aboutsummaryrefslogtreecommitdiffstats
path: root/lib/stdlib/src/gen_statem.erl
blob: 6d7b461ee3d65943c2cd9ad912f626ade876bfec (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
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2016. 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(gen_statem).

%% API
-export(
   [start/3,start/4,start_link/3,start_link/4,
    stop/1,stop/3,
    cast/2,call/2,call/3,
    enter_loop/4,enter_loop/5,enter_loop/6,
    reply/1,reply/2]).

%% gen callbacks
-export(
   [init_it/6]).

%% sys callbacks
-export(
   [system_continue/3,
    system_terminate/4,
    system_code_change/4,
    system_get_state/1,
    system_replace_state/2,
    format_status/2]).

%% Internal callbacks
-export(
   [wakeup_from_hibernate/3]).

%% Type exports for templates
-export_type(
   [event_type/0,
    callback_mode/0,
    state_function_result/0,
    handle_event_result/0,
    action/0]).

%% Fix problem for doc build
-export_type([transition_option/0]).

%%%==========================================================================
%%% Interface functions.
%%%==========================================================================

-type from() ::
	{To :: pid(), Tag :: term()}. % Reply-to specifier for call

-type state() ::
	state_name() | % For StateName/3 callback functios
	term(). % For handle_event/4 callback function

-type state_name() :: atom().

-type data() :: term().

-type event_type() ::
	{'call',From :: from()} | 'cast' |
	'info' | 'timeout' | 'internal'.

-type callback_mode() :: 'state_functions' | 'handle_event_function'.

-type transition_option() ::
	postpone() | hibernate() | event_timeout().
-type postpone() ::
	%% If 'true' postpone the current event
	%% and retry it when the state changes (=/=)
	boolean().
-type hibernate() ::
	%% If 'true' hibernate the server instead of going into receive
	boolean().
-type event_timeout() ::
	%% Generate a ('timeout', EventContent, ...) event after Time
	%% unless some other event is delivered
	Time :: timeout().

-type action() ::
	%% During a state change:
	%% * NextState and NewData are set.
	%% * All action()s are executed in order of apperance.
	%% * Postponing the current event is performed
	%%   iff 'postpone' is 'true'.
	%% * A state timer is started iff 'timeout' is set.
	%% * Pending events are handled or if there are
	%%   no pending events the server goes into receive
	%%   or hibernate (iff 'hibernate' is 'true')
	%%
	%% These action()s are executed in order of appearence
	%% in the containing list. The ones that set options
	%% will override any previous so the last of each kind wins.
	%%
	'postpone' |  % Set the postpone option
	{'postpone', Postpone :: postpone()} |
	%%
	'hibernate' | % Set the hibernate option
	{'hibernate', Hibernate :: hibernate()} |
	%%
	(Timeout :: event_timeout()) | % {timeout,Timeout}
	{'timeout', % Set the event timeout option
	 Time :: event_timeout(), EventContent :: term()} |
	%%
	reply_action() |
	%%
	%% All 'next_event' events are kept in a list and then
	%% inserted at state changes so the first in the
	%% action() list is the first to be delivered.
	{'next_event', % Insert event as the next to handle
	 EventType :: event_type(),
	 EventContent :: term()}.
-type reply_action() ::
	{'reply', % Reply to a caller
	 From :: from(), Reply :: term()}.

-type state_function_result() ::
	{'next_state', % {next_state,NextStateName,NewData,[]}
	 NextStateName :: state_name(),
	 NewData :: data()} |
	{'next_state', % State transition, maybe to the same state
	 NextStateName :: state_name(),
	 NewData :: data(),
	 Actions :: [action()] | action()} |
	common_state_callback_result().
-type handle_event_result() ::
	{'next_state', % {next_state,NextState,NewData,[]}
	 NextState :: state(),
	 NewData :: data()} |
	{'next_state', % State transition, maybe to the same state
	 NextState :: state(),
	 NewData :: data(),
	 Actions :: [action()] | action()} |
	common_state_callback_result().
-type common_state_callback_result() ::
	'stop' | % {stop,normal}
	{'stop', % Stop the server
	 Reason :: term()} |
	{'stop', % Stop the server
	 Reason :: term(),
	 NewData :: data()} |
	{'stop_and_reply', % Reply then stop the server
	 Reason :: term(),
	 Replies :: [reply_action()] | reply_action()} |
	{'stop_and_reply', % Reply then stop the server
	 Reason :: term(),
	 Replies :: [reply_action()] | reply_action(),
	 NewData :: data()} |
	{'keep_state', % {keep_state,NewData,[]}
	 NewData :: data()} |
	{'keep_state', % Keep state, change data
	 NewData :: data(),
	 Actions :: [action()] | action()} |
	'keep_state_and_data' | % {keep_state_and_data,[]}
	{'keep_state_and_data', % Keep state and data -> only actions
	 Actions :: [action()] | action()}.


