aboutsummaryrefslogtreecommitdiffstats
path: root/lib/stdlib/src/gen_event.erl
blob: 7629e88fbf7357d0cdbef4f741c50cb98d9c29a5 (plain) (blame)
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
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2013. 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(gen_event).

%%% 
%%% A general event handler.
%%% Several handlers (functions) can be added.
%%% Each handler holds a state and will be called
%%% for every event received of the handler.
%%% 

%%% Modified by Magnus.
%%%       Take care of fault situations and made notify asynchronous.
%%% Re-written by Joe with new functional interface !
%%% Modified by Martin - uses proc_lib, sys and gen!


-export([start/0, start/1, start_link/0, start_link/1, stop/1, notify/2, 
	 sync_notify/2,
	 add_handler/3, add_sup_handler/3, delete_handler/3, swap_handler/3,
	 swap_sup_handler/3, which_handlers/1, call/3, call/4, wake_hib/4]).

-export([init_it/6,
	 system_continue/3,
	 system_terminate/4,
	 system_code_change/4,
	 format_status/2]).

-export_type([handler/0, handler_args/0, add_handler_ret/0,
              del_handler_ret/0]).

-import(error_logger, [error_msg/2]).

-define(reply(X), From ! {element(2,Tag), X}).

-record(handler, {module             :: atom(),
		  id = false,
		  state,
		  supervised = false :: 'false' | pid()}).

%%%=========================================================================
%%%  API
%%%=========================================================================

%% gen_event:start(Handler) -> {ok, Pid} | {error, What}
%%   gen_event:add_handler(Handler, Mod, Args) -> ok | Other
%%      gen_event:notify(Handler, Event) -> ok
%%      gen_event:call(Handler, Mod, Query) -> {ok, Val} | {error, Why}
%%      gen_event:call(Handler, Mod, Query, Timeout) -> {ok, Val} | {error, Why}
%%   gen_event:delete_handler(Handler, Mod, Args) -> Val
%%   gen_event:swap_handler(Handler, {OldMod, Args1}, {NewMod, Args2}) -> ok
%%   gen_event:which_handler(Handler) -> [Mod]
%% gen_event:stop(Handler) -> ok 

-callback init(InitArgs :: term()) ->
    {ok, State :: term()} |
    {ok, State :: term(), hibernate} |
    {error, Reason :: term()}.
-callback handle_event(Event :: term(), State :: term()) ->
    {ok, NewState :: term()} |
    {ok, NewState :: term(), hibernate} |
    {swap_handler, Args1 :: term(), NewState :: term(),
     Handler2 :: (atom() | {atom(), Id :: term()}), Args2 :: term()} |
    remove_handler.
-callback handle_call(Request :: term(), State :: term()) ->
    {ok, Reply :: term(), NewState :: term()} |
    {ok, Reply :: term(), NewState :: term(), hibernate} |
    {swap_handler, Reply :: term(), Args1 :: term(), NewState :: term(),
     Handler2 :: (atom() | {atom(), Id :: term()}), Args2 :: term()} |
    {remove_handler, Reply :: term()}.
-callback handle_info(Info :: term(), State :: term()) ->
    {ok, NewState :: term()} |
    {ok, NewState :: term(), hibernate} |
    {swap_handler, Args1 :: term(), NewState :: term(),
     Handler2 :: (atom() | {atom(), Id :: term()}), Args2 :: term()} |
    remove_handler.
-callback terminate(Args :: (term() | {stop, Reason :: term()} |
                             stop | remove_handler |
                             {error, {'EXIT', Reason :: term()}} |
                             {error, term()}),
                    State :: term()) ->
    term().
-callback code_change(OldVsn :: (term() | {down, term()}),
                      State :: term(), Extra :: term()) ->
    {ok, NewState :: term()}.

%%---------------------------------------------------------------------------

-type handler()          :: atom() | {atom(), term()}.
-type handler_args()     :: term().
-type add_handler_ret()  :: ok | term() | {'EXIT',term()}.
-type del_handler_ret()  :: ok | term() | {'EXIT',term()}.

-type emgr_name() :: {'local', atom()} | {'global', atom()}
		   | {'via', atom(), term()}.
-type emgr_ref()  :: atom() | {atom(), atom()} |  {'global', atom()}
		   | {'via', atom(), term()} | pid().
-type start_ret() :: {'ok', pid()} | {'error', term()}.

