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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) 2010-2020 VMware, Inc. or its affiliates.
%% %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 https://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, in_group/2]).
%% intended for testing only; not part of official API
-export([sync/0, clear/0]).
-export([start/0, start_link/0, init/1, handle_call/3, handle_cast/2,
handle_info/2, terminate/2]).
%%----------------------------------------------------------------------------
-type name() :: term().
%%----------------------------------------------------------------------------
-define(TABLE, pg_local_table).
%%%
%%% Exported functions
%%%
-spec start_link() -> {'ok', pid()} | {'error', any()}.
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
-spec start() -> {'ok', pid()} | {'error', any()}.
start() ->
ensure_started().
-spec join(name(), pid()) -> 'ok'.
join(Name, Pid) when is_pid(Pid) ->
_ = ensure_started(),
gen_server:cast(?MODULE, {join, Name, Pid}).
-spec leave(name(), pid()) -> 'ok'.
leave(Name, Pid) when is_pid(Pid) ->
_ = ensure_started(),
gen_server:cast(?MODULE, {leave, Name, Pid}).
-spec get_members(name()) -> [pid()].
get_members(Name) ->
_ = ensure_started(),
group_members(Name).
-spec in_group(name(), pid()) -> boolean().
in_group(Name, Pid) ->
_ = ensure_started(),
%% The join message is a cast and thus can race, but we want to
%% keep it that way to be fast in the common case.
case member_present(Name, Pid) of
true -> true;
false -> sync(),
member_present(Name, Pid)
end.
-spec sync() -> 'ok'.
sync() ->
_ = ensure_started(),
gen_server:call(?MODULE, sync, infinity).
clear() ->
_ = ensure_started(),
gen_server:call(?MODULE, clear, infinity).
%%%
%%% Callback functions from gen_server
%%%
-record(state, {}).
init([]) ->
?TABLE = ets:new(?TABLE, [ordered_set, protected, named_table]),
{ok, #state{}}.
handle_call(sync, _From, S) ->
{reply, ok, S};
handle_call(clear, _From, S) ->
ets:delete_all_objects(?TABLE),
{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, Pid),
{noreply, S};
handle_info(_, S) ->
{noreply, S}.
terminate(_Reason, _S) ->
true = ets:delete(?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, Pid) ->
case ets:lookup(?TABLE, {ref, Ref}) of
[{{ref, Ref}, Pid}] ->
leave_all_groups(Pid);
%% in case the key has already been removed
%% we can clean up using the value from the DOWN message
_ ->
leave_all_groups(Pid)
end,
ok.
leave_all_groups(Pid) ->
Names = member_groups(Pid),
_ = [leave_group(Name, P) ||
Name <- Names,
P <- member_in_group(Pid, Name)].
join_group(Name, Pid) ->
Ref_Pid = {ref, Pid},
try _ = ets:update_counter(?TABLE, Ref_Pid, {3, +1})
catch _:_ ->
Ref = erlang:monitor(process, Pid),
true = ets:insert(?TABLE, {Ref_Pid, Ref, 1}),
true = ets:insert(?TABLE, {{ref, Ref}, Pid})
end,
Member_Name_Pid = {member, Name, Pid},
try _ = ets:update_counter(?TABLE, Member_Name_Pid, {2, +1})
catch _:_ ->
true = ets:insert(?TABLE, {Member_Name_Pid, 1}),
true = ets:insert(?TABLE, {{pid, Pid, Name}})
end.
leave_group(Name, Pid) ->
Member_Name_Pid = {member, Name, Pid},
try ets:update_counter(?TABLE, Member_Name_Pid, {2, -1}) of
N ->
if
N =:= 0 ->
true = ets:delete(?TABLE, {pid, Pid, Name}),
true = ets:delete(?TABLE, Member_Name_Pid);
true ->
ok
end,
Ref_Pid = {ref, Pid},
case ets:update_counter(?TABLE, Ref_Pid, {3, -1}) of
0 ->
[{Ref_Pid,Ref,0}] = ets:lookup(?TABLE, Ref_Pid),
true = ets:delete(?TABLE, {ref, Ref}),
true = ets:delete(?TABLE, Ref_Pid),
true = erlang:demonitor(Ref, [flush]),
ok;
_ ->
ok
end
catch _:_ ->
ok
end.
group_members(Name) ->
[P ||
[P, N] <- ets:match(?TABLE, {{member, Name, '$1'},'$2'}),
_ <- lists:seq(1, N)].
member_in_group(Pid, Name) ->
[{{member, Name, Pid}, N}] = ets:lookup(?TABLE, {member, Name, Pid}),
lists:duplicate(N, Pid).
member_present(Name, Pid) ->
case ets:lookup(?TABLE, {member, Name, Pid}) of
[_] -> true;
[] -> false
end.
member_groups(Pid) ->
[Name || [Name] <- ets:match(?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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