%% The state machine init function.  It is called only once and
%% the server is not running until this function has returned
%% an {ok, ...} tuple.  Thereafter the state callbacks are called
%% for all events to this server.
-callback init(Args :: term()) ->
    {ok, state(), data()} |
    {ok, state(), data(), [action()] | action()} |
    'ignore' |
    {'stop', Reason :: term()}.

%% This callback shall return the callback mode of the callback module.
%%
%% It is called once after init/0 and code_change/4 but before
%% the first state callback StateName/3 or handle_event/4.
-callback callback_mode() -> callback_mode().

%% Example state callback for StateName = 'state_name'
%% when callback_mode() =:= state_functions.
%%
%% In this mode all states has to be of type state_name() i.e atom().
%%
%% Note that the only callbacks that have arity 3 are these
%% StateName/3 callbacks and terminate/3, so the state name
%% 'terminate' is unusable in this mode.
-callback state_name(
	    event_type(),
	    EventContent :: term(),
	    Data :: data()) ->
    state_function_result().
%%
%% State callback for all states
%% when callback_mode() =:= handle_event_function.
-callback handle_event(
	    event_type(),
	    EventContent :: term(),
	    State :: state(), % Current state
	    Data :: data()) ->
    handle_event_result().

%% Clean up before the server terminates.
-callback terminate(
	    Reason :: 'normal' | 'shutdown' | {'shutdown', term()}
		    | term(),
	    State :: state(),
	    Data :: data()) ->
    any().

%% Note that the new code can expect to get an OldState from
%% the old code version not only in code_change/4 but in the first
%% state callback function called thereafter
-callback code_change(
	    OldVsn :: term() | {'down', term()},
	    OldState :: state(),
	    OldData :: data(),
	    Extra :: term()) ->
    {ok, NewState :: state(), NewData :: data()} |
    (Reason :: term()).

%% Format the callback module state in some sensible that is
%% often condensed way.  For StatusOption =:= 'normal' the perferred
%% return term is [{data,[{"State",FormattedState}]}], and for
%% StatusOption =:= 'terminate' it is just FormattedState.
-callback format_status(
	    StatusOption,
	    [ [{Key :: term(), Value :: term()}] |
	      state() |
	      data()]) ->
    Status :: term() when
      StatusOption :: 'normal' | 'terminate'.

-optional_callbacks(
   [init/1, % One may use enter_loop/5,6,7 instead
    format_status/2, % Has got a default implementation
    %%
    state_name/3, % Example for callback_mode() =:= state_functions:
    %% there has to be a StateName/3 callback function
    %% for every StateName in your state machine but the state name
    %% 'state_name' does of course not have to be used.
    %%
    handle_event/4 % For callback_mode() =:= handle_event_function
   ]).

%% Type validation functions
callback_mode(CallbackMode) ->
    case CallbackMode of
	state_functions ->
	    true;
	handle_event_function ->
	    true;
	_ ->
	    false
    end.
%%
from({Pid,_}) when is_pid(Pid) ->
    true;
from(_) ->
    false.
%%
event_type({call,From}) ->
    from(From);
event_type(Type) ->
    case Type of
	cast ->
	    true;
	info ->
	    true;
	timeout ->
	    true;
	internal ->
	    true;
	_ ->
	    false
    end.



-define(
   STACKTRACE(),
   try throw(ok) catch _ -> erlang:get_stacktrace() end).

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

-type server_name() ::
      {'global', GlobalName :: term()}
      | {'via', RegMod :: module(), Name :: term()}
      | {'local', atom()}.
-type server_ref() ::
      pid()
      | (LocalName :: atom())
      | {Name :: atom(), Node :: atom()}
      | {'global', GlobalName :: term()}
      | {'via', RegMod :: module(), ViaName :: term()}.
-type debug_opt() ::
	{'debug',
	 Dbgs ::
	   ['trace' | 'log' | 'statistics' | 'debug'
	    | {'logfile', string()}]}.
-type start_opt() ::
	debug_opt()
      | {'timeout', Time :: timeout()}
      | {'spawn_opt', [proc_lib:spawn_option()]}.
-type start_ret() ::  {'ok', pid()} | 'ignore' | {'error', term()}.



%% Start a state machine
-spec start(
	Module :: module(), Args :: term(), Opts :: [start_opt()]) ->
		   start_ret().
start(Module, Args, Opts) ->
    gen:start(?MODULE, nolink, Module, Args, Opts).
%%
-spec start(
	ServerName :: server_name(),
	Module :: module(), Args :: term(), Opts :: [start_opt()]) ->
		   start_ret().
start(ServerName, Module, Args, Opts) ->
    gen:start(?MODULE, nolink, ServerName, Module, Args, Opts).

%% Start and link to a state machine
-spec start_link(
	Module :: module(), Args :: term(), Opts :: [start_opt()]) ->
		   start_ret().
start_link(Module, Args, Opts) ->
    gen:start(?MODULE, link, Module, Args, Opts).
%%
-spec start_link(
	ServerName :: server_name(),
	Module :: module(), Args :: term(), Opts :: [start_opt()]) ->
		   start_ret().
start_link(ServerName, Module, Args, Opts) ->
    gen:start(?MODULE, link, ServerName, Module, Args, Opts).