%%---------------------------------------------------------------------------

-define(NO_CALLBACK, 'no callback module').

-spec start() -> start_ret().
start() ->
    gen:start(?MODULE, nolink, ?NO_CALLBACK, [], []).

-spec start(emgr_name()) -> start_ret().
start(Name) ->
    gen:start(?MODULE, nolink, Name, ?NO_CALLBACK, [], []).

-spec start_link() -> start_ret().
start_link() ->
    gen:start(?MODULE, link, ?NO_CALLBACK, [], []).

-spec start_link(emgr_name()) -> start_ret().
start_link(Name) ->
    gen:start(?MODULE, link, Name, ?NO_CALLBACK, [], []).

%% -spec init_it(pid(), 'self' | pid(), emgr_name(), module(), [term()], [_]) -> 
init_it(Starter, self, Name, Mod, Args, Options) ->
    init_it(Starter, self(), Name, Mod, Args, Options);
init_it(Starter, Parent, Name0, _, _, Options) ->
    process_flag(trap_exit, true),
    Debug = gen:debug_options(Options),
    proc_lib:init_ack(Starter, {ok, self()}),
    Name = name(Name0),
    loop(Parent, Name, [], Debug, false).

name({local,Name}) -> Name;
name({global,Name}) -> Name;
name({via,_, Name}) -> Name;
name(Pid) when is_pid(Pid) -> Pid.

-spec add_handler(emgr_ref(), handler(), term()) -> term().
add_handler(M, Handler, Args) -> rpc(M, {add_handler, Handler, Args}).

-spec add_sup_handler(emgr_ref(), handler(), term()) -> term().
add_sup_handler(M, Handler, Args)  ->
    rpc(M, {add_sup_handler, Handler, Args, self()}).

-spec notify(emgr_ref(), term()) -> 'ok'.
notify(M, Event) -> send(M, {notify, Event}). 

-spec sync_notify(emgr_ref(), term()) -> 'ok'.
sync_notify(M, Event) -> rpc(M, {sync_notify, Event}).

-spec call(emgr_ref(), handler(), term()) -> term().
call(M, Handler, Query) -> call1(M, Handler, Query).

-spec call(emgr_ref(), handler(), term(), timeout()) -> term().
call(M, Handler, Query, Timeout) -> call1(M, Handler, Query, Timeout).

-spec delete_handler(emgr_ref(), handler(), term()) -> term().
delete_handler(M, Handler, Args) -> rpc(M, {delete_handler, Handler, Args}).

-spec swap_handler(emgr_ref(), {handler(), term()}, {handler(), term()}) ->
	    'ok' | {'error', term()}.
swap_handler(M, {H1, A1}, {H2, A2}) -> rpc(M, {swap_handler, H1, A1, H2, A2}).

-spec swap_sup_handler(emgr_ref(), {handler(), term()}, {handler(), term()}) ->
	    'ok' | {'error', term()}.
swap_sup_handler(M, {H1, A1}, {H2, A2}) ->
    rpc(M, {swap_sup_handler, H1, A1, H2, A2, self()}).

-spec which_handlers(emgr_ref()) -> [handler()].
which_handlers(M) -> rpc(M, which_handlers).

-spec stop(emgr_ref()) -> 'ok'.
stop(M) -> rpc(M, stop).

rpc(M, Cmd) -> 
    {ok, Reply} = gen:call(M, self(), Cmd, infinity),
    Reply.

call1(M, Handler, Query) ->
    Cmd = {call, Handler, Query},
    try gen:call(M, self(), Cmd) of
	{ok, Res} ->
	    Res
    catch
	exit:Reason ->
	    exit({Reason, {?MODULE, call, [M, Handler, Query]}})
    end.

call1(M, Handler, Query, Timeout) ->
    Cmd = {call, Handler, Query},
    try gen:call(M, self(), Cmd, Timeout) of
	{ok, Res} ->
	    Res
    catch
	exit:Reason ->
	    exit({Reason, {?MODULE, call, [M, Handler, Query, Timeout]}})
    end.

send({global, Name}, Cmd) ->
    catch global:send(Name, Cmd),
    ok;
send({via, Mod, Name}, Cmd) ->
    catch Mod:send(Name, Cmd),
    ok;
send(M, Cmd) ->
    M ! Cmd,
    ok.

