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%% ``The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved via the world wide web at http://www.erlang.org/.
%%
%% 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 Initial Developer of the Original Code is Ericsson Utvecklings AB.
%% Portions created by Ericsson are Copyright 1999, Ericsson Utvecklings
%% AB. All Rights Reserved.''
%%
%% @author Ulf Wiger <ulf.wiger@feuerlabs.com>
%%
%% @doc
%% This module implements a notification system for gproc names
%% When a process subscribes to notifications for a given name, a message
%% will be sent each time that name is registered
-module(gproc_monitor).
-behaviour(gen_server).
%% API
-export([subscribe/1,
unsubscribe/1]).
%% Process start function
-export([start_link/0]).
%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
terminate/2, code_change/3]).
-define(SERVER, ?MODULE).
-define(TAB, ?MODULE).
-record(state, {}).
%%%===================================================================
%%% API
%%%===================================================================
%%--------------------------------------------------------------------
%% @spec subscribe(key()) -> ok
%%
%% @doc
%% Subscribe to registration events for a certain name
%%
%% The subscribing process will receive a `{gproc_monitor, Name, Pid}' message
%% whenever a process registers under the given name, and a
%% `{gproc_monitor, Name, undefined}' message when the name is unregistered,
%% either explicitly, or because the registered process dies.
%%
%% When the subscription is first ordered, one of the above messages will be
%% sent immediately, indicating the current status of the name.
%% @end
%%--------------------------------------------------------------------
subscribe({T,S,_} = Key) when (T==n orelse T==a)
andalso (S==g orelse S==l) ->
try gproc:reg({p,l,{?MODULE,Key}})
catch
error:badarg -> ok
end,
gen_server:cast(?SERVER, {subscribe, self(), Key}).
%%--------------------------------------------------------------------
%% @spec unsubscribe(key()) -> ok
%%
%% @doc
%% Unsubscribe from registration events for a certain name
%%
%% This function is the reverse of subscribe/1. It removes the subscription.
%% @end
%%--------------------------------------------------------------------
unsubscribe({T,S,_} = Key) when (T==n orelse T==a)
andalso (S==g orelse S==l) ->
try gproc:unreg({p, l, {?MODULE,Key}})
catch
error:badarg -> ok
end,
gen_server:cast(?SERVER, {unsubscribe, self(), Key}).
%%--------------------------------------------------------------------
%% @doc
%% Starts the server
%%
%% @spec start_link() -> {ok, Pid} | ignore | {error, Error}
%% @end
%%--------------------------------------------------------------------
start_link() ->
Me = self(),
_ = case ets:info(?TAB, owner) of
undefined ->
ets:new(?TAB, [ordered_set, protected, named_table,
{heir, self(), []}]);
Me ->
ok
end,
{ok, Pid} = proc_lib:start_link(?MODULE, init, [Me]),
ets:give_away(?TAB, Pid, []),
{ok, Pid}.
%%%===================================================================
%%% gen_server callbacks
%%%===================================================================
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Initializes the server
%%
%% @spec init(Args) -> {ok, State} |
%% {ok, State, Timeout} |
%% ignore |
%% {stop, Reason}
%% @end
%%--------------------------------------------------------------------
init(Parent) ->
process_flag(priority, high),
register(?SERVER, self()),
proc_lib:init_ack(Parent, {ok, self()}),
receive {'ETS-TRANSFER',?TAB,_,_} -> ok end,
gen_server:enter_loop(?MODULE, [], #state{}).
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Handling call messages
%%
%% @spec handle_call(Request, From, State) ->
%% {reply, Reply, State} |
%% {reply, Reply, State, Timeout} |
%% {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, Reply, State} |
%% {stop, Reason, State}
%% @end
%%--------------------------------------------------------------------
handle_call(_Request, _From, State) ->
Reply = ok,
{reply, Reply, State}.
