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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>sd_event_add_time</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 220</span><hr><div class="refentry"><a name="sd_event_add_time"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_event_add_time, sd_event_source_get_time, sd_event_source_set_time, sd_event_source_get_time_accuracy, sd_event_source_set_time_accuracy, sd_event_source_get_time_clock — Add a timer event source to an event loop</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-bus.h></pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_add_time</b>(</code></td><td>sd_event *<var class="pdparam">event</var>, </td></tr><tr><td> </td><td>sd_event_source **<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>clockid_t <var class="pdparam">clock</var>, </td></tr><tr><td> </td><td>uint64_t <var class="pdparam">usec</var>, </td></tr><tr><td> </td><td>uint64_t <var class="pdparam">accuracy</var>, </td></tr><tr><td> </td><td>sd_event_time_handler_t <var class="pdparam">handler</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">userdata</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">typedef int (*<b class="fsfunc">sd_event_time_handler_t</b>)(</code></td><td>sd_event_source *<var class="pdparam">s</var>, </td></tr><tr><td> </td><td>uint64_t <var class="pdparam">usec</var>, </td></tr><tr><td> </td><td>void *<var class="pdparam">userdata</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_get_time</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>usec_t *<var class="pdparam">usec</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_set_time</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>usec_t <var class="pdparam">usec</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_get_time_accuracy</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>usec_t *<var class="pdparam">usec</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_set_time_accuracy</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>usec_t <var class="pdparam">usec</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_event_source_get_time_clock</b>(</code></td><td>sd_event_source *<var class="pdparam">source</var>, </td></tr><tr><td> </td><td>clockid_t *<var class="pdparam">clock</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm140178645818976"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_event_add_time()</code> adds a new timer
event source to an event loop object. The event loop is specified
in <em class="parameter"><code>event</code></em>, the event source is returned in
the <em class="parameter"><code>source</code></em> parameter. The
<em class="parameter"><code>clock</code></em> parameter takes a clock identifier,
one of <code class="constant">CLOCK_REALTIME</code>,
<code class="constant">CLOCK_MONOTONIC</code> and
<code class="constant">CLOCK_BOOTTIME_ALARM</code>. See
<a href="http://man7.org/linux/man-pages/man2/timerfd_create.2.html"><span class="citerefentry"><span class="refentrytitle">timerfd_create</span>(2)</span></a>
for details regarding the various types of clocks. The
<em class="parameter"><code>usec</code></em> parameter takes a time value in
microseconds, relative to the clock's epoch specifying when the
timer shall elapse the earliest. The
<em class="parameter"><code>accuracy</code></em> parameter takes an additional
accuracy value in microseconds specifying a time the timer event
may be delayed. Specify 0 for selecting the default accuracy
(250ms). Specify 1 for most accurate timers. Consider specifying
60000000 or larger (1h) for long-running events that may be
delayed substantially. Picking higher accuracy values allows the
system to coalesce timer events more aggressively, thus improving
power efficiency. The <em class="parameter"><code>handler</code></em> shall
reference a function to call when the timer elapses. The handler
function will be passed the <em class="parameter"><code>userdata</code></em>
pointer, which may be chosen freely by the caller. The handler is
also passed the configured time it was triggered, however it might
actually have been called at a slightly later time, subject to the
specified accuracy value, the kernel timer slack (see
<a href="http://man7.org/linux/man-pages/man2/prctl.2.html"><span class="citerefentry"><span class="refentrytitle">prctl</span>(2)</span></a>)
and additional scheduling latencies.</p><p>By default, the timer will elapse once
(<code class="constant">SD_EVENT_ONESHOT</code>), but this may be changed
with
<a href="sd_event_source_set_enabled.html"><span class="citerefentry"><span class="refentrytitle">sd_event_source_set_enabled</span>(3)</span></a>.
If the handler function returns a negative error code, it will be
disabled after the invocation, even if
<code class="constant">SD_EVENT_ON</code> mode is set.
