summaryrefslogtreecommitdiff
path: root/lib/kernel/src/pg2.erl
blob: ab98181b2a0ef1805e2bc118f722bf26a6e52bd6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1997-2013. All Rights Reserved.
%%
%% 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.
%%
%% %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', any()}.

start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

-spec start() -> {'ok', pid()} | {'error', any()}.

start() ->
    ensure_started().

-type name() :: any().

-spec create(Name :: name()) -> '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.

-spec delete(Name :: 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 :: pid()) -> 'ok' | {'error', {'no_such_group', Name}}
      when Name :: name().

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 :: pid()) -> 'ok' | {'error', {'no_such_group', Name}}
      when Name :: 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.

-spec get_members(Name) -> [pid()] | {'error', {'no_such_group', Name}}
      when Name :: name().

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) -> [pid()] | {'error', {'no_such_group', Name}}
      when Name :: name().

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 :: name()].

which_groups() ->
    _ = ensure_started(),
    all_groups().

-spec get_closest_pid(Name) ->  pid() | {'error', Reason} when
      Name :: name(),
      Reason ::  {'no_process', Name} | {'no_such_group', Name}.

get_closest_pid(Name) ->
    case get_local_members(Name) of
        [Pid] ->
            Pid;
        [] ->
            case get_members(Name) of
                [] -> {error, {no_process, Name}};
                Members ->
                    random_element(Members)
            end;
        Members when is_list(Members) ->
            random_element(Members);
        Else ->
            Else
    end.

random_element(List) ->
    X = abs(erlang:monotonic_time()
		bxor erlang:unique_integer()),
    lists:nth((X rem length(List)) + 1, List).

%%%
%%% Callback functions from gen_server
%%%

-record(state, {}).

-type state() :: #state{}.

-spec init(Arg :: []) -> {'ok', state()}.

init([]) ->
    Ns = nodes(),
    ok = 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{}}.

-spec handle_call(Call :: {'create', Name}
                        | {'delete', Name}
                        | {'join', Name, Pid :: pid()}
                        | {'leave', Name, Pid :: pid()},
                  From :: {pid(),Tag :: any()},
                  State :: state()) -> {'reply', 'ok', state()}
      when Name :: name().

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}.

-spec handle_cast(Cast :: {'exchange', node(), Names :: [[Name,...]]}
                        | {'del_member', Name, Pid :: pid()},
                  State :: state()) -> {'noreply', state()}
      when Name :: name().

handle_cast({exchange, _Node, List}, S) ->
    store(List),
    {noreply, S};
handle_cast(_, S) ->
    %% Ignore {del_member, Name, Pid}.
    {noreply, S}.

-spec handle_info(Tuple :: tuple(), State :: 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(Reason :: any(), State :: 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 -- group_members(Name)]) ||
            [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}), true
    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) ->
    case ets:lookup(pg2_table, {member, Name, Pid}) of
        [] -> [];
        [{{member, Name, Pid}, N}] ->
            lists:duplicate(N, Pid)
    end.

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.