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Handling cast messages
%%
%% @spec handle_cast(Msg, State) -> {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State}
%% @end
%%--------------------------------------------------------------------
handle_cast({subscribe, Pid, Key}, State) ->
Status = gproc:where(Key),
add_subscription(Pid, Key),
do_monitor(Key, Status),
Pid ! {?MODULE, Key, Status},
monitor_pid(Pid),
{noreply, State};
handle_cast({unsubscribe, Pid, Key}, State) ->
del_subscription(Pid, Key),
{noreply, State}.
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Handling all non call/cast messages
%%
%% @spec handle_info(Info, State) -> {noreply, State} |
%% {noreply, State, Timeout} |
%% {stop, Reason, State}
%% @end
%%--------------------------------------------------------------------
handle_info({gproc, unreg, _Ref, Name}, State) ->
ets:delete(?TAB, {m, Name}),
notify(Name, undefined),
do_monitor(Name, undefined),
{noreply, State};
handle_info({gproc, {migrated,ToPid}, _Ref, Name}, State) ->
ets:delete(?TAB, {m, Name}),
notify(Name, {migrated, ToPid}),
do_monitor(Name, ToPid),
{noreply, State};
handle_info({gproc, _, registered, {{T,_,_} = Name, Pid, _}}, State)
when T==n; T==a ->
ets:delete(?TAB, {w, Name}),
notify(Name, Pid),
do_monitor(Name, Pid),
{noreply, State};
handle_info({'DOWN', _, process, Pid, _}, State) ->
pid_is_down(Pid),
{noreply, State};
handle_info(_Msg, State) ->
{noreply, State}.
%%--------------------------------------------------------------------
%% @private
%% @doc
%% This function is called by a gen_server when it is about to
%% terminate. It should be the opposite of Module:init/1 and do any
%% necessary cleaning up. When it returns, the gen_server terminates
%% with Reason. The return value is ignored.
%%
%% @spec terminate(Reason, State) -> void()
%% @end
%%--------------------------------------------------------------------
terminate(_Reason, _State) ->
ok.
%%--------------------------------------------------------------------
%% @private
%% @doc
%% Convert process state when code is changed
%%
%% @spec code_change(OldVsn, State, Extra) -> {ok, NewState}
%% @end
%%--------------------------------------------------------------------
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%%%===================================================================
%%% Internal functions
%%%===================================================================
add_subscription(Pid, {_,_,_} = Key) when is_pid(Pid) ->
ets:insert(?TAB, [{{s, Key, Pid}}, {{r, Pid, Key}}]).
del_subscription(Pid, Key) ->
ets:delete(?TAB, {{s, Key, Pid}}),
ets:delete(?TAB, {{r, Pid, Key}}),
maybe_cancel_wait(Key).
do_monitor(Name, undefined) ->
case ets:member(?TAB, {w, Name}) of
false ->
Ref = gproc:nb_wait(Name),
ets:insert(?TAB, {{w, Name}, Ref})
end;
do_monitor(Name, Pid) when is_pid(Pid) ->
case ets:member(?TAB, {m, Name}) of
true ->
ok;
_ ->
Ref = gproc:monitor(Name),
ets:insert(?TAB, {{m, Name}, Ref})
end.
monitor_pid(Pid) when is_pid(Pid) ->
case ets:member(?TAB, {p,Pid}) of
false ->
Ref = erlang:monitor(process, Pid),
ets:insert(?TAB, {{p,Pid}, Ref});
true ->
ok
end.
pid_is_down(Pid) ->
Keys = ets:select(?TAB, [{ {{r, Pid, '$1'}}, [], ['$1'] }]),
ets:select_delete(?TAB, [{ {{r, Pid, '$1'}}, [], [true] }]),
lists:foreach(fun(K) ->
ets:delete(?TAB, {s,K,Pid}),
maybe_cancel_wait(K)
end, Keys),
ets:delete(?TAB, {p, Pid}).
maybe_cancel_wait(K) ->
case ets:next(?TAB, {s,K}) of
{s,K,P} when is_pid(P) ->
ok;
_ ->
gproc:cancel_wait_or_monitor(K),
ets:delete(?TAB, {m, K}),
ets:delete(?TAB, {w, K})
end.
notify(Name, Where) ->
gproc:send({p, l, {?MODULE, Name}}, {?MODULE, Name, Where}).
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