aboutsummaryrefslogblamecommitdiffstats
path: root/lib/sasl/src/release_handler_1.erl
blob: 9c0edf4e9917f83217ef6cae6130f3ae9a00b83e (plain) (tree)
1
2
3
4
5
6
7
8
9
10
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
                   

                                                        



                                                                      
  


                                                                         
  


























































































































































































































































































































































































































































































































































                                                                                   





                                                                                
























































































                                                                                
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2010. 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(release_handler_1).

%% External exports
-export([eval_script/3, eval_script/4, check_script/2]).
-export([get_vsn/1]). %% exported because used in a test case

-record(eval_state, {bins = [], stopped = [], suspended = [], apps = [],
		     libdirs, unpurged = [], vsns = [], newlibs = [],
		     opts = []}).
%%-----------------------------------------------------------------
%% bins      = [{Mod, Binary, FileName}]
%% stopped   = [{Mod, [pid()]}] - list of stopped pids for each module
%% suspended = [{Mod, [pid()]}] - list of suspended pids for each module
%% apps      = [app_spec()] - list of all apps in the new release
%% libdirs   = [{Lib, LibVsn, LibDir}] - Maps Lib to Vsn and Directory
%% unpurged  = [{Mod, soft_purge | brutal_purge}]
%% vsns      = [{Mod, OldVsn, NewVsn}] - remember the old vsn of a mod
%%                  before it is removed/a new vsn is loaded; the new vsn
%%                  is kept in case of a downgrade, where the code_change
%%                  function receives the vsn of the module to downgrade
%%                  *to*.
%% newlibs   = [{Lib, Dir}] - list of all new libs; used to change
%%                            the code path
%% opts      = [{Tag, Value}] - list of options
%%-----------------------------------------------------------------


%%%-----------------------------------------------------------------
%%% This is a low-level release handler.
%%%-----------------------------------------------------------------
check_script(Script, LibDirs) ->
    case catch check_old_processes(Script) of
	ok ->
	    {Before, _After} = split_instructions(Script),
	    case catch lists:foldl(fun(Instruction, EvalState1) ->
					   eval(Instruction, EvalState1)
				   end,
				   #eval_state{libdirs = LibDirs},
				   Before) of
		EvalState2 when is_record(EvalState2, eval_state) -> ok;
		{error, Error} -> {error, Error};
		Other -> {error, Other}
	    end;
	{error, Mod} ->
	    {error, {old_processes, Mod}}
    end.

eval_script(Script, Apps, LibDirs) ->
    eval_script(Script, Apps, LibDirs, []).

eval_script(Script, Apps, LibDirs, Opts) ->
    case catch check_old_processes(Script) of
	ok ->
	    {Before, After} = split_instructions(Script),
	    case catch lists:foldl(fun(Instruction, EvalState1) ->
					   eval(Instruction, EvalState1)
				   end,
				   #eval_state{apps = Apps, 
					       libdirs = LibDirs,
					       opts = Opts},
				   Before) of
		EvalState2 when is_record(EvalState2, eval_state) ->
		    case catch lists:foldl(fun(Instruction, EvalState3) ->
						   eval(Instruction, EvalState3)
					   end,
					   EvalState2,
					   After) of
			EvalState4 when is_record(EvalState4, eval_state) ->
			    {ok, EvalState4#eval_state.unpurged};
			restart_new_emulator ->
			    restart_new_emulator;
			Error ->
			    {'EXIT', Error}
		    end;
		{error, Error} -> {error, Error};
		Other -> {error, Other}
	    end;
	{error, Mod} ->
	    {error, {old_processes, Mod}}
    end.

%%%-----------------------------------------------------------------
%%% Internal functions
%%%-----------------------------------------------------------------
split_instructions(Script) ->
    split_instructions(Script, []).
split_instructions([point_of_no_return | T], Before) ->
    {lists:reverse(Before), [point_of_no_return | T]};
split_instructions([H | T], Before) ->
    split_instructions(T, [H | Before]);
split_instructions([], Before) ->
    {[], lists:reverse(Before)}.

%%-----------------------------------------------------------------
%% Func: check_old_processes/1
%% Args: Script = [instruction()]
%% Purpose: Check if there is any process that runs an old version
%%          of a module that should be soft_purged, (i.e. not purged
%%          at all if there is any such process).  Returns {error, Mod}
%%          if so, ok otherwise.
%% Returns: ok | {error, Mod}
%%          Mod = atom()  
%%-----------------------------------------------------------------
check_old_processes(Script) ->
    lists:foreach(fun({load, {Mod, soft_purge, _PostPurgeMethod}}) ->
			  check_old_code(Mod);
		     ({remove, {Mod, soft_purge, _PostPurgeMethod}}) ->
			  check_old_code(Mod);
		     (_) -> ok
		  end,
		  Script).

check_old_code(Mod) ->
    lists:foreach(fun(Pid) ->
			  case erlang:check_process_code(Pid, Mod) of
			      false -> ok;
			      true -> throw({error, Mod})
			  end
		  end,
		  erlang:processes()).

