%%
%% %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(pg2).
-export([create/1, delete/1, join/2, leave/2]).
-export([get_members/1, get_local_members/1]).
-export([get_closest_pid/1, which_groups/0]).
-export([start/0,start_link/0,init/1,handle_call/3,handle_cast/2,handle_info/2,
terminate/2]).
%%% As of R13B03 monitors are used instead of links.
%%%
%%% Exported functions
%%%
-spec start_link() -> {'ok', pid()} | {'error', term()}.
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
-spec start() -> {'ok', pid()} | {'error', term()}.
start() ->
ensure_started().
-spec create(term()) -> 'ok'.
create(Name) ->
ensure_started(),
case ets:member(pg2_table, {group, Name}) of
false ->
global:trans({{?MODULE, Name}, self()},
fun() ->
gen_server:multi_call(?MODULE, {create, Name})
end),
ok;
true ->
ok
end.
-type name() :: term().
-spec delete(name()) -> 'ok'.
delete(Name) ->
ensure_started(),
global:trans({{?MODULE, Name}, self()},
fun() ->
gen_server:multi_call(?MODULE, {delete, Name})
end),
ok.
-spec join(name(), pid()) -> 'ok' | {'error', {'no_such_group', term()}}.
join(Name, Pid) when is_pid(Pid) ->
ensure_started(),
case ets:member(pg2_table, {group, Name}) of
false ->
{error, {no_such_group, Name}};
true ->
global:trans({{?MODULE, Name}, self()},
fun() ->
gen_server:multi_call(?MODULE,
{join, Name, Pid})
end),
ok
end.
-spec leave(name(), pid()) -> 'ok' | {'error', {'no_such_group', name()}}.
leave(Name, Pid) when is_pid(Pid) ->
ensure_started(),
case ets:member(pg2_table, {group, Name}) of
false ->
{error, {no_such_group, Name}};
true ->
global:trans({{?MODULE, Name}, self()},
fun() ->
gen_server:multi_call(?MODULE,
{leave, Name, Pid})
end),
ok
end.
-type get_members_ret() :: [pid()] | {'error', {'no_such_group', name()}}.
-spec get_members(name()) -> get_members_ret().
get_members(Name) ->
ensure_started(),
case ets:member(pg2_table, {group, Name}) of
true ->
group_members(Name);
false ->
{error, {no_such_group, Name}}
end.
-spec get_local_members(name()) -> get_members_ret().
get_local_members(Name) ->
ensure_started(),
case ets:member(pg2_table, {group, Name}) of
true ->
local_group_members(Name);
false ->
{error, {no_such_group, Name}}
end.
-spec which_groups() -> [name()].
which_groups() ->
ensure_started(),
all_groups().
-type gcp_error_reason() :: {'no_process', term()} | {'no_such_group', term()}.
-spec get_closest_pid(term()) -> pid() | {'error', gcp_error_reason()}.
get_closest_pid(Name) ->
case get_local_members(Name) of
[Pid] ->
Pid;
[] ->
{_,_,X} = erlang:now(),
case get_members(Name) of
[] -> {error, {no_process, Name}};
Members ->
lists:nth((X rem length(Members))+1, Members)
end;
Members when is_list(Members) ->
{_,_,X} = erlang:now(),
lists:nth((X rem length(Members))+1, Members);
Else ->
Else
end.
%%%
%%% Callback functions from gen_server
%%%
-record(state, {}).
-spec init([]) -> {'ok', #state{}}.
init([]) ->
Ns = nodes(),
net_kernel:monitor_nodes(true),
lists:foreach(fun(N) ->
{?MODULE, N} ! {new_pg2, node()},
self() ! {nodeup, N}
end, Ns),
pg2_table = ets:new(pg2_table, [ordered_set, protected, named_table]),
{ok, #state{}}.
-type call() :: {'create', name()}
| {'delete', name()}
| {'join', name(), pid()}
| {'leave', name(), pid()}.
-spec handle_call(call(), _, #state{}) ->
{'reply', 'ok', #state{}}.
handle_call({create, Name}, _From, S) ->
assure_group(Name),
{reply, ok, S};
handle_call({join, Name, Pid}, _From, S) ->
ets:member(pg2_table, {group, Name}) andalso join_group(Name, Pid),
{reply, ok, S};
handle_call({leave, Name, Pid}, _From, S) ->
ets:member(pg2_table, {group, Name}) andalso leave_group(Name, Pid),
{reply, ok, S};
handle_call({delete, Name}, _From, S) ->
delete_group(Name),
{reply, ok, S};
handle_call(Request, From, S) ->
error_logger:warning_msg("The pg2 server received an unexpected message:\n"
"handle_call(~p, ~p, _)\n",
[Request, From]),
{noreply, S}.
-type all_members() :: [[name(),...]].
-type cast() :: {'exchange', node(), all_members()}
| {'del_member', name(), pid()}.
-spec handle_cast(cast(), #state{}) -> {'noreply', #state{}}.
handle_cast({exchange, _Node, List}, S) ->
store(List),
{noreply, S};
handle_cast(_, S) ->
%% Ignore {del_member, Name, Pid}.
{noreply, S}.
-spec handle_info(tuple(), #state{}) -> {'noreply', #state{}}.
handle_info({'DOWN', MonitorRef, process, _Pid, _Info}, S) ->
member_died(MonitorRef),
{noreply, S};
handle_info({nodeup, Node}, S) ->
gen_server:cast({?MODULE, Node}, {exchange, node(), all_members()}),
{noreply, S};
handle_info({new_pg2, Node}, S) ->
gen_server:cast({?MODULE, Node}, {exchange, node(), all_members()}),
{noreply, S};
handle_info(_, S) ->
{noreply, S}.
