
              process. If this process is not being traced, the return
              value will be <c>[]</c>.</p>
          </item>
        </taglist>
        <p>To get information about a function, <c>PidOrFunc</c> should
          be a three-element tuple: <c>{Module, Function, Arity}</c> or
          the atom <c>on_load</c>. No wildcards are allowed. Returns
          <c>undefined</c> if the function does not exist or
          <c>false</c> if the function is not traced at all. <c>Item</c>
          must have one of the following values:</p>
        <taglist>
          <tag><c>traced</c></tag>
          <item>
            <p>Return <c>global</c> if this function is traced on
              global function calls, <c>local</c> if this function is
              traced on local function calls (i.e local and global
              function calls), and <c>false</c> if neither local nor
              global function calls are traced.</p>
          </item>
          <tag><c>match_spec</c></tag>
          <item>
            <p>Return the match specification for this function, if it
              has one. If the function is locally or globally traced but
              has no match specification defined, the returned value
              is <c>[]</c>.</p>
          </item>
          <tag><c>meta</c></tag>
          <item>
            <p>Return the meta trace tracer process or port for this
              function, if it has one. If the function is not meta
              traced the returned value is <c>false</c>, and if
              the function is meta traced but has once detected that
              the tracer proc is invalid, the returned value is [].</p>
          </item>
          <tag><c>meta_match_spec</c></tag>
          <item>
            <p>Return the meta trace match specification for this
              function, if it has one. If the function is meta traced
              but has no match specification defined, the returned
              value is <c>[]</c>.</p>
          </item>
          <tag><c>call_count</c></tag>
          <item>
            <p>Return the call count value for this function or
              <c>true</c> for the pseudo function <c>on_load</c> if call
              count tracing is active. Return <c>false</c> otherwise.
              See also
              <seealso marker="#trace_pattern/3">erlang:trace_pattern/3</seealso>.</p>
          </item>
          <tag><c>call_time</c></tag>
          <item>
	      <p>Return the call time values for this function or
              <c>true</c> for the pseudo function <c>on_load</c> if call
	      time tracing is active. Returns <c>false</c> otherwise.
	      The call time values returned, <c>[{Pid, Count, S, Us}]</c>,
	      is a list of each process that has executed the function and its specific counters.
              See also
              <seealso marker="#trace_pattern/3">erlang:trace_pattern/3</seealso>.</p>
          </item>