loop(Parent, ServerName, MSL, Debug, true) ->
     proc_lib:hibernate(?MODULE, wake_hib, [Parent, ServerName, MSL, Debug]);
loop(Parent, ServerName, MSL, Debug, _) ->
    fetch_msg(Parent, ServerName, MSL, Debug, false).

wake_hib(Parent, ServerName, MSL, Debug) ->
    fetch_msg(Parent, ServerName, MSL, Debug, true).

fetch_msg(Parent, ServerName, MSL, Debug, Hib) ->
    receive
	{system, From, get_state} ->
	    States = [{Mod,Id,State} || #handler{module=Mod, id=Id, state=State} <- MSL],
	    sys:handle_system_msg(get_state, From, Parent, ?MODULE, Debug,
				  {States, [ServerName, MSL, Hib]}, Hib);
	{system, From, {replace_state, StateFun}} ->
	    {NMSL, NStates} =
		lists:unzip([begin
				 Cur = {Mod,Id,State},
				 try
				     NState = {Mod,Id,NS} = StateFun(Cur),
				     {HS#handler{state=NS}, NState}
				 catch
				     _:_ ->
					 {HS, Cur}
				 end
			     end || #handler{module=Mod, id=Id, state=State}=HS <- MSL]),
	    sys:handle_system_msg(replace_state, From, Parent, ?MODULE, Debug,
				  {NStates, [ServerName, NMSL, Hib]}, Hib);
	{system, From, Req} ->
	    sys:handle_system_msg(Req, From, Parent, ?MODULE, Debug,
				  [ServerName, MSL, Hib],Hib);
	{'EXIT', Parent, Reason} ->
	    terminate_server(Reason, Parent, MSL, ServerName);
	Msg when Debug =:= [] ->
	    handle_msg(Msg, Parent, ServerName, MSL, []);
	Msg ->
	    Debug1 = sys:handle_debug(Debug, fun print_event/3,
				      ServerName, {in, Msg}),
	    handle_msg(Msg, Parent, ServerName, MSL, Debug1)
    end.

handle_msg(Msg, Parent, ServerName, MSL, Debug) ->
    case Msg of
	{notify, Event} ->
	    {Hib,MSL1} = server_notify(Event, handle_event, MSL, ServerName),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, {sync_notify, Event}} ->
	    {Hib, MSL1} = server_notify(Event, handle_event, MSL, ServerName),
	    ?reply(ok),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{'EXIT', From, Reason} ->
	    MSL1 = handle_exit(From, Reason, MSL, ServerName),
	    loop(Parent, ServerName, MSL1, Debug, false);
	{From, Tag, {call, Handler, Query}} ->
	    {Hib, Reply, MSL1} = server_call(Handler, Query, MSL, ServerName),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, {add_handler, Handler, Args}} ->
	    {Hib, Reply, MSL1} = server_add_handler(Handler, Args, MSL),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, {add_sup_handler, Handler, Args, SupP}} ->
	    {Hib, Reply, MSL1} = server_add_sup_handler(Handler, Args, MSL, SupP),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, {delete_handler, Handler, Args}} ->
	    {Reply, MSL1} = server_delete_handler(Handler, Args, MSL,
						  ServerName),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, false);
	{From, Tag, {swap_handler, Handler1, Args1, Handler2, Args2}} ->
	    {Hib, Reply, MSL1} = server_swap_handler(Handler1, Args1, Handler2,
						     Args2, MSL, ServerName),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, {swap_sup_handler, Handler1, Args1, Handler2, Args2,
		     Sup}} ->
	    {Hib, Reply, MSL1} = server_swap_handler(Handler1, Args1, Handler2,
						Args2, MSL, Sup, ServerName),
	    ?reply(Reply),
	    loop(Parent, ServerName, MSL1, Debug, Hib);
	{From, Tag, stop} ->
	    catch terminate_server(normal, Parent, MSL, ServerName),
	    ?reply(ok);
	{From, Tag, which_handlers} ->
	    ?reply(the_handlers(MSL)),
	    loop(Parent, ServerName, MSL, Debug, false);
	{From, Tag, get_modules} ->
	    ?reply(get_modules(MSL)),
	    loop(Parent, ServerName, MSL, Debug, false);
	Other  ->
	    {Hib, MSL1} = server_notify(Other, handle_info, MSL, ServerName),
	    loop(Parent, ServerName, MSL1, Debug, Hib)
    end.

terminate_server(Reason, Parent, MSL, ServerName) ->
    stop_handlers(MSL, ServerName),
    do_unlink(Parent, MSL),
    exit(Reason).