%% Stop a state machine
-spec stop(ServerRef :: server_ref()) -> ok.
stop(ServerRef) ->
    gen:stop(ServerRef).
%%
-spec stop(
	ServerRef :: server_ref(),
	Reason :: term(),
	Timeout :: timeout()) -> ok.
stop(ServerRef, Reason, Timeout) ->
    gen:stop(ServerRef, Reason, Timeout).

%% Send an event to a state machine that arrives with type 'event'
-spec cast(ServerRef :: server_ref(), Msg :: term()) -> ok.
cast({global,Name}, Msg) ->
    try	global:send(Name, wrap_cast(Msg)) of
	_ -> ok
    catch
	_:_ -> ok
    end;
cast({via,RegMod,Name}, Msg) ->
    try	RegMod:send(Name, wrap_cast(Msg)) of
	_ -> ok
    catch
	_:_ -> ok
    end;
cast({Name,Node} = ServerRef, Msg) when is_atom(Name), is_atom(Node) ->
    send(ServerRef, wrap_cast(Msg));
cast(ServerRef, Msg) when is_atom(ServerRef) ->
    send(ServerRef, wrap_cast(Msg));
cast(ServerRef, Msg) when is_pid(ServerRef) ->
    send(ServerRef, wrap_cast(Msg)).

%% Call a state machine (synchronous; a reply is expected) that
%% arrives with type {call,From}
-spec call(ServerRef :: server_ref(), Request :: term()) -> Reply :: term().
call(ServerRef, Request) ->
    call(ServerRef, Request, infinity).
%%
-spec call(
	ServerRef :: server_ref(),
	Request :: term(),
	Timeout :: timeout()) ->
		  Reply :: term().
call(ServerRef, Request, infinity) ->
    try gen:call(ServerRef, '$gen_call', Request, infinity) of
	{ok,Reply} ->
	    Reply
    catch
	Class:Reason ->
	    erlang:raise(
	      Class,
	      {Reason,{?MODULE,call,[ServerRef,Request,infinity]}},
	      erlang:get_stacktrace())
    end;
call(ServerRef, Request, Timeout) ->
    %% Call server through proxy process to dodge any late reply
    Ref = make_ref(),
    Self = self(),
    Pid = spawn(
	    fun () ->
		    Self !
			try gen:call(
			      ServerRef, '$gen_call', Request, Timeout) of
			    Result ->
				{Ref,Result}
			catch Class:Reason ->
				{Ref,Class,Reason,erlang:get_stacktrace()}
			end
	    end),
    Mref = monitor(process, Pid),
    receive
	{Ref,Result} ->
	    demonitor(Mref, [flush]),
	    case Result of
		{ok,Reply} ->
		    Reply
	    end;
	{Ref,Class,Reason,Stacktrace} ->
	    demonitor(Mref, [flush]),
	    erlang:raise(
	      Class,
	      {Reason,{?MODULE,call,[ServerRef,Request,Timeout]}},
	      Stacktrace);
	{'DOWN',Mref,_,_,Reason} ->
	    %% There is a theoretical possibility that the
	    %% proxy process gets killed between try--of and !
	    %% so this clause is in case of that
	    exit(Reason)
    end.

%% Reply from a state machine callback to whom awaits in call/2
-spec reply([reply_action()] | reply_action()) -> ok.
reply({reply,From,Reply}) ->
    reply(From, Reply);
reply(Replies) when is_list(Replies) ->
    replies(Replies).
%%
-spec reply(From :: from(), Reply :: term()) -> ok.
reply({To,Tag}, Reply) when is_pid(To) ->
    Msg = {Tag,Reply},
    try To ! Msg of
	_ ->
	    ok
    catch
	_:_ -> ok
    end.

%% Instead of starting the state machine through start/3,4
%% or start_link/3,4 turn the current process presumably
%% started by proc_lib into a state machine using
%% the same arguments as you would have returned from init/1
-spec enter_loop(
	Module :: module(), Opts :: [debug_opt()],
	State :: state(), Data :: data()) ->
			no_return().
enter_loop(Module, Opts, State, Data) ->
    enter_loop(Module, Opts, State, Data, self()).
%%
-spec enter_loop(
	Module :: module(), Opts :: [debug_opt()],
	State :: state(), Data :: data(),
	Server_or_Actions ::
	  server_name() | pid() | [action()]) ->
			no_return().
enter_loop(Module, Opts, State, Data, Server_or_Actions) ->
    if
	is_list(Server_or_Actions) ->
	    enter_loop(Module, Opts, State, Data, self(), Server_or_Actions);
	true ->
	    enter_loop(Module, Opts, State, Data, Server_or_Actions, [])
    end.
%%
-spec enter_loop(
	Module :: module(), Opts :: [debug_opt()],
	State :: state(), Data :: data(),
	Server :: server_name() | pid(),
	Actions :: [action()] | action()) ->
			no_return().
enter_loop(Module, Opts, State, Data, Server, Actions) ->
    is_atom(Module) orelse error({atom,Module}),
    Parent = gen:get_parent(),
    enter(Module, Opts, State, Data, Server, Actions, Parent).