-spec terminate(term(), #state{}) -> 'ok'.
terminate(_Reason, _S) ->
true = ets:delete(pg2_table),
ok.
%%%
%%% Local functions
%%%
%%% One ETS table, pg2_table, is used for bookkeeping. The type of the
%%% table is ordered_set, and the fast matching of partially
%%% instantiated keys is used extensively.
%%%
%%% {{group, Name}}
%%% Process group Name.
%%% {{ref, Pid}, RPid, MonitorRef, Counter}
%%% {{ref, MonitorRef}, Pid}
%%% Each process has one monitor. Sometimes a process is spawned to
%%% monitor the pid (RPid). Counter is incremented when the Pid joins
%%% some group.
%%% {{member, Name, Pid}, GroupCounter}
%%% {{local_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.
store(List) ->
_ = [assure_group(Name) andalso [join_group(Name, P) || P <- Members] ||
[Name, Members] <- List],
ok.
assure_group(Name) ->
Key = {group, Name},
ets:member(pg2_table, Key) orelse true =:= ets:insert(pg2_table, {Key}).
delete_group(Name) ->
_ = [leave_group(Name, Pid) || Pid <- group_members(Name)],
true = ets:delete(pg2_table, {group, Name}),
ok.
member_died(Ref) ->
[{{ref, Ref}, Pid}] = ets:lookup(pg2_table, {ref, Ref}),
Names = member_groups(Pid),
_ = [leave_group(Name, P) ||
Name <- Names,
P <- member_in_group(Pid, Name)],
%% Kept for backward compatibility with links. Can be removed, eventually.
_ = [gen_server:abcast(nodes(), ?MODULE, {del_member, Name, Pid}) ||
Name <- Names],
ok.
join_group(Name, Pid) ->
Ref_Pid = {ref, Pid},
try _ = ets:update_counter(pg2_table, Ref_Pid, {4, +1})
catch _:_ ->
{RPid, Ref} = do_monitor(Pid),
true = ets:insert(pg2_table, {Ref_Pid, RPid, Ref, 1}),
true = ets:insert(pg2_table, {{ref, Ref}, Pid})
end,
Member_Name_Pid = {member, Name, Pid},
try _ = ets:update_counter(pg2_table, Member_Name_Pid, {2, +1})
catch _:_ ->
true = ets:insert(pg2_table, {Member_Name_Pid, 1}),
_ = [ets:insert(pg2_table, {{local_member, Name, Pid}}) ||
node(Pid) =:= node()],
true = ets:insert(pg2_table, {{pid, Pid, Name}})
end.
leave_group(Name, Pid) ->
Member_Name_Pid = {member, Name, Pid},
try ets:update_counter(pg2_table, Member_Name_Pid, {2, -1}) of
N ->
if
N =:= 0 ->
true = ets:delete(pg2_table, {pid, Pid, Name}),
_ = [ets:delete(pg2_table, {local_member, Name, Pid}) ||
node(Pid) =:= node()],
true = ets:delete(pg2_table, Member_Name_Pid);
true ->
ok
end,
Ref_Pid = {ref, Pid},
case ets:update_counter(pg2_table, Ref_Pid, {4, -1}) of
0 ->
[{Ref_Pid,RPid,Ref,0}] = ets:lookup(pg2_table, Ref_Pid),
true = ets:delete(pg2_table, {ref, Ref}),
true = ets:delete(pg2_table, Ref_Pid),
true = erlang:demonitor(Ref, [flush]),
kill_monitor_proc(RPid, Pid);
_ ->
ok
end
catch _:_ ->
ok
end.
all_members() ->
[[G, group_members(G)] || G <- all_groups()].
group_members(Name) ->
[P ||
[P, N] <- ets:match(pg2_table, {{member, Name, '$1'},'$2'}),
_ <- lists:seq(1, N)].
local_group_members(Name) ->
[P ||
[Pid] <- ets:match(pg2_table, {{local_member, Name, '$1'}}),
P <- member_in_group(Pid, Name)].
member_in_group(Pid, Name) ->
[{{member, Name, Pid}, N}] = ets:lookup(pg2_table, {member, Name, Pid}),
lists:duplicate(N, Pid).
member_groups(Pid) ->
[Name || [Name] <- ets:match(pg2_table, {{pid, Pid, '$1'}})].
all_groups() ->
[N || [N] <- ets:match(pg2_table, {{group,'$1'}})].
ensure_started() ->
case whereis(?MODULE) of
undefined ->
C = {pg2, {?MODULE, start_link, []}, permanent,
1000, worker, [?MODULE]},
supervisor:start_child(kernel_safe_sup, C);
Pg2Pid ->
{ok, Pg2Pid}
end.
kill_monitor_proc(RPid, Pid) ->
RPid =:= Pid orelse exit(RPid, kill).
%% When/if erlang:monitor() returns before trying to connect to the
%% other node this function can be removed.
do_monitor(Pid) ->
case (node(Pid) =:= node()) orelse lists:member(node(Pid), nodes()) of
true ->
%% Assume the node is still up
{Pid, erlang:monitor(process, Pid)};
false ->
F = fun() ->
Ref = erlang:monitor(process, Pid),
receive
{'DOWN', Ref, process, Pid, _Info} ->
exit(normal)
end
end,
erlang:spawn_monitor(F)
end.