          <tag><c>all</c></tag>
          <item>
            <p>Return a list containing the <c>{<anno>Item</anno>, Value}</c> tuples
              for all other items, or return <c>false</c> if no tracing
              is active for this function.</p>
          </item>
        </taglist>
        <p>The actual return value will be <c>{<anno>Item</anno>, Value}</c>, where
          <c>Value</c> is the requested information as described above.
          If a pid for a dead process was given, or the name of a
          non-existing function, <c>Value</c> will be <c>undefined</c>.</p>
        <p>If <c><anno>PidOrFunc</anno></c> is the <c>on_load</c>, the information
          returned refers to the default value for code that will be
          loaded.</p>
      </desc>
    </func>
    <func>
      <name name="trace_pattern" arity="2" clause_i="1"/>
      <type name="trace_pattern_mfa"/>
      <type name="trace_match_spec"/>
      <fsummary>Set trace patterns for global call tracing</fsummary>
      <desc>
        <p>The same as
          <seealso marker="#trace_pattern/3">erlang:trace_pattern(MFA, MatchSpec, [])</seealso>,
          retained for backward compatibility.</p>
      </desc>
    </func>
    <func>
      <name name="trace_pattern" arity="3"/>
      <type name="trace_pattern_mfa"/>
      <type name="trace_match_spec"/>
      <type name="trace_pattern_flag"/>
      <fsummary>Set trace patterns for tracing of function calls</fsummary>
      <desc>
        <p>This BIF is used to enable or disable call tracing for
          exported functions. It must be combined with
          <seealso marker="#trace/3">erlang:trace/3</seealso>
          to set the <c>call</c> trace flag for one or more processes.</p>
        <p>Conceptually, call tracing works like this: Inside
          the Erlang virtual machine there is a set of processes to be
          traced and a set of functions to be traced. Tracing will be
          enabled on the intersection of the set. That is, if a process
          included in the traced process set calls a function included
          in the traced function set, the trace action will be taken.
          Otherwise, nothing will happen.</p>
        <p>Use
          <seealso marker="#trace/3">erlang:trace/3</seealso> to
          add or remove one or more processes to the set of traced
          processes. Use <c>erlang:trace_pattern/2</c> to add or remove
          exported functions to the set of traced functions.</p>
        <p>The <c>erlang:trace_pattern/3</c> BIF can also add match
          specifications to an exported function. A match specification
          comprises a pattern that the arguments to the function must
          match, a guard expression which must evaluate to <c>true</c>
          and an action to be performed. The default action is to send a
          trace message. If the pattern does not match or the guard
          fails, the action will not be executed.</p>
        <p>The <c><anno>MFA</anno></c> argument should be a tuple like
          <c>{Module, Function, Arity}</c> or the atom <c>on_load</c>
          (described below). It can be the module, function, and arity
          for an exported function (or a BIF in any module).
          The <c>'_'</c> atom can be used to mean any of that kind.
          Wildcards can be used in any of the following ways:</p>
        <taglist>
          <tag><c>{Module,Function,'_'}</c></tag>
          <item>
            <p>All exported functions of any arity named <c>Function</c>
              in module <c>Module</c>.</p>
          </item>
          <tag><c>{Module,'_','_'}</c></tag>
          <item>
            <p>All exported functions in module <c>Module</c>.</p>
          </item>
          <tag><c>{'_','_','_'}</c></tag>
          <item>
            <p>All exported functions in all loaded modules.</p>
          </item>
        </taglist>
        <p>Other combinations, such as <c>{Module,'_',Arity}</c>, are
          not allowed. Local functions will match wildcards only if
          the <c>local</c> option is in the <c><anno>FlagList</anno></c>.</p>
        <p>If the <c><anno>MFA</anno></c> argument is the atom <c>on_load</c>,
          the match specification and flag list will be used on all
          modules that are newly loaded.</p>
        <p>The <c><anno>MatchSpec</anno></c> argument can take any of the following
          forms:</p>
        <taglist>
          <tag><c>false</c></tag>
          <item>
            <p>Disable tracing for the matching function(s). Any match
              specification will be removed.</p>
          </item>
          <tag><c>true</c></tag>
          <item>
            <p>Enable tracing for the matching function(s).</p>
          </item>
          <tag><c><anno>MatchSpecList</anno></c></tag>
          <item>
            <p>A list of match specifications. An empty list is
              equivalent to <c>true</c>. See the ERTS User's Guide
              for a description of match specifications.</p>
          </item>
          <tag><c>restart</c></tag>
          <item>
	      <p>For the <c><anno>FlagList</anno></c> option <c>call_count</c> and <c>call_time</c>:
              restart the existing counters. The behaviour is undefined
              for other <c><anno>FlagList</anno></c> options.</p>
          </item>
          <tag><c>pause</c></tag>
          <item>
	      <p>For the <c><anno>FlagList</anno></c> option <c>call_count</c> and <c>call_time</c>: pause
              the existing counters. The behaviour is undefined for
              other <c>FlagList</c> options.</p>
          </item>
        </taglist>
        <p>The <c><anno>FlagList</anno></c> parameter is a list of options.
          The following options are allowed:</p>
        <taglist>
          <tag><c>global</c></tag>
          <item>
            <p>Turn on or off call tracing for global function calls
              (that is, calls specifying the module explicitly). Only
              exported functions will match and only global calls will
              generate trace messages. This is the default.</p>
          </item>
          <tag><c>local</c></tag>
          <item>
            <p>Turn on or off call tracing for all types of function
              calls. Trace messages will be sent whenever any of
              the specified functions are called, regardless of how they
              are called. If the <c>return_to</c> flag is set for
              the process, a <c>return_to</c> message will also be sent
              when this function returns to its caller.</p>
          </item>
          <tag><c>meta | {meta, <anno>Pid</anno>}</c></tag>
          <item>
            <p>Turn on or off meta tracing for all types of function
              calls. Trace messages will be sent to the tracer process
              or port <c><anno>Pid</anno></c> whenever any of the specified
              functions are called, regardless of how they are called.
              If no <c><anno>Pid</anno></c> is specified, <c>self()</c> is used as a
              default tracer process.</p>
            <p>Meta tracing traces all processes and does not care
              about the process trace flags set by <c>trace/3</c>,
              the trace flags are instead fixed to
              <c>[call, timestamp]</c>.</p>
            <p>The match spec function <c>{return_trace}</c> works with
              meta trace and send its trace message to the same tracer
              process.</p>
          </item>
          <tag><c>call_count</c></tag>
          <item>
            <p>Starts (<c><anno>MatchSpec</anno> == true</c>) or stops
              (<c><anno>MatchSpec</anno> == false</c>) call count tracing for all
              types of function calls. For every function a counter is
              incremented when the function is called, in any process.
              No process trace flags need to be activated.</p>
            <p>If call count tracing is started while already running,
              the count is restarted from zero. Running counters can be
              paused with <c><anno>MatchSpec</anno> == pause</c>. Paused and running
              counters can be restarted from zero with
              <c><anno>MatchSpec</anno> == restart</c>.</p>
            <p>The counter value can be read with
              <seealso marker="#trace_info/2">erlang:trace_info/2</seealso>.</p>
          </item>
          <tag><c>call_time</c></tag>
          <item>
            <p>Starts (<c><anno>MatchSpec</anno> == true</c>) or stops
              (<c><anno>MatchSpec</anno> == false</c>) call time tracing for all
              types of function calls. For every function a counter is
	      incremented when the function is called. Time spent in the function
	      is accumulated in two other counters, seconds and micro-seconds.
	      The counters are stored for each call traced process.</p>
            <p>If call time tracing is started while already running,
              the count and time is restarted from zero. Running counters can be
              paused with <c><anno>MatchSpec</anno> == pause</c>. Paused and running
              counters can be restarted from zero with
              <c><anno>MatchSpec</anno> == restart</c>.</p>
            <p>The counter value can be read with
              <seealso marker="#trace_info/2">erlang:trace_info/2</seealso>.</p>
          </item>

