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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 Developer of the Original Code is VMware, Inc.
%% Copyright (c) 2007-2011 VMware, Inc. All rights reserved.
%%
-module(rabbit_limiter).
-behaviour(gen_server2).
-export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2,
handle_info/2, prioritise_call/3]).
-export([start_link/2]).
-export([limit/2, can_send/3, ack/2, register/2, unregister/2]).
-export([get_limit/1, block/1, unblock/1, is_blocked/1]).
%%----------------------------------------------------------------------------
-ifdef(use_specs).
-type(maybe_pid() :: pid() | 'undefined').
-spec(start_link/2 :: (pid(), non_neg_integer()) ->
rabbit_types:ok_pid_or_error()).
-spec(limit/2 :: (maybe_pid(), non_neg_integer()) -> 'ok' | 'stopped').
-spec(can_send/3 :: (maybe_pid(), pid(), boolean()) -> boolean()).
-spec(ack/2 :: (maybe_pid(), non_neg_integer()) -> 'ok').
-spec(register/2 :: (maybe_pid(), pid()) -> 'ok').
-spec(unregister/2 :: (maybe_pid(), pid()) -> 'ok').
-spec(get_limit/1 :: (maybe_pid()) -> non_neg_integer()).
-spec(block/1 :: (maybe_pid()) -> 'ok').
-spec(unblock/1 :: (maybe_pid()) -> 'ok' | 'stopped').
-spec(is_blocked/1 :: (maybe_pid()) -> boolean()).
-endif.
%%----------------------------------------------------------------------------
-record(lim, {prefetch_count = 0,
ch_pid,
blocked = false,
queues = dict:new(), % QPid -> {MonitorRef, Notify}
volume = 0}).
%% 'Notify' is a boolean that indicates whether a queue should be
%% notified of a change in the limit or volume that may allow it to
%% deliver more messages via the limiter's channel.
%%----------------------------------------------------------------------------
%% API
%%----------------------------------------------------------------------------
start_link(ChPid, UnackedMsgCount) ->
gen_server2:start_link(?MODULE, [ChPid, UnackedMsgCount], []).
limit(undefined, 0) ->
ok;
limit(LimiterPid, PrefetchCount) ->
gen_server2:call(LimiterPid, {limit, PrefetchCount}).
%% Ask the limiter whether the queue can deliver a message without
%% breaching a limit
can_send(undefined, _QPid, _AckRequired) ->
true;
can_send(LimiterPid, QPid, AckRequired) ->
rabbit_misc:with_exit_handler(
fun () -> true end,
fun () -> gen_server2:call(LimiterPid, {can_send, QPid, AckRequired},
infinity) end).
%% Let the limiter know that the channel has received some acks from a
%% consumer
ack(undefined, _Count) -> ok;
ack(LimiterPid, Count) -> gen_server2:cast(LimiterPid, {ack, Count}).
register(undefined, _QPid) -> ok;
register(LimiterPid, QPid) -> gen_server2:cast(LimiterPid, {register, QPid}).
unregister(undefined, _QPid) -> ok;
unregister(LimiterPid, QPid) -> gen_server2:cast(LimiterPid, {unregister, QPid}).
get_limit(undefined) ->
0;
get_limit(Pid) ->
rabbit_misc:with_exit_handler(
fun () -> 0 end,
fun () -> gen_server2:call(Pid, get_limit, infinity) end).
block(undefined) ->
ok;
block(LimiterPid) ->
gen_server2:call(LimiterPid, block, infinity).
unblock(undefined) ->
ok;
unblock(LimiterPid) ->
gen_server2:call(LimiterPid, unblock, infinity).
is_blocked(undefined) ->
false;
is_blocked(LimiterPid) ->
gen_server2:call(LimiterPid, is_blocked, infinity).
