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% 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.
-module(couch_work_queue).
-behaviour(gen_server).
-export([new/2,queue/2,dequeue/1,close/1]).
-export([init/1, terminate/2, handle_call/3, handle_cast/2, code_change/3, handle_info/2]).
-record(q, {
buffer=[],
blocked=[],
max_size,
max_items,
items=0,
size=0,
work_waiter=nil,
close_on_dequeue=false
}).
new(MaxSize, MaxItems) ->
gen_server:start_link(couch_work_queue, {MaxSize, MaxItems}, []).
queue(Wq, Item) ->
gen_server:call(Wq, {queue, Item}, infinity).
dequeue(Wq) ->
try gen_server:call(Wq, dequeue, infinity)
catch
_:_ -> closed
end.
close(Wq) ->
gen_server:cast(Wq, close).
init({MaxSize,MaxItems}) ->
{ok, #q{max_size=MaxSize, max_items=MaxItems}}.
terminate(_Reason, #q{work_waiter=nil}) ->
ok;
terminate(_Reason, #q{work_waiter=WW}) ->
gen_server:reply(WW, closed).
handle_call({queue, Item}, From, #q{work_waiter=nil}=Q0) ->
Q = Q0#q{size=Q0#q.size + byte_size(term_to_binary(Item)),
items=Q0#q.items + 1,
buffer=[Item | Q0#q.buffer]},
case (Q#q.size >= Q#q.max_size) orelse
(Q#q.items >= Q#q.max_items) of
true ->
{noreply, Q#q{blocked=[From | Q#q.blocked]}};
false ->
{reply, ok, Q}
end;
handle_call({queue, Item}, _From, #q{work_waiter=WW}=Q) ->
gen_server:reply(WW, {ok, [Item]}),
{reply, ok, Q#q{work_waiter=nil}};
handle_call(dequeue, _From, #q{work_waiter=WW}) when WW /= nil ->
exit("Only one caller allowed to wait for work at a time");
handle_call(dequeue, From, #q{items=0}=Q) ->
{noreply, Q#q{work_waiter=From}};
handle_call(dequeue, _From, #q{buffer=Buff, max_size=MaxSize,
max_items=MaxItems, close_on_dequeue=Close}=Q) ->
[gen_server:reply(From, ok) || From <- Q#q.blocked],
Q2 = #q{max_size=MaxSize, max_items=MaxItems},
if Close ->
{stop, normal, {ok, Buff}, Q2};
true ->
{reply, {ok, Buff}, #q{max_size=MaxSize, max_items=MaxItems}}
end.
handle_cast(close, #q{buffer=[]}=Q) ->
{stop, normal, Q};
handle_cast(close, Q) ->
{noreply, Q#q{close_on_dequeue=true}}.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_info(X, Q) ->
{stop, X, Q}.
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