        </taglist>
        <p>The <c>global</c> and <c>local</c> options are mutually
          exclusive and <c>global</c> is the default (if no options are
          specified). The <c>call_count</c> and <c>meta</c> options
          perform a kind of local tracing, and can also not be combined
          with <c>global</c>. A function can be either globally or
          locally traced. If global tracing is specified for a
          specified set of functions; local, meta, call time and call count
          tracing for the matching set of local functions will be
          disabled, and vice versa.</p>
        <p>When disabling trace, the option must match the type of trace
          that is set on the function, so that local tracing must be
          disabled with the <c>local</c> option and global tracing with
          the <c>global</c> option (or no option at all), and so forth.</p>
        <p>There is no way to directly change part of a match
          specification list. If a function has a match specification,
          you can replace it with a completely new one. If you need to
          change an existing match specification, use the
          <seealso marker="#trace_info/2">erlang:trace_info/2</seealso>
          BIF to retrieve the existing match specification.</p>
        <p>Returns the number of exported functions that matched
          the <c><anno>MFA</anno></c> argument. This will be zero if none matched at
          all.</p>
      </desc>
    </func>
    <func>
      <name name="trunc" arity="1"/>
      <fsummary>Return an integer by the truncating a number</fsummary>
      <desc>
        <p>Returns an integer by the truncating <c><anno>Number</anno></c>.</p>
        <pre>
> <input>trunc(5.5).</input>
5</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="tuple_size" arity="1"/>
      <fsummary>Return the size of a tuple</fsummary>
      <desc>
        <p>Returns an integer which is the number of elements in <c><anno>Tuple</anno></c>.</p>
        <pre>
> <input>tuple_size({morni, mulle, bwange}).</input>
3</pre>
        <p>Allowed in guard tests.</p>
      </desc>
    </func>
    <func>
      <name name="tuple_to_list" arity="1"/>
      <fsummary>Convert a tuple to a list</fsummary>
      <desc>
        <p>Returns a list which corresponds to <c><anno>Tuple</anno></c>.
          <c><anno>Tuple</anno></c> may contain any Erlang terms.</p>
        <pre>
> <input>tuple_to_list({share, {'Ericsson_B', 163}}).</input>
[share,{'Ericsson_B',163}]</pre>
      </desc>
    </func>
    <func>
      <name name="universaltime" arity="0"/>
      <fsummary>Current date and time according to Universal Time Coordinated (UTC)</fsummary>
      <desc>
        <p>Returns the current date and time according to Universal
          Time Coordinated (UTC), also called GMT, in the form
          <c>{{Year, Month, Day}, {Hour, Minute, Second}}</c> if
          supported by the underlying operating system. If not,
          <c>erlang:universaltime()</c> is equivalent to
          <c>erlang:localtime()</c>.</p>
        <pre>
> <input>erlang:universaltime().</input>
{{1996,11,6},{14,18,43}}</pre>
      </desc>
    </func>
    <func>
      <name name="universaltime_to_localtime" arity="1"/>
      <fsummary>Convert from Universal Time Coordinated (UTC) to local date and time</fsummary>
      <desc>
        <p>Converts Universal Time Coordinated (UTC) date and time to
          local date and time, if this is supported by the underlying
          OS. Otherwise, no conversion is done, and
          <c><anno>Universaltime</anno></c> is returned.</p>
        <pre>
> <input>erlang:universaltime_to_localtime({{1996,11,6},{14,18,43}}).</input>
{{1996,11,7},{15,18,43}}</pre>
        <p>Failure: <c>badarg</c> if <c>Universaltime</c> does not denote
          a valid date and time.</p>
      </desc>
    </func>
    <func>
      <name name="unique_integer" arity="0"/>
      <fsummary>Get a unique integer value</fsummary>
      <desc>
	<p>Generates and returns an
	<seealso marker="doc/efficiency_guide:advanced#unique_integers">integer
	unique on current runtime system instance</seealso>. The same as calling
	<seealso marker="#unique_integer/1"><c>erlang:unique_integer([])</c></seealso>.</p>
      </desc>
    </func>
    <func>
      <name name="unique_integer" arity="1"/>
      <fsummary>Get a unique integer value</fsummary>
      <desc>
	<p>Generates and returns an
	<seealso marker="doc/efficiency_guide:advanced#unique_integers">integer
	unique on current runtime system
	instance</seealso>. The integer is unique in the
	sense that this BIF, using the same set of
	modifiers, will not return the same integer more
	than once on the current runtime system instance.
	Each integer value can of course be constructed
	by other means.</p>

