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%% The contents of this file are subject to the Mozilla Public License
%% Version 1.1 (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.mozilla.org/MPL/
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
%% License for the specific language governing rights and limitations
%% under the License.
%%
%% The Original Code is RabbitMQ.
%%
%% The Initial Developers of the Original Code are LShift Ltd,
%% Cohesive Financial Technologies LLC, and Rabbit Technologies Ltd.
%%
%% Portions created before 22-Nov-2008 00:00:00 GMT by LShift Ltd,
%% Cohesive Financial Technologies LLC, or Rabbit Technologies Ltd
%% are Copyright (C) 2007-2008 LShift Ltd, Cohesive Financial
%% Technologies LLC, and Rabbit Technologies Ltd.
%%
%% Portions created by LShift Ltd are Copyright (C) 2007-2009 LShift
%% Ltd. Portions created by Cohesive Financial Technologies LLC are
%% Copyright (C) 2007-2009 Cohesive Financial Technologies
%% LLC. Portions created by Rabbit Technologies Ltd are Copyright
%% (C) 2007-2009 Rabbit Technologies Ltd.
%%
%% All Rights Reserved.
%%
%% Contributor(s): ______________________________________.
%%
-module(rabbit_guid).
-include("rabbit.hrl").
-behaviour(gen_server).
-export([start_link/0]).
-export([guid/0, string_guid/1, binstring_guid/1]).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
-record(state, {serial}).
%%----------------------------------------------------------------------------
-ifdef(use_specs).
-spec(start_link/0 :: () -> {'ok', pid()} | 'ignore' | {'error', any()}).
-spec(guid/0 :: () -> guid()).
-spec(string_guid/1 :: (any()) -> string()).
-spec(binstring_guid/1 :: (any()) -> binary()).
-endif.
%%----------------------------------------------------------------------------
start_link() ->
%% The persister can get heavily loaded, and we don't want that to
%% impact guid generation. We therefore keep the serial in a
%% separate process rather than calling rabbit_persister:serial/0
%% directly in the functions below.
gen_server:start_link({local, ?SERVER}, ?MODULE,
[rabbit_persister:serial()], []).
%% generate a guid that is monotonically increasing per process.
%%
%% The id is only unique within a single cluster and as long as the
%% persistent message store hasn't been deleted.
guid() ->
%% We don't use erlang:now() here because a) it may return
%% duplicates when the system clock has been rewound prior to a
%% restart, or ids were generated at a high rate (which causes
%% now() to move ahead of the system time), and b) it is really
%% slow since it takes a global lock and makes a system call.
%%
%% rabbit_persister:serial/0, in combination with self/0 (which
%% includes the node name) uniquely identifies a process in space
%% and time. We combine that with a process-local counter to give
%% us a GUID that is monotonically increasing per process.
G = case get(guid) of
undefined -> {{gen_server:call(?SERVER, serial), self()}, 0};
{S, I} -> {S, I+1}
end,
put(guid, G),
G.
%% generate a readable string representation of a guid. Note that any
%% monotonicity of the guid is not preserved in the encoding.
string_guid(Prefix) ->
%% we use the (undocumented) ssl_base64 module here because it is
%% present throughout OTP R11 and R12 whereas base64 only becomes
%% available in R11B-4.
%%
%% TODO: once debian stable and EPEL have moved from R11B-2 to
%% R11B-4 or later we should change this to use base64.
Prefix ++ "-" ++ ssl_base64:encode(erlang:md5(term_to_binary(guid()))).
binstring_guid(Prefix) ->
list_to_binary(string_guid(Prefix)).
%%----------------------------------------------------------------------------
init([Serial]) ->
{ok, #state{serial = Serial}}.
handle_call(serial, _From, State = #state{serial = Serial}) ->
{reply, Serial, State};
handle_call(_Request, _From, State) ->
{noreply, State}.
handle_cast(_Msg, State) ->
{noreply, State}.
handle_info(_Info, State) ->
{noreply, State}.
terminate(_Reason, _State) ->
ok.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
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