</p><p><code class="function">sd_event_source_get_time()</code> retrieves
the configured time value of a timer event source created
previously with <code class="function">sd_event_add_time()</code>. It takes
the event source object and a pointer to a variable to store the
time in microseconds in.</p><p><code class="function">sd_event_source_set_time()</code> changes the
configured time value of a timer event source created previously
with <code class="function">sd_event_add_time()</code>. It takes the event
source object and a time relative to the selected clock's
epoch, in microseconds.</p><p><code class="function">sd_event_source_get_time_accuracy()</code>
retrieves the configured accuracy value of a timer event source
created previously with <code class="function">sd_event_add_time()</code>. It
takes the event source object and a pointer to a variable to store
the accuracy in microseconds in.</p><p><code class="function">sd_event_source_set_time_accuracy()</code>
changes the configured accuracy of a timer event source created
previously with <code class="function">sd_event_add_time()</code>. It takes
the event source object and an accuracy, in microseconds.</p><p><code class="function">sd_event_source_get_time_clock()</code>
retrieves the configured clock of a timer event source created
previously with <code class="function">sd_event_add_time()</code>. It takes
the event source object and a pointer to a variable to store the
clock identifier in.</p></div><div class="refsect1"><a name="idm140178645798464"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p>On success, these functions return 0 or a positive
integer. On failure, they return a negative errno-style error
code. </p></div><div class="refsect1"><a name="idm140178645797168"></a><h2 id="Errors">Errors<a class="headerlink" title="Permalink to this headline" href="#Errors">¶</a></h2><p>Returned errors may indicate the following problems:</p><div class="variablelist"><dl class="variablelist"><dt id="-ENOMEM"><span class="term"><code class="constant">-ENOMEM</code></span><a class="headerlink" title="Permalink to this term" href="#-ENOMEM">¶</a></dt><dd><p>Not enough memory to allocate an object.</p></dd><dt id="-EINVAL"><span class="term"><code class="constant">-EINVAL</code></span><a class="headerlink" title="Permalink to this term" href="#-EINVAL">¶</a></dt><dd><p>An invalid argument has been passed.</p></dd><dt id="-ESTALE"><span class="term"><code class="constant">-ESTALE</code></span><a class="headerlink" title="Permalink to this term" href="#-ESTALE">¶</a></dt><dd><p>The event loop is already terminated.</p></dd><dt id="-ECHILD"><span class="term"><code class="constant">-ECHILD</code></span><a class="headerlink" title="Permalink to this term" href="#-ECHILD">¶</a></dt><dd><p>The event loop has been created in a different process.</p></dd><dt id="-EOPNOTSUPP"><span class="term"><code class="constant">-EOPNOTSUPP</code></span><a class="headerlink" title="Permalink to this term" href="#-EOPNOTSUPP">¶</a></dt><dd><p>The selected clock is not supported by the event loop implementation.</p></dd></dl></div></div><div class="refsect1"><a name="idm140178645788592"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p><code class="function">sd_event_add_time()</code> and the other functions
described here are available as a shared library, which can be
compiled and linked to with the
<code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
file.</p></div><div class="refsect1"><a name="idm140178645785408"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
<a href="sd-event.html"><span class="citerefentry"><span class="refentrytitle">sd-event</span>(3)</span></a>,
<a href="sd_event_new.html"><span class="citerefentry"><span class="refentrytitle">sd_event_new</span>(3)</span></a>,
<a href="sd_event_add_signal.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_signal</span>(3)</span></a>,
<a href="sd_event_add_child.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_child</span>(3)</span></a>,
<a href="sd_event_add_defer.html"><span class="citerefentry"><span class="refentrytitle">sd_event_add_defer</span>(3)</span></a>,
<a href="http://man7.org/linux/man-pages/man2/clock_gettime.2.html"><span class="citerefentry"><span class="refentrytitle">clock_gettime</span>(2)</span></a>,
<a href="sd_event_source_set_enabled.html"><span class="citerefentry"><span class="refentrytitle">sd_event_source_set_enabled</span>(3)</span></a>
</p></div></div></body></html>
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