	<p>By default, i.e. when <c>[]</c> is passed as
	<c><anno>ModifierList</anno></c>, both negative and
	positive integers will be returned. This is order
	to be able to utilize the range of integers that do
	not need to be heap allocated as much as possible.
	By default the returned integers are also only
	guaranteed to be unique, i.e., any integer returned
	may be either smaller, or larger than previously
	returned integers.</p>

	<p>Currently valid <c><anno>Modifier</anno></c>s:</p>
	<taglist>

	  <tag>positive</tag>
	  <item><p>Return only positive integers.</p>
	  <p>Note that by passing the <c>positive</c> modifier
	  you will get heap allocated integers (big-nums)
	  quicker.</p>
	  </item>

	  <tag>monotonic</tag>
	  <item><p>Return
	  <seealso marker="time_correction#Strictly_Monotonically_Increasing">strictly
	  monotonically increasing</seealso> integers
	  corresponding to creation time. That is, the integer
	  returned will always be larger than previously
	  returned integers on the current runtime system
	  instance.</p>
	  <p>These values can be used when ordering events
	  on the runtime system instance. That is, if both
	  <c>X = erlang:unique_integer([monotonic])</c> and
	  <c>Y = erlang:unique_integer([monotonic])</c> are
	  executed by different processes (or the same
	  process) on the same runtime system instance and
	  <c>X &lt; Y</c> we know that <c>X</c> was created
	  before <c>Y</c>.</p>
	  <warning><p>Strictly monotonically increasing values
	  are inherently quite expensive to generate and scales
	  poorly. This since the values needs to be
	  synchronized. That is, do not pass the <c>monotonic</c>
	  modifier unless you really need strictly monotonically
	  increasing values.</p></warning>
	  </item>

	</taglist>

	<p>All currently valid <c><anno>Modifier</anno></c>s
	can be combined. Repeated (valid)
	<c><anno>Modifier</anno></c>s in the <c>ModifierList</c>
	are ignored.</p>

