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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_ref_counter).
-behaviour(gen_server).
-export([start/1, init/1, terminate/2, handle_call/3, handle_cast/2, code_change/3, handle_info/2]).
-export([drop/1,drop/2,add/1,add/2,count/1]).
start(ChildProcs) ->
gen_server:start(couch_ref_counter, {self(), ChildProcs}, []).
drop(RefCounterPid) ->
drop(RefCounterPid, self()).
drop(RefCounterPid, Pid) ->
gen_server:cast(RefCounterPid, {drop, Pid}).
add(RefCounterPid) ->
add(RefCounterPid, self()).
add(RefCounterPid, Pid) ->
gen_server:call(RefCounterPid, {add, Pid}).
count(RefCounterPid) ->
gen_server:call(RefCounterPid, count).
% server functions
-record(srv,
{
referrers=dict:new() % a dict of each ref counting proc.
}).
init({Pid, ChildProcs}) ->
[link(ChildProc) || ChildProc <- ChildProcs],
Referrers = dict:from_list([{Pid, {erlang:monitor(process, Pid), 1}}]),
{ok, #srv{referrers=Referrers}}.
terminate(Reason, _Srv) ->
couch_util:terminate_linked(Reason),
ok.
handle_call({add, Pid},_From, #srv{referrers=Referrers}=Srv) ->
Referrers2 =
case dict:find(Pid, Referrers) of
error ->
dict:store(Pid, {erlang:monitor(process, Pid), 1}, Referrers);
{ok, {MonRef, RefCnt}} ->
dict:store(Pid, {MonRef, RefCnt + 1}, Referrers)
end,
{reply, ok, Srv#srv{referrers=Referrers2}};
handle_call(count, _From, Srv) ->
{monitors, Monitors} = process_info(self(), monitors),
{reply, length(Monitors), Srv}.
handle_cast({drop, Pid}, #srv{referrers=Referrers}=Srv) ->
Referrers2 =
case dict:find(Pid, Referrers) of
{ok, {MonRef, 1}} ->
erlang:demonitor(MonRef, [flush]),
dict:erase(Pid, Referrers);
{ok, {MonRef, Num}} ->
dict:store(Pid, {MonRef, Num-1}, Referrers);
error ->
Referrers
end,
maybe_close_async(Srv#srv{referrers=Referrers2}).
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
handle_info({'DOWN', MonRef, _, Pid, _}, #srv{referrers=Referrers}=Srv) ->
{ok, {MonRef, _RefCount}} = dict:find(Pid, Referrers),
maybe_close_async(Srv#srv{referrers=dict:erase(Pid, Referrers)}).
should_close() ->
case process_info(self(), monitors) of
{monitors, []} ->
true;
_ ->
false
end.
maybe_close_async(Srv) ->
case should_close() of
true ->
{stop,normal,Srv};
false ->
{noreply,Srv}
end.
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