keep serial in separate process, to avoid persister bottleneckbug20348

...and move all the guid functions into a separate module

1 files changed, 126 insertions, 0 deletions

diff --git a/src/rabbit_guid.erl b/src/rabbit_guid.erl
new file mode 100644
index 00000000..51c1665b
--- /dev/null
+++ b/src/rabbit_guid.erl
@@ -0,0 +1,126 @@
+%%   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}.