%% unlink the supervisor process of all supervised handlers.
%% We do not want a handler supervisor to EXIT due to the
%% termination of the event manager (server).
%% Do not unlink Parent !
do_unlink(Parent, MSL) ->
    lists:foreach(fun(Handler) when Handler#handler.supervised =:= Parent ->
			  true;
		     (Handler) when is_pid(Handler#handler.supervised) ->
			  unlink(Handler#handler.supervised),
			  true;
		     (_) ->
			  true
		  end,
		  MSL).

%% First terminate the supervised (if exists) handlers and
%% then inform other handlers.
%% We do not know if any handler really is interested but it
%% may be so !
handle_exit(From, Reason, MSL, SName) ->
    MSL1 = terminate_supervised(From, Reason, MSL, SName),
    {_,MSL2}=server_notify({'EXIT', From, Reason}, handle_info, MSL1, SName),
    MSL2.

terminate_supervised(Pid, Reason, MSL, SName) ->
    F = fun(Ha) when Ha#handler.supervised =:= Pid ->
		do_terminate(Ha#handler.module,
			     Ha,
			     {stop,Reason},
			     Ha#handler.state,
			     {parent_terminated, {Pid,Reason}},
			     SName,
			     shutdown),
		false;
	   (_) ->
		true
	end,
    lists:filter(F, MSL).

%%-----------------------------------------------------------------
%% Callback functions for system messages handling.
%%-----------------------------------------------------------------
system_continue(Parent, Debug, [ServerName, MSL, Hib]) ->
    loop(Parent, ServerName, MSL, Debug, Hib).

-spec system_terminate(_, _, _, [_]) -> no_return().
system_terminate(Reason, Parent, _Debug, [ServerName, MSL, _Hib]) ->
    terminate_server(Reason, Parent, MSL, ServerName).

%%-----------------------------------------------------------------
%% Module here is sent in the system msg change_code.  It specifies
%% which module should be changed.
%%-----------------------------------------------------------------
system_code_change([ServerName, MSL, Hib], Module, OldVsn, Extra) ->
    MSL1 = lists:zf(fun(H) when H#handler.module =:= Module ->
			    {ok, NewState} =
				Module:code_change(OldVsn,
						   H#handler.state, Extra),
			    {true, H#handler{state = NewState}};
		       (_) -> true
		    end,
		    MSL),
    {ok, [ServerName, MSL1, Hib]}.

%%-----------------------------------------------------------------
%% Format debug messages.  Print them as the call-back module sees
%% them, not as the real erlang messages.  Use trace for that.
%%-----------------------------------------------------------------
print_event(Dev, {in, Msg}, Name) ->
    case Msg of
	{notify, Event} ->
	    io:format(Dev, "*DBG* ~p got event ~p~n", [Name, Event]);
	{_,_,{call, Handler, Query}} ->
	    io:format(Dev, "*DBG* ~p(~p) got call ~p~n",
		      [Name, Handler, Query]);
	_ ->
	    io:format(Dev, "*DBG* ~p got ~p~n", [Name, Msg])
    end;
print_event(Dev, Dbg, Name) ->
    io:format(Dev, "*DBG* ~p : ~p~n", [Name, Dbg]).


%% server_add_handler(Handler, Args, MSL) -> {Ret, MSL'}.
%%   where MSL = [#handler{}]
%%   Ret goes to the top level MSL' is the new internal state of the
%%   event handler

server_add_handler({Mod,Id}, Args, MSL) ->
    Handler = #handler{module = Mod,
		       id = Id},
    server_add_handler(Mod, Handler, Args, MSL);
server_add_handler(Mod, Args, MSL) -> 
    Handler = #handler{module = Mod},
    server_add_handler(Mod, Handler, Args, MSL).

server_add_handler(Mod, Handler, Args, MSL) ->
    case catch Mod:init(Args) of
        {ok, State} ->
	    {false, ok, [Handler#handler{state = State}|MSL]};
        {ok, State, hibernate} ->
	    {true, ok, [Handler#handler{state = State}|MSL]};
        Other ->
            {false, Other, MSL}
    end.