	<note><p>Note that the set of integers returned by
	<c>unique_integer/1</c> using diffrent sets of
	<c><anno>Modifier</anno></c>s <em>will overlap</em>.
	For example, by calling	<c>unique_integer([monotonic])</c>,
	and <c>unique_integer([positive, monotonic])</c>
	repeatedly, you will eventually see some integers being
	returned by both calls.</p></note>

        <p>Failures:</p>
	<taglist>
	  <tag><c>badarg</c></tag>
	  <item>if <c><anno>ModifierList</anno></c> is not a
	  proper list.</item>
	  <tag><c>badarg</c></tag>
	  <item>if <c><anno>Modifier</anno></c> is not a
	  valid modifier.</item>
	</taglist>
      </desc>
    </func>
    <func>
      <name name="unlink" arity="1"/>
      <fsummary>Remove a link, if there is one, to another process or port</fsummary>
      <desc>
        <p>Removes the link, if there is one, between the calling
          process and the process or port referred to by <c><anno>Id</anno></c>.</p>
        <p>Returns <c>true</c> and does not fail, even if there is no
          link to <c><anno>Id</anno></c>, or if <c><anno>Id</anno></c> does not exist.</p>
        <p>Once <c>unlink(<anno>Id</anno>)</c> has returned it is guaranteed that
          the link between the caller and the entity referred to by
          <c><anno>Id</anno></c> has no effect on the caller in the future (unless
          the link is setup again). If caller is trapping exits, an
          <c>{'EXIT', <anno>Id</anno>, _}</c> message due to the link might have
          been placed in the caller's message queue prior to the call,
          though. Note, the <c>{'EXIT', <anno>Id</anno>, _}</c> message can be the
          result of the link, but can also be the result of <c><anno>Id</anno></c>
          calling <c>exit/2</c>. Therefore, it <em>may</em> be
          appropriate to cleanup the message queue when trapping exits
          after the call to <c>unlink(<anno>Id</anno>)</c>, as follow:</p>
        <code type="none">

    unlink(Id),
    receive
        {'EXIT', Id, _} ->
            true
    after 0 ->
            true
    end</code>
        <note>
          <p>Prior to OTP release R11B (erts version 5.5) <c>unlink/1</c>
            behaved completely asynchronous, i.e., the link was active
            until the "unlink signal" reached the linked entity. This
            had one undesirable effect, though. You could never know when
            you were guaranteed <em>not</em> to be effected by the link.</p>
          <p>Current behavior can be viewed as two combined operations:
            asynchronously send an "unlink signal" to the linked entity
            and ignore any future results of the link.</p>
        </note>
      </desc>
    </func>
    <func>
      <name name="unregister" arity="1"/>
      <fsummary>Remove the registered name for a process (or port)</fsummary>
      <desc>
        <p>Removes the registered name <c><anno>RegName</anno></c>, associated with a
          pid or a port identifier.</p>
        <pre>
> <input>unregister(db).</input>
true</pre>
        <p>Users are advised not to unregister system processes.</p>
        <p>Failure: <c>badarg</c> if <c>RegName</c> is not a registered
          name.</p>
      </desc>
    </func>
    <func>
      <name name="whereis" arity="1"/>
      <fsummary>Get the pid (or port) with a given registered name</fsummary>
      <desc>
        <p>Returns the pid or port identifier with the registered name
          <c>RegName</c>. Returns <c>undefined</c> if the name is not
          registered.</p>
        <pre>
> <input>whereis(db).</input>
&lt;0.43.0></pre>
      </desc>
    </func>
    <func>
      <name name="yield" arity="0"/>
      <fsummary>Let other processes get a chance to execute</fsummary>
      <desc>
        <p>Voluntarily let other processes (if any) get a chance to
          execute. Using <c>erlang:yield()</c> is similar to
          <c>receive after 1 -> ok end</c>, except that <c>yield()</c>
          is faster.</p>
	<warning><p>There is seldom or never any need to use this BIF,
	especially in the SMP-emulator as other	processes will have a
	chance to run in another scheduler thread anyway.
	Using this BIF without a thorough grasp of how the scheduler
	works may cause performance degradation.</p></warning>
      </desc>
    </func>
  </funcs>
</erlref>