%%---------------------------------------------------------------------------
%% API helpers

wrap_cast(Event) ->
    {'$gen_cast',Event}.

replies([{reply,From,Reply}|Replies]) ->
    reply(From, Reply),
    replies(Replies);
replies([]) ->
    ok.

%% Might actually not send the message in case of caught exception
send(Proc, Msg) ->
    try erlang:send(Proc, Msg, [noconnect]) of
	noconnect ->
	    _ = spawn(erlang, send, [Proc,Msg]),
	    ok;
	ok ->
	    ok
    catch
	_:_ ->
	    ok
    end.

%% Here the init_it/6 and enter_loop/5,6,7 functions converge
enter(Module, Opts, State, Data, Server, Actions, Parent) ->
    %% The values should already have been type checked
    Name = gen:get_proc_name(Server),
    Debug = gen:debug_options(Name, Opts),
    P = Events = [],
    Event = {internal,initial_state},
    %% We enforce {postpone,false} to ensure that
    %% our fake Event gets discarded, thought it might get logged
    NewActions =
	if
	    is_list(Actions) ->
		Actions ++ [{postpone,false}];
	    true ->
		[Actions,{postpone,false}]
	end,
    S =	#{
      callback_mode => undefined,
      module => Module,
      name => Name,
      %% All fields below will be replaced according to the arguments to
      %% loop_event_actions/10 when it finally loops back to loop/3
      state => State,
      data => Data,
      postponed => P,
      hibernate => false,
      timer => undefined},
    NewDebug = sys_debug(Debug, S, State, {enter,Event,State}),
    loop_event_actions(
      Parent, NewDebug, S, Events,
      State, Data, P, Event, State, NewActions).

%%%==========================================================================
%%%  gen callbacks

init_it(Starter, self, ServerRef, Module, Args, Opts) ->
    init_it(Starter, self(), ServerRef, Module, Args, Opts);
init_it(Starter, Parent, ServerRef, Module, Args, Opts) ->
    try Module:init(Args) of
	Result ->
	    init_result(Starter, Parent, ServerRef, Module, Result, Opts)
    catch
	Result ->
	    init_result(Starter, Parent, ServerRef, Module, Result, Opts);
	Class:Reason ->
	    gen:unregister_name(ServerRef),
	    proc_lib:init_ack(Starter, {error,Reason}),
	    erlang:raise(Class, Reason, erlang:get_stacktrace())
    end.

%%---------------------------------------------------------------------------
%% gen callbacks helpers

init_result(Starter, Parent, ServerRef, Module, Result, Opts) ->
    case Result of
	{ok,State,Data} ->
	    proc_lib:init_ack(Starter, {ok,self()}),
	    enter(Module, Opts, State, Data, ServerRef, [], Parent);
	{ok,State,Data,Actions} ->
	    proc_lib:init_ack(Starter, {ok,self()}),
	    enter(Module, Opts, State, Data, ServerRef, Actions, Parent);
	{stop,Reason} ->
	    gen:unregister_name(ServerRef),
	    proc_lib:init_ack(Starter, {error,Reason}),
	    exit(Reason);
	ignore ->
	    gen:unregister_name(ServerRef),
	    proc_lib:init_ack(Starter, ignore),
	    exit(normal);
	_ ->
	    Error = {bad_return_value,Result},
	    proc_lib:init_ack(Starter, {error,Error}),
	    exit(Error)
    end.

%%%==========================================================================
%%% sys callbacks

system_continue(Parent, Debug, S) ->
    loop(Parent, Debug, S).

system_terminate(
  Reason, _Parent, Debug,
  #{state := State, data := Data, postponed := P} = S) ->
    terminate(
      exit, Reason, ?STACKTRACE(),
      Debug, S, [], State, Data, P).

system_code_change(
  #{module := Module,
    state := State,
    data := Data} = S,
  _Mod, OldVsn, Extra) ->
    case
	try Module:code_change(OldVsn, State, Data, Extra)
	catch
	    Result -> Result
	end
    of
	{ok,NewState,NewData} ->
	    {ok,
	     S#{callback_mode := undefined,
		state := NewState,
		data := NewData}};
	{ok,_} = Error ->
	    error({case_clause,Error});
	Error ->
	    Error
    end.

system_get_state(#{state := State, data := Data}) ->
    {ok,{State,Data}}.

system_replace_state(
  StateFun,
  #{state := State,
    data := Data} = S) ->
    {NewState,NewData} = Result = StateFun({State,Data}),
    {ok,Result,S#{state := NewState, data := NewData}}.

format_status(
  Opt,
  [PDict,SysState,Parent,Debug,
   #{name := Name, postponed := P, state := State, data := Data} = S]) ->
    Header = gen:format_status_header("Status for state machine", Name),
    Log = sys:get_debug(log, Debug, []),
    [{header,Header},
     {data,
      [{"Status",SysState},
       {"Parent",Parent},
       {"Logged Events",Log},
       {"Postponed",P}]} |
     case format_status(Opt, PDict, S, State, Data) of
	 L when is_list(L) -> L;
	 T -> [T]
     end].