%% Set up a link to the supervising process.
%% (Ought to be unidirected links here, Erl5.0 !!)
%% NOTE: This link will not be removed then the
%% handler is removed in case another handler has
%% own link to this process.
server_add_sup_handler({Mod,Id}, Args, MSL, Parent) ->
    link(Parent),
    Handler = #handler{module = Mod,
		       id = Id,
		       supervised = Parent},
    server_add_handler(Mod, Handler, Args, MSL);
server_add_sup_handler(Mod, Args, MSL, Parent) -> 
    link(Parent),
    Handler = #handler{module = Mod,
		       supervised = Parent},
    server_add_handler(Mod, Handler, Args, MSL).

%% server_delete_handler(HandlerId, Args, MSL) -> {Ret, MSL'}

server_delete_handler(HandlerId, Args, MSL, SName) -> 
    case split(HandlerId, MSL) of
	{Mod, Handler, MSL1} ->
	    {do_terminate(Mod, Handler, Args,
			  Handler#handler.state, delete, SName, normal),
	     MSL1};
	error ->
	    {{error, module_not_found}, MSL}
    end.

%% server_swap_handler(Handler1, Args1, Handler2, Args2, MSL, SN) -> MSL'
%% server_swap_handler(Handler1, Args1, Handler2, Args2, MSL, Sup, SN) -> MSL'

server_swap_handler(Handler1, Args1, Handler2, Args2, MSL, SName) ->
    {State2, Sup, MSL1} = split_and_terminate(Handler1, Args1, MSL,
					      SName, Handler2, false),
    case s_s_h(Sup, Handler2, {Args2, State2}, MSL1) of
	{Hib, ok, MSL2} ->
	    {Hib, ok, MSL2};
	{Hib, What, MSL2} ->
	    {Hib, {error, What}, MSL2}
    end.

server_swap_handler(Handler1, Args1, Handler2, Args2, MSL, Sup, SName) ->
    {State2, _, MSL1} = split_and_terminate(Handler1, Args1, MSL,
					    SName, Handler2, Sup),
    case s_s_h(Sup, Handler2, {Args2, State2}, MSL1) of
	{Hib, ok, MSL2} ->
	    {Hib, ok, MSL2};
	{Hib, What, MSL2} ->
	    {Hib, {error, What}, MSL2}
    end.

s_s_h(false, Handler, Args, MSL) ->
    server_add_handler(Handler, Args, MSL);
s_s_h(Pid, Handler, Args, MSL) ->
    server_add_sup_handler(Handler, Args, MSL, Pid).

split_and_terminate(HandlerId, Args, MSL, SName, Handler2, Sup) ->
    case split(HandlerId, MSL) of
	{Mod, Handler, MSL1} ->
	    OldSup = Handler#handler.supervised,
	    NewSup = if
			 not Sup -> OldSup;
			 true    -> Sup
		     end,
	    {do_terminate(Mod, Handler, Args,
			  Handler#handler.state, swapped, SName,
			  {swapped, Handler2, NewSup}),
	     OldSup,
	     MSL1};
	error ->
            {error, false, MSL}
    end.

%% server_notify(Event, Func, MSL, SName) -> MSL'

server_notify(Event, Func, [Handler|T], SName) -> 
    case server_update(Handler, Func, Event, SName) of
	{ok, Handler1} ->
	    {Hib, NewHandlers} = server_notify(Event, Func, T, SName),
	    {Hib, [Handler1|NewHandlers]};
	{hibernate, Handler1} ->
	    {_Hib, NewHandlers} = server_notify(Event, Func, T, SName),
	    {true, [Handler1|NewHandlers]};
	no ->
	    server_notify(Event, Func, T, SName)
    end;
server_notify(_, _, [], _) ->
    {false, []}.

%% server_update(Handler, Func, Event, ServerName) -> Handler1 | no

server_update(Handler1, Func, Event, SName) ->
    Mod1 = Handler1#handler.module,
    State = Handler1#handler.state,
    case catch Mod1:Func(Event, State) of
	{ok, State1} -> 
	    {ok, Handler1#handler{state = State1}};
	{ok, State1, hibernate} -> 
	    {hibernate, Handler1#handler{state = State1}};
	{swap_handler, Args1, State1, Handler2, Args2} ->
	    do_swap(Mod1, Handler1, Args1, State1, Handler2, Args2, SName);
	remove_handler ->
	    do_terminate(Mod1, Handler1, remove_handler, State,
			 remove, SName, normal),
	    no;
	Other ->
	    do_terminate(Mod1, Handler1, {error, Other}, State,
			 Event, SName, crash),
	    no
    end.

