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%% This file is a copy of pg2.erl from the R13B-3 Erlang/OTP
%% distribution, with the following modifications:
%%
%% 1) Process groups are node-local only.
%%
%% 2) Groups are created/deleted implicitly.
%%
%% 3) 'join' and 'leave' are asynchronous.
%%
%% 4) the type specs of the exported non-callback functions have been
%% extracted into a separate, guarded section, and rewritten in
%% old-style spec syntax, for better compatibility with older
%% versions of Erlang/OTP. The remaining type specs have been
%% removed.
%% All modifications are (C) 2010 LShift Ltd.
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1997-2009. All Rights Reserved.
%%
%% 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 online 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.
%%
%% %CopyrightEnd%
%%
-module(pg_local).
-export([join/2, leave/2, get_members/1]).
-export([sync/0]). %% intended for testing only; not part of official API
-export([start/0, start_link/0, init/1, handle_call/3, handle_cast/2,
handle_info/2, terminate/2]).
%%----------------------------------------------------------------------------
-ifdef(use_specs).
-type(name() :: term()).
-spec(start_link/0 :: () -> {'ok', pid()} | {'error', any()}).
-spec(start/0 :: () -> {'ok', pid()} | {'error', any()}).
-spec(join/2 :: (name(), pid()) -> 'ok').
-spec(leave/2 :: (name(), pid()) -> 'ok').
-spec(get_members/1 :: (name()) -> [pid()]).
-spec(sync/0 :: () -> 'ok').
-endif.
%%----------------------------------------------------------------------------
%%% As of R13B03 monitors are used instead of links.
%%%
%%% Exported functions
%%%
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
start() ->
ensure_started().
join(Name, Pid) when is_pid(Pid) ->
ensure_started(),
gen_server:cast(?MODULE, {join, Name, Pid}).
leave(Name, Pid) when is_pid(Pid) ->
ensure_started(),
gen_server:cast(?MODULE, {leave, Name, Pid}).
get_members(Name) ->
ensure_started(),
group_members(Name).
sync() ->
ensure_started(),
gen_server:call(?MODULE, sync).
%%%
%%% Callback functions from gen_server
%%%
-record(state, {}).
init([]) ->
pg_local_table = ets:new(pg_local_table, [ordered_set, protected, named_table]),
{ok, #state{}}.
handle_call(sync, _From, S) ->
{reply, ok, S};
handle_call(Request, From, S) ->
error_logger:warning_msg("The pg_local server received an unexpected message:\n"
"handle_call(~p, ~p, _)\n",
[Request, From]),
{noreply, S}.
handle_cast({join, Name, Pid}, S) ->
join_group(Name, Pid),
{noreply, S};
handle_cast({leave, Name, Pid}, S) ->
leave_group(Name, Pid),
{noreply, S};
handle_cast(_, S) ->
{noreply, S}.
handle_info({'DOWN', MonitorRef, process, _Pid, _Info}, S) ->
member_died(MonitorRef),
{noreply, S};
handle_info(_, S) ->
{noreply, S}.
terminate(_Reason, _S) ->
true = ets:delete(pg_local_table),
ok.
%%%
%%% Local functions
%%%
%%% One ETS table, pg_local_table, is used for bookkeeping. The type of the
%%% table is ordered_set, and the fast matching of partially
%%% instantiated keys is used extensively.
%%%
%%% {{ref, Pid}, MonitorRef, Counter}
%%% {{ref, MonitorRef}, Pid}
%%% Each process has one monitor. Counter is incremented when the
%%% Pid joins some group.
%%% {{member, Name, Pid}, _}
%%% Pid is a member of group Name, GroupCounter is incremented when the
%%% Pid joins the group Name.
%%% {{pid, Pid, Name}}
%%% Pid is a member of group Name.
member_died(Ref) ->
[{{ref, Ref}, Pid}] = ets:lookup(pg_local_table, {ref, Ref}),
Names = member_groups(Pid),
_ = [leave_group(Name, P) ||
Name <- Names,
P <- member_in_group(Pid, Name)],
ok.
join_group(Name, Pid) ->
Ref_Pid = {ref, Pid},
try _ = ets:update_counter(pg_local_table, Ref_Pid, {3, +1})
catch _:_ ->
Ref = erlang:monitor(process, Pid),
true = ets:insert(pg_local_table, {Ref_Pid, Ref, 1}),
true = ets:insert(pg_local_table, {{ref, Ref}, Pid})
end,
Member_Name_Pid = {member, Name, Pid},
try _ = ets:update_counter(pg_local_table, Member_Name_Pid, {2, +1})
catch _:_ ->
true = ets:insert(pg_local_table, {Member_Name_Pid, 1}),
true = ets:insert(pg_local_table, {{pid, Pid, Name}})
end.
leave_group(Name, Pid) ->
Member_Name_Pid = {member, Name, Pid},
try ets:update_counter(pg_local_table, Member_Name_Pid, {2, -1}) of
N ->
if
N =:= 0 ->
true = ets:delete(pg_local_table, {pid, Pid, Name}),
true = ets:delete(pg_local_table, Member_Name_Pid);
true ->
ok
end,
Ref_Pid = {ref, Pid},
case ets:update_counter(pg_local_table, Ref_Pid, {3, -1}) of
0 ->
[{Ref_Pid,Ref,0}] = ets:lookup(pg_local_table, Ref_Pid),
true = ets:delete(pg_local_table, {ref, Ref}),
true = ets:delete(pg_local_table, Ref_Pid),
true = erlang:demonitor(Ref, [flush]),
ok;
_ ->
ok
end
catch _:_ ->
ok
end.
group_members(Name) ->
[P ||
[P, N] <- ets:match(pg_local_table, {{member, Name, '$1'},'$2'}),
_ <- lists:seq(1, N)].
member_in_group(Pid, Name) ->
[{{member, Name, Pid}, N}] = ets:lookup(pg_local_table, {member, Name, Pid}),
lists:duplicate(N, Pid).
member_groups(Pid) ->
[Name || [Name] <- ets:match(pg_local_table, {{pid, Pid, '$1'}})].
ensure_started() ->
case whereis(?MODULE) of
undefined ->
C = {pg_local, {?MODULE, start_link, []}, permanent,
16#ffffffff, worker, [?MODULE]},
supervisor:start_child(kernel_safe_sup, C);
PgLocalPid ->
{ok, PgLocalPid}
end.
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