%%---------------------------------------------------------------------------
%% 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,Event}, {Name,_}) ->
    io:format(
      Dev, "*DBG* ~p received ~s~n",
      [Name,event_string(Event)]);
print_event(Dev, {out,Reply,{To,_Tag}}, {Name,_}) ->
    io:format(
      Dev, "*DBG* ~p sent ~p to ~p~n",
      [Name,Reply,To]);
print_event(Dev, {Tag,Event,NextState}, {Name,State}) ->
    StateString =
	case NextState of
	    State ->
		io_lib:format("~p", [State]);
	    _ ->
		io_lib:format("~p => ~p", [State,NextState])
	end,
    io:format(
      Dev, "*DBG* ~p ~w ~s in state ~s~n",
      [Name,Tag,event_string(Event),StateString]).

event_string(Event) ->
    case Event of
	{{call,{Pid,_Tag}},Request} ->
	    io_lib:format("call ~p from ~w", [Request,Pid]);
	{EventType,EventContent} ->
	    io_lib:format("~w ~p", [EventType,EventContent])
    end.

sys_debug(Debug, #{name := Name}, State, Entry) ->
    case Debug of
	[] ->
	    Debug;
	_ ->
	    sys:handle_debug(
	      Debug, fun print_event/3, {Name,State}, Entry)
    end.

%%%==========================================================================
%%% Internal callbacks

wakeup_from_hibernate(Parent, Debug, S) ->
    %% It is a new message that woke us up so we have to receive it now
    loop_receive(Parent, Debug, S).

%%%==========================================================================
%%% State Machine engine implementation of proc_lib/gen server

%% Server loop, consists of all loop* functions
%% and detours through sys:handle_system_message/7 and proc_lib:hibernate/3

%% Entry point for system_continue/3
loop(Parent, Debug, #{hibernate := Hibernate} = S) ->
    case Hibernate of
	true ->
	    %% Does not return but restarts process at
	    %% wakeup_from_hibernate/3 that jumps to loop_receive/3
	    proc_lib:hibernate(
	      ?MODULE, wakeup_from_hibernate, [Parent,Debug,S]),
	    error(
	      {should_not_have_arrived_here_but_instead_in,
	       {wakeup_from_hibernate,3}});
	false ->
	    loop_receive(Parent, Debug, S)
    end.

%% Entry point for wakeup_from_hibernate/3
loop_receive(Parent, Debug, #{timer := Timer} = S) ->
    receive
	Msg ->
	    case Msg of
		{system,Pid,Req} ->
		    #{hibernate := Hibernate} = S,
		    %% Does not return but tail recursively calls
		    %% system_continue/3 that jumps to loop/3
		    sys:handle_system_msg(
		      Req, Pid, Parent, ?MODULE, Debug, S, Hibernate);
		{'EXIT',Parent,Reason} = EXIT ->
		    #{state := State, data := Data, postponed := P} = S,
		    %% EXIT is not a 2-tuple and therefore
		    %% not an event and has no event_type(),
		    %% but this will stand out in the crash report...
		    terminate(
		      exit, Reason, ?STACKTRACE(),
		      Debug, S, [EXIT], State, Data, P);
		{timeout,Timer,Content} when Timer =/= undefined ->
		    loop_receive_result(
		      Parent, Debug, S, {timeout,Content});
		_ ->
		    %% Cancel Timer if running
		    case Timer of
			undefined ->
			    ok;
			_ ->
			    case erlang:cancel_timer(Timer) of
				TimeLeft when is_integer(TimeLeft) ->
				    ok;
				false ->
				    receive
					{timeout,Timer,_} ->
					    ok
				    after 0 ->
					    ok
				    end
			    end
		    end,
		    Event =
			case Msg of
			    {'$gen_call',From,Request} ->
				{{call,From},Request};
			    {'$gen_cast',E} ->
				{cast,E};
			    _ ->
				{info,Msg}
			end,
		    loop_receive_result(Parent, Debug, S, Event)
	    end
    end.

loop_receive_result(
  Parent, Debug,
  #{state := State,
    data := Data,
    postponed := P} = S,
  Event) ->
    %% The engine state map S is now dismantled
    %% and will not be restored until we return to loop/3.
    %%
    %% The fields 'callback_mode', 'module', and 'name' are still valid.
    %% The fields 'state', 'data', and 'postponed' are held in arguments.
    %% The fields 'timer' and 'hibernate' will be recalculated.
    %%
    NewDebug = sys_debug(Debug, S, State, {in,Event}),
    %% Here the queue of not yet handled events is created
    Events = [],
    Hibernate = false,
    loop_event(
      Parent, NewDebug, S, Events, State, Data, P, Event, Hibernate).