do_swap(Mod1, Handler1, Args1, State1, Handler2, Args2, SName) ->
    %% finalise the existing handler
    State2 = do_terminate(Mod1, Handler1, Args1, State1,
			  swapped, SName,
			  {swapped, Handler2, Handler1#handler.supervised}),
    {Mod2, Handler} = new_handler(Handler2, Handler1),
    case catch Mod2:init({Args2, State2}) of
	{ok, State2a} ->
	    {ok, Handler#handler{state = State2a}};
	Other ->
	    report_terminate(Handler, crash, {error, Other}, SName, false),
	    no
    end.

new_handler({Mod,Id}, Handler1) ->
    {Mod, #handler{module = Mod,
		   id = Id,
		   supervised = Handler1#handler.supervised}};
new_handler(Mod, Handler1) ->
    {Mod, #handler{module = Mod,
		   supervised = Handler1#handler.supervised}}.


-spec split(handler(), [#handler{}]) ->
	{atom(), #handler{}, [#handler{}]} | 'error'.

split(Ha, MSL) -> split(Ha, MSL, []).

split({Mod,Id}, [Ha|T], L) when Ha#handler.module =:= Mod,
                                Ha#handler.id =:= Id ->
    {Mod, Ha, lists:reverse(L, T)};
split(Mod, [Ha|T], L) when Ha#handler.module =:= Mod,
                           not Ha#handler.id ->
    {Mod, Ha, lists:reverse(L, T)};
split(Ha, [H|T], L) ->
    split(Ha, T, [H|L]);
split(_, [], _) ->
    error.

%% server_call(Handler, Query, MSL, ServerName) ->
%%    {Reply, MSL1}

server_call(Handler, Query, MSL, SName) ->
    case search(Handler, MSL) of
	{ok, Ha} ->
	    case server_call_update(Ha, Query, SName) of
		{no, Reply} ->
		    {false, Reply, delete(Handler, MSL)};
		{{ok, Ha1}, Reply} ->
		    {false, Reply, replace(Handler, MSL, Ha1)};
		{{hibernate, Ha1}, Reply} ->
		    {true, Reply, replace(Handler, MSL, Ha1)}
	    end;
	false ->
	    {false, {error, bad_module}, MSL}
    end.

search({Mod, Id}, [Ha|_MSL]) when Ha#handler.module =:= Mod,
				  Ha#handler.id =:= Id ->
    {ok, Ha};
search(Mod, [Ha|_MSL]) when Ha#handler.module =:= Mod,
			    not Ha#handler.id ->
    {ok, Ha};
search(Handler, [_|MSL]) ->
    search(Handler, MSL);
search(_, []) ->
    false.

delete({Mod, Id}, [Ha|MSL]) when Ha#handler.module =:= Mod,
                                 Ha#handler.id =:= Id ->
    MSL;
delete(Mod, [Ha|MSL]) when Ha#handler.module =:= Mod,
                           not Ha#handler.id ->
    MSL;
delete(Handler, [Ha|MSL]) ->
    [Ha|delete(Handler, MSL)];
delete(_, []) ->
    [].

replace({Mod, Id}, [Ha|MSL], NewHa) when Ha#handler.module =:= Mod,
                                         Ha#handler.id =:= Id ->
    [NewHa|MSL];
replace(Mod, [Ha|MSL], NewHa) when Ha#handler.module =:= Mod,
                                   not Ha#handler.id ->
    [NewHa|MSL];
replace(Handler, [Ha|MSL], NewHa) ->
    [Ha|replace(Handler, MSL, NewHa)];
replace(_, [], NewHa) ->
    [NewHa].

%% server_call_update(Handler, Query, ServerName) ->
%%    {{Handler1, State1} | 'no', Reply}

server_call_update(Handler1, Query, SName) ->
    Mod1 = Handler1#handler.module,
    State = Handler1#handler.state,
    case catch Mod1:handle_call(Query, State) of
	{ok, Reply, State1} -> 
	    {{ok, Handler1#handler{state = State1}}, Reply};
	{ok, Reply, State1, hibernate} -> 
	    {{hibernate, Handler1#handler{state = State1}}, 
	     Reply};
	{swap_handler, Reply, Args1, State1, Handler2, Args2} ->
	    {do_swap(Mod1,Handler1,Args1,State1,Handler2,Args2,SName), Reply};
	{remove_handler, Reply} -> 
	    do_terminate(Mod1, Handler1, remove_handler, State,
			 remove, SName, normal),
	    {no, Reply};
	Other ->
	    do_terminate(Mod1, Handler1, {error, Other}, State,
			 Query, SName, crash),
	    {no, {error, Other}}
    end.