%%----------------------------------------------------------------------------
%% gen_server callbacks
%%----------------------------------------------------------------------------
init([ChPid, UnackedMsgCount]) ->
{ok, #lim{ch_pid = ChPid, volume = UnackedMsgCount}}.
prioritise_call(get_limit, _From, _State) -> 9;
prioritise_call(_Msg, _From, _State) -> 0.
handle_call({can_send, _QPid, _AckRequired}, _From,
State = #lim{blocked = true}) ->
{reply, false, State};
handle_call({can_send, QPid, AckRequired}, _From,
State = #lim{volume = Volume}) ->
case limit_reached(State) of
true -> {reply, false, limit_queue(QPid, State)};
false -> {reply, true, State#lim{volume = if AckRequired -> Volume + 1;
true -> Volume
end}}
end;
handle_call(get_limit, _From, State = #lim{prefetch_count = PrefetchCount}) ->
{reply, PrefetchCount, State};
handle_call({limit, PrefetchCount}, _From, State) ->
case maybe_notify(State, State#lim{prefetch_count = PrefetchCount}) of
{cont, State1} -> {reply, ok, State1};
{stop, State1} -> {stop, normal, stopped, State1}
end;
handle_call(block, _From, State) ->
{reply, ok, State#lim{blocked = true}};
handle_call(unblock, _From, State) ->
case maybe_notify(State, State#lim{blocked = false}) of
{cont, State1} -> {reply, ok, State1};
{stop, State1} -> {stop, normal, stopped, State1}
end;
handle_call(is_blocked, _From, State) ->
{reply, blocked(State), State}.
handle_cast({ack, Count}, State = #lim{volume = Volume}) ->
NewVolume = if Volume == 0 -> 0;
true -> Volume - Count
end,
{cont, State1} = maybe_notify(State, State#lim{volume = NewVolume}),
{noreply, State1};
handle_cast({register, QPid}, State) ->
{noreply, remember_queue(QPid, State)};
handle_cast({unregister, QPid}, State) ->
{noreply, forget_queue(QPid, State)}.
handle_info({'DOWN', _MonitorRef, _Type, QPid, _Info}, State) ->
{noreply, forget_queue(QPid, State)}.
terminate(_, _) ->
ok.
code_change(_, State, _) ->
State.
%%----------------------------------------------------------------------------
%% Internal plumbing
%%----------------------------------------------------------------------------
maybe_notify(OldState, NewState) ->
case (limit_reached(OldState) orelse blocked(OldState)) andalso
not (limit_reached(NewState) orelse blocked(NewState)) of
true -> NewState1 = notify_queues(NewState),
{case NewState1#lim.prefetch_count of
0 -> stop;
_ -> cont
end, NewState1};
false -> {cont, NewState}
end.
limit_reached(#lim{prefetch_count = Limit, volume = Volume}) ->
Limit =/= 0 andalso Volume >= Limit.
blocked(#lim{blocked = Blocked}) -> Blocked.
remember_queue(QPid, State = #lim{queues = Queues}) ->
case dict:is_key(QPid, Queues) of
false -> MRef = erlang:monitor(process, QPid),
State#lim{queues = dict:store(QPid, {MRef, false}, Queues)};
true -> State
end.
forget_queue(QPid, State = #lim{ch_pid = ChPid, queues = Queues}) ->
case dict:find(QPid, Queues) of
{ok, {MRef, _}} ->
true = erlang:demonitor(MRef),
ok = rabbit_amqqueue:unblock(QPid, ChPid),
State#lim{queues = dict:erase(QPid, Queues)};
error -> State
end.
limit_queue(QPid, State = #lim{queues = Queues}) ->
UpdateFun = fun ({MRef, _}) -> {MRef, true} end,
State#lim{queues = dict:update(QPid, UpdateFun, Queues)}.
notify_queues(State = #lim{ch_pid = ChPid, queues = Queues}) ->
{QList, NewQueues} =
dict:fold(fun (_QPid, {_, false}, Acc) -> Acc;
(QPid, {MRef, true}, {L, D}) ->
{[QPid | L], dict:store(QPid, {MRef, false}, D)}
end, {[], Queues}, Queues),
case length(QList) of
0 -> ok;
L ->
%% We randomly vary the position of queues in the list,
%% thus ensuring that each queue has an equal chance of
%% being notified first.
{L1, L2} = lists:split(random:uniform(L), QList),
[ok = rabbit_amqqueue:unblock(Q, ChPid) || Q <- L2 ++ L1],
ok
end,
State#lim{queues = NewQueues}.
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