%% Process the event queue, or if it is empty
%% loop back to loop/3 to receive a new event
loop_events(
  Parent, Debug, S, [Event|Events],
  State, Data, P, Hibernate, _Timeout) ->
    %%
    %% If there was a state timer requested we just ignore that
    %% since we have events to handle which cancels the timer
    loop_event(
      Parent, Debug, S, Events, State, Data, P, Event, Hibernate);
loop_events(
  Parent, Debug, S, [],
  State, Data, P, Hibernate, Timeout) ->
    case Timeout of
	{timeout,0,EventContent} ->
	    %% Immediate timeout - simulate it
	    %% so we do not get the timeout message
	    %% after any received event
	    loop_event(
	      Parent, Debug, S, [],
	      State, Data, P, {timeout,EventContent}, Hibernate);
	{timeout,Time,EventContent} ->
	    %% Actually start a timer
	    Timer = erlang:start_timer(Time, self(), EventContent),
	    loop_events_done(
	      Parent, Debug, S, Timer, State, Data, P, Hibernate);
	undefined ->
	    %% No state timeout has been requested
	    Timer = undefined,
	    loop_events_done(
	      Parent, Debug, S, Timer, State, Data, P, Hibernate)
    end.
%%
loop_events_done(Parent, Debug, S, Timer, State, Data, P, Hibernate) ->
    NewS =
	S#{
	  state := State,
	  data := Data,
	  postponed := P,
	  hibernate := Hibernate,
	  timer := Timer},
    loop(Parent, Debug, NewS).

loop_event(
  Parent, Debug,
  #{callback_mode := undefined,
    module := Module} = S,
  Events,
  State, Data, P, Event, Hibernate) ->
    %% Cache the callback_mode() value
    case
	try Module:callback_mode()
	catch
	    Result -> Result
	end
    of
	CallbackMode ->
	    case callback_mode(CallbackMode) of
		true ->
		    loop_event(
		      Parent, Debug,
		      S#{callback_mode := CallbackMode},
		      Events,
		      State, Data, P, Event, Hibernate);
		false ->
		    error({callback_mode,CallbackMode})
	    end
    end;
loop_event(
  Parent, Debug,
  #{callback_mode := CallbackMode,
    module := Module} = S,
  Events,
  State, Data, P, {Type,Content} = Event, Hibernate) ->
    %%
    %% If Hibernate is true here it can only be
    %% because it was set from an event action
    %% and we did not go into hibernation since there
    %% were events in queue, so we do what the user
    %% might depend on i.e collect garbage which
    %% would have happened if we actually hibernated
    %% and immediately was awakened
    Hibernate andalso garbage_collect(),
    %%
    try
	case CallbackMode of
	    state_functions ->
		Module:State(Type, Content, Data);
	    handle_event_function ->
		Module:handle_event(Type, Content, State, Data)
	end of
	Result ->
	    loop_event_result(
	      Parent, Debug, S, Events, State, Data, P, Event, Result)
    catch
	Result ->
	    loop_event_result(
	      Parent, Debug, S, Events, State, Data, P, Event, Result);
	error:badarg when CallbackMode =:= state_functions ->
	    case erlang:get_stacktrace() of
		[{erlang,apply,[Module,State,_],_}|Stacktrace] ->
		    Args = [Type,Content,Data],
		    terminate(
		      error,
		      {undef_state_function,{Module,State,Args}},
		      Stacktrace,
		      Debug, S, [Event|Events], State, Data, P);
		Stacktrace ->
		    terminate(
		      error, badarg, Stacktrace,
		      Debug, S, [Event|Events], State, Data, P)
	    end;
	error:undef ->
	    %% Process an undef to check for the simple mistake
	    %% of calling a nonexistent state function
	    case erlang:get_stacktrace() of
		[{Module,State,
		  [Type,Content,Data]=Args,
		  _}
		 |Stacktrace]
		when CallbackMode =:= state_functions ->
		    terminate(
		      error,
		      {undef_state_function,{Module,State,Args}},
		      Stacktrace,
		      Debug, S, [Event|Events], State, Data, P);
		[{Module,handle_event,
		  [Type,Content,State,Data]=Args,
		  _}
		 |Stacktrace]
		when CallbackMode =:= handle_event_function ->
		    terminate(
		      error,
		      {undef_state_function,{Module,handle_event,Args}},
		      Stacktrace,
		      Debug, S, [Event|Events], State, Data, P);
		Stacktrace ->
		    terminate(
		      error, undef, Stacktrace,
		      Debug, S, [Event|Events], State, Data, P)
	    end;
	Class:Reason ->
	    Stacktrace = erlang:get_stacktrace(),
	    terminate(
	      Class, Reason, Stacktrace,
	      Debug, S, [Event|Events], State, Data, P)
    end.