do_terminate(Mod, Handler, Args, State, LastIn, SName, Reason) ->
    Res = (catch Mod:terminate(Args, State)),
    report_terminate(Handler, Reason, Args, State, LastIn, SName, Res),
    Res.

report_terminate(Handler, crash, {error, Why}, State, LastIn, SName, _) ->
    report_terminate(Handler, Why, State, LastIn, SName);
report_terminate(Handler, How, _, State, LastIn, SName, _) ->
    %% How == normal | shutdown | {swapped, NewHandler, NewSupervisor}
    report_terminate(Handler, How, State, LastIn, SName).

report_terminate(Handler, Reason, State, LastIn, SName) ->
    report_error(Handler, Reason, State, LastIn, SName),
    case Handler#handler.supervised of
	false ->
	    ok;
	Pid ->
	    Pid ! {gen_event_EXIT,handler(Handler),Reason},
	    ok
    end.

report_error(_Handler, normal, _, _, _)             -> ok;
report_error(_Handler, shutdown, _, _, _)           -> ok;
report_error(_Handler, {swapped,_,_}, _, _, _)      -> ok;
report_error(Handler, Reason, State, LastIn, SName) ->
    Reason1 = 
	case Reason of
	    {'EXIT',{undef,[{M,F,A,L}|MFAs]}} ->
		case code:is_loaded(M) of
		    false ->
			{'module could not be loaded',[{M,F,A,L}|MFAs]};
		    _ ->
			case erlang:function_exported(M, F, length(A)) of
			    true ->
				{undef,[{M,F,A,L}|MFAs]};
			    false ->
				{'function not exported',[{M,F,A,L}|MFAs]}
			end
		end;
	    {'EXIT',Why} ->
		Why;
	    _ ->
		Reason
	end,
    Mod = Handler#handler.module,
    FmtState = case erlang:function_exported(Mod, format_status, 2) of
		   true ->
		       Args = [get(), State],
		       case catch Mod:format_status(terminate, Args) of
			   {'EXIT', _} -> State;
			   Else -> Else
		       end;
		   _ ->
		       State
	       end,
    error_msg("** gen_event handler ~p crashed.~n"
	      "** Was installed in ~p~n"
	      "** Last event was: ~p~n"
	      "** When handler state == ~p~n"
	      "** Reason == ~p~n",
	      [handler(Handler),SName,LastIn,FmtState,Reason1]).

handler(Handler) when not Handler#handler.id ->
    Handler#handler.module;
handler(Handler) ->
    {Handler#handler.module, Handler#handler.id}.

the_handlers(MSL) ->
    [handler(Handler) || Handler <- MSL].

%% stop_handlers(MSL, ServerName) -> []

stop_handlers([Handler|T], SName) ->
    Mod = Handler#handler.module,
    do_terminate(Mod, Handler, stop, Handler#handler.state,
		 stop, SName, shutdown),
    stop_handlers(T, SName);
stop_handlers([], _) ->
    [].

%% Message from the release_handler.
%% The list of modules got to be a set !
get_modules(MSL) ->
    Mods = [Handler#handler.module || Handler <- MSL],
    ordsets:to_list(ordsets:from_list(Mods)).

%%-----------------------------------------------------------------
%% Status information
%%-----------------------------------------------------------------
format_status(Opt, StatusData) ->
    [PDict, SysState, Parent, _Debug, [ServerName, MSL, _Hib]] = StatusData,
    Header = gen:format_status_header("Status for event handler",
                                      ServerName),
    FmtMSL = [case erlang:function_exported(Mod, format_status, 2) of
		  true ->
		      Args = [PDict, State],
		      case catch Mod:format_status(Opt, Args) of
			  {'EXIT', _} -> MSL;
			  Else -> MS#handler{state = Else}
		      end;
		  _ ->
		      MS
	      end || #handler{module = Mod, state = State} = MS <- MSL],
    [{header, Header},
     {data, [{"Status", SysState},
	     {"Parent", Parent}]},
     {items, {"Installed handlers", FmtMSL}}].