diff options
Diffstat (limited to 'apps/couch/src/couch_work_queue.erl')
-rw-r--r-- | apps/couch/src/couch_work_queue.erl | 115 |
1 files changed, 115 insertions, 0 deletions
diff --git a/apps/couch/src/couch_work_queue.erl b/apps/couch/src/couch_work_queue.erl new file mode 100644 index 00000000..decfcad8 --- /dev/null +++ b/apps/couch/src/couch_work_queue.erl @@ -0,0 +1,115 @@ +% 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,dequeue/2,close/1]). +-export([init/1, terminate/2, handle_call/3, handle_cast/2, code_change/3, handle_info/2]). + +-record(q, { + queue=queue:new(), + 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) -> + dequeue(Wq, all). + +dequeue(Wq, MaxItems) -> + try gen_server:call(Wq, {dequeue, MaxItems}, 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={WWFrom, _}}) -> + gen_server:reply(WWFrom, 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, + queue=queue:in(Item, Q0#q.queue)}, + 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={WWFrom, _Max}}=Q) -> + gen_server:reply(WWFrom, {ok, [Item]}), + {reply, ok, Q#q{work_waiter=nil}}; +handle_call({dequeue, _Max}, _From, #q{work_waiter=WW}) when WW /= nil -> + exit("Only one caller allowed to wait for work at a time"); +handle_call({dequeue, Max}, From, #q{items=0}=Q) -> + {noreply, Q#q{work_waiter={From, Max}}}; +handle_call({dequeue, Max}, _From, #q{queue=Queue, max_size=MaxSize, + max_items=MaxItems, items=Items,close_on_dequeue=Close}=Q) -> + if Max >= Items orelse Max == all -> + [gen_server:reply(From, ok) || From <- Q#q.blocked], + Q2 = #q{max_size=MaxSize, max_items=MaxItems}, + if Close -> + {stop, normal, {ok, queue:to_list(Queue)}, Q2}; + true -> + {reply, {ok, queue:to_list(Queue)}, Q2} + end; + true -> + {DequeuedItems, Queue2, Blocked2} = + dequeue_items(Max, Queue, Q#q.blocked, []), + {reply, {ok, DequeuedItems}, + Q#q{items=Items-Max,blocked=Blocked2,queue=Queue2}} + end. + +dequeue_items(0, Queue, Blocked, DequeuedAcc) -> + {lists:reverse(DequeuedAcc), Queue, Blocked}; +dequeue_items(NumItems, Queue, Blocked, DequeuedAcc) -> + {{value, Item}, Queue2} = queue:out(Queue), + case Blocked of + [] -> + Blocked2 = Blocked; + [From|Blocked2] -> + gen_server:reply(From, ok) + end, + dequeue_items(NumItems-1, Queue2, Blocked2, [Item | DequeuedAcc]). + + +handle_cast(close, #q{items=0}=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}. |