%% Interpret all callback return variants
loop_event_result(
  Parent, Debug, S, Events, State, Data, P, Event, Result) ->
    case Result of
	stop ->
	    terminate(
	      exit, normal, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, Data, P);
	{stop,Reason} ->
	    terminate(
	      exit, Reason, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, Data, P);
	{stop,Reason,NewData} ->
	    terminate(
	      exit, Reason, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, NewData, P);
	{stop_and_reply,Reason,Replies} ->
	    Q = [Event|Events],
	    reply_then_terminate(
	      exit, Reason, ?STACKTRACE(),
	      Debug, S, Q, State, Data, P, Replies);
	{stop_and_reply,Reason,Replies,NewData} ->
	    Q = [Event|Events],
	    reply_then_terminate(
	      exit, Reason, ?STACKTRACE(),
	      Debug, S, Q, State, NewData, P, Replies);
	{next_state,NextState,NewData} ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, []);
	{next_state,NextState,NewData,Actions} ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions);
	{keep_state,NewData} ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, State, []);
	{keep_state,NewData,Actions} ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, State, Actions);
	keep_state_and_data ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, Data, P, Event, State, []);
	{keep_state_and_data,Actions} ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, Data, P, Event, State, Actions);
	_ ->
	    terminate(
	      error, {bad_return_value,Result}, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, Data, P)
    end.

loop_event_actions(
  Parent, Debug, S, Events, State, NewData, P, Event, NextState, Actions) ->
    Postpone = false, % Shall we postpone this event; boolean()
    Hibernate = false,
    Timeout = undefined,
    NextEvents = [],
    loop_event_actions(
      Parent, Debug, S, Events, State, NewData, P, Event, NextState,
      if
	  is_list(Actions) ->
	      Actions;
	  true ->
	      [Actions]
      end,
      Postpone, Hibernate, Timeout, NextEvents).
%%
%% Process all actions
loop_event_actions(
  Parent, Debug, S, Events,
  State, NewData, P, Event, NextState, [Action|Actions],
  Postpone, Hibernate, Timeout, NextEvents) ->
    case Action of
	%% Actual actions
	{reply,From,Reply} ->
	    case from(From) of
		true ->
		    NewDebug = do_reply(Debug, S, State, From, Reply),
		    loop_event_actions(
		      Parent, NewDebug, S, Events,
		      State, NewData, P, Event, NextState, Actions,
		      Postpone, Hibernate, Timeout, NextEvents);
		false ->
		    terminate(
		      error, {bad_action,Action}, ?STACKTRACE(),
		      Debug, S, [Event|Events], State, NewData, P)
	    end;
	{next_event,Type,Content} ->
	    case event_type(Type) of
		true ->
		    loop_event_actions(
		      Parent, Debug, S, Events,
		      State, NewData, P, Event, NextState, Actions,
		      Postpone, Hibernate, Timeout,
		      [{Type,Content}|NextEvents]);
		false ->
		    terminate(
		      error, {bad_action,Action}, ?STACKTRACE(),
		      Debug, S, [Event|Events], State, NewData, P)
	    end;
	%% Actions that set options
	{postpone,NewPostpone} when is_boolean(NewPostpone) ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      NewPostpone, Hibernate, Timeout, NextEvents);
	{postpone,_} ->
	    terminate(
	      error, {bad_action,Action}, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, NewData, P);
	postpone ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      true, Hibernate, Timeout, NextEvents);
	{hibernate,NewHibernate} when is_boolean(NewHibernate) ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, NewHibernate, Timeout, NextEvents);
	{hibernate,_} ->
	    terminate(
	      error, {bad_action,Action}, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, NewData, P);
	hibernate ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, true, Timeout, NextEvents);
	{timeout,infinity,_} -> % Clear timer - it will never trigger
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, Hibernate, undefined, NextEvents);
	{timeout,Time,_} = NewTimeout when is_integer(Time), Time >= 0 ->
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, Hibernate, NewTimeout, NextEvents);
	{timeout,_,_} ->
	    terminate(
	      error, {bad_action,Action}, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, NewData, P);
	infinity -> % Clear timer - it will never trigger
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, Hibernate, undefined, NextEvents);
	Time when is_integer(Time), Time >= 0 ->
	    NewTimeout = {timeout,Time,Time},
	    loop_event_actions(
	      Parent, Debug, S, Events,
	      State, NewData, P, Event, NextState, Actions,
	      Postpone, Hibernate, NewTimeout, NextEvents);
	_ ->
	    terminate(
	      error, {bad_action,Action}, ?STACKTRACE(),
	      Debug, S, [Event|Events], State, NewData, P)
    end;
%%
%% End of actions list
loop_event_actions(
  Parent, Debug, S, Events,
  State, NewData, P0, Event, NextState, [],
  Postpone, Hibernate, Timeout, NextEvents) ->
    %%
    %% All options have been collected and next_events are buffered.
    %% Do the actual state transition.
    %%
    P1 = % Move current event to postponed if Postpone
	case Postpone of
	    true ->
		[Event|P0];
	    false ->
		P0
	end,
    {Q2,P} = % Move all postponed events to queue if state change
	if
	    NextState =:= State ->
		{Events,P1};
	    true ->
		{lists:reverse(P1, Events),[]}
	end,
    %% Place next events first in queue
    Q = lists:reverse(NextEvents, Q2),
    %%
    NewDebug =
	sys_debug(
	  Debug, S, State,
	  case Postpone of
	      true ->
		  {postpone,Event,NextState};
	      false ->
		  {consume,Event,NextState}
	  end),
    loop_events(
      Parent, NewDebug, S, Q, NextState, NewData, P, Hibernate, Timeout).

%%---------------------------------------------------------------------------
%% Server helpers

reply_then_terminate(
  Class, Reason, Stacktrace,
  Debug, S, Q, State, Data, P, Replies) ->
    if
	is_list(Replies) ->
	    do_reply_then_terminate(
	      Class, Reason, Stacktrace,
	      Debug, S, Q, State, Data, P, Replies);
	true ->
	    do_reply_then_terminate(
	      Class, Reason, Stacktrace,
	      Debug, S, Q, State, Data, P, [Replies])
    end.
%%
do_reply_then_terminate(
  Class, Reason, Stacktrace, Debug, S, Q, State, Data, P, []) ->
    terminate(Class, Reason, Stacktrace, Debug, S, Q, State, Data, P);
do_reply_then_terminate(
  Class, Reason, Stacktrace, Debug, S, Q, State, Data, P, [R|Rs]) ->
    case R of
	{reply,{_To,_Tag}=From,Reply} ->
	    NewDebug = do_reply(Debug, S, State, From, Reply),
	    do_reply_then_terminate(
	      Class, Reason, Stacktrace,
	      NewDebug, S, Q, State, Data, P, Rs);
	_ ->
	    terminate(
	      error, {bad_action,R}, ?STACKTRACE(),
	      Debug, S, Q, State, Data, P)
    end.

do_reply(Debug, S, State, From, Reply) ->
    reply(From, Reply),
    sys_debug(Debug, S, State, {out,Reply,From}).


terminate(
  Class, Reason, Stacktrace,
  Debug, #{module := Module} = S, Q, State, Data, P) ->
    try Module:terminate(Reason, State, Data) of
	_ -> ok
    catch
	_ -> ok;
	C:R ->
	    ST = erlang:get_stacktrace(),
	    error_info(
	      C, R, ST, Debug, S, Q, P,
	      format_status(terminate, get(), S, State, Data)),
	    erlang:raise(C, R, ST)
    end,
    case Reason of
	normal -> ok;
	shutdown -> ok;
	{shutdown,_} -> ok;
	_ ->
	    error_info(
	      Class, Reason, Stacktrace, Debug, S, Q, P,
	      format_status(terminate, get(), S, State, Data))
    end,
    case Stacktrace of
	[] ->
	    erlang:Class(Reason);
	_ ->
	    erlang:raise(Class, Reason, Stacktrace)
    end.

error_info(
  Class, Reason, Stacktrace, Debug,
  #{name := Name, callback_mode := CallbackMode},
  Q, P, FmtData) ->
    {FixedReason,FixedStacktrace} =
	case Stacktrace of
	    [{M,F,Args,_}|ST]
	      when Class =:= error, Reason =:= undef ->
		case code:is_loaded(M) of
		    false ->
			{{'module could not be loaded',M},ST};
		    _ ->
			Arity =
			    if
				is_list(Args) ->
				    length(Args);
				is_integer(Args) ->
				    Args
			    end,
			case erlang:function_exported(M, F, Arity) of
			    true ->
				{Reason,Stacktrace};
			    false ->
				{{'function not exported',{M,F,Arity}},
				 ST}
			end
		end;
	    _ -> {Reason,Stacktrace}
	end,
    error_logger:format(
      "** State machine ~p terminating~n" ++
	  case Q of
	      [] -> "";
	      _ -> "** Last event = ~p~n"
	  end ++
	  "** When server state  = ~p~n" ++
	  "** Reason for termination = ~w:~p~n" ++
	  "** Callback mode = ~p~n" ++
	  case Q of
	      [_,_|_] -> "** Queued = ~p~n";
	      _ -> ""
	  end ++
	  case P of
	      [] -> "";
	      _ -> "** Postponed = ~p~n"
	  end ++
	  case FixedStacktrace of
	      [] -> "";
	      _ -> "** Stacktrace =~n**  ~p~n"
	  end,
      [Name |
       case Q of
	   [] -> [];
	   [Event|_] -> [Event]
       end] ++
	  [FmtData,Class,FixedReason,
	   CallbackMode] ++
	  case Q of
	      [_|[_|_] = Events] -> [Events];
	      _ -> []
	  end ++
	  case P of
	      [] -> [];
	      _ -> [P]
	  end ++
	  case FixedStacktrace of
	      [] -> [];
	      _ -> [FixedStacktrace]
	  end),
    sys:print_log(Debug),
    ok.


%% Call Module:format_status/2 or return a default value
format_status(Opt, PDict, #{module := Module}, State, Data) ->
    case erlang:function_exported(Module, format_status, 2) of
	true ->
	    try Module:format_status(Opt, [PDict,State,Data])
	    catch
		Result -> Result;
		_:_ ->
		    format_status_default(
		      Opt, State,
		      "Module:format_status/2 crashed")
	    end;
	false ->
	    format_status_default(Opt, State, Data)
    end.

%% The default Module:format_status/2
format_status_default(Opt, State, Data) ->
    SSD = {State,Data},
    case Opt of
	terminate ->
	    SSD;
	_ ->
	    [{data,[{"State",SSD}]}]
    end.