%%-----------------------------------------------------------------
%% An unpurged module is a module for which there exist an old
%% version of the code.  This should only be the case if there are
%% processes running the old version of the code.
%%
%% This functions evaluates each instruction.  Note that the
%% instructions here are low-level instructions.  e.g. lelle's
%% old synchronized_change would be translated to
%%   {load_object_code, Modules},
%%   {suspend, Modules}, [{load, Module}],
%%   {resume, Modules}, {purge, Modules}
%% Or, for example, if we want to do advanced external code change 
%% on two modules that depend on each other, by killing them and
%% then restaring them, we could do:
%%   {load_object_code, [Mod1, Mod2]},
%%   % delete old version
%%   {remove, {Mod1, brutal_purge}}, {remove, {Mod2, brutal_purge}},
%%   % now, some procs migth be running prev current (now old) version
%%   % kill them, and load new version
%%   {load, {Mod1, brutal_purge}}, {load, {Mod2, brutal_purge}}
%%   % now, there is one version of the code (new, current)
%%
%% NOTE: All load_object_code must be first in the script,
%%       a point_of_no_return must be present (if load_object_code
%%       is present).
%%
%% {load_object_code, {Lib, LibVsn, [Mod]} 
%%    read the files as binarys. do not make code out of them
%% {load, {Module, PrePurgeMethod, PostPurgeMethod}}
%%    Module must have been load_object_code:ed.  make code out of it
%%    old procs && soft_purge => no new release
%%    old procs && brutal_purge => old procs killed
%%    The new old code will be gc:ed later on, if PostPurgeMethod =
%%    soft_purge.  If it is brutal_purge, the code is purged when
%%    the release is made permanent.
%% {remove, {Module, PrePurgeMethod, PostPurgeMethod}}
%%    make current version old.  no current left.
%%    old procs && soft_purge => no new release
%%    old procs && brutal_purge => old procs killed
%%    The new old code will be gc:ed later on, if PostPurgeMethod =
%%    soft_purge.  If it is brutal_purge, the code is purged when
%%    the release is made permanent.
%% {purge, Modules}
%%    kill all procs running old code, delete old code
%% {suspend, [Module | {Module, Timeout}]}
%%    If a process doesn't repsond - never mind.  It will be killed
%%    later on (if a purge is performed).
%%    Hmm, we must do something smart here... we should probably kill it,
%%    but we cant, because its supervisor will restart it directly!  Maybe
%%    we should keep a list of those, call supervisor:terminate_child()
%%    when all others are suspended, and call sup:restart_child() when the
%%    others are resumed.
%% {code_change, [{Module, Extra}]}
%% {code_change, Mode, [{Module, Extra}]}  Mode = up | down
%%    Send code_change only to suspended procs running this code
%% {resume, [Module]}
%%    resume all previously suspended processes
%% {stop, [Module]}
%%    stop all procs running this code
%% {start, [Module]}
%%    starts the procs that were previously stopped for this code.
%%    Note that this will start processes in exactly the same place
%%    in the suptree where there were procs previously.
%% {sync_nodes, Id, [Node]}
%% {sync_nodes, Id, {M, F, A}}
%%    Synchronizes with the Nodes (or apply(M,F,A) == Nodes).  All Nodes
%%    must also exectue the same line.  Waits for all these nodes to get
%%    to this line.
%% point_of_no_return
%% restart_new_emulator
%% {stop_application, Appl}     - Impl with apply
%% {unload_application, Appl}   - Impl with {remove..}
%% {load_application, Appl}     - Impl with {load..}
%% {start_application, Appl}    - Impl with apply
%%-----------------------------------------------------------------
eval({load_object_code, {Lib, LibVsn, Modules}}, EvalState) ->
    case lists:keysearch(Lib, 1, EvalState#eval_state.libdirs) of
	{value, {Lib, LibVsn, LibDir}} ->
	    Ebin = filename:join(LibDir, "ebin"),
	    Ext = code:objfile_extension(),
	    {NewBins, NewVsns} = 
		lists:foldl(fun(Mod, {Bins, Vsns}) ->
				    File = lists:concat([Mod, Ext]),
				    FName = filename:join(Ebin, File),
				    case erl_prim_loader:get_file(FName) of
					{ok, Bin, FName2} ->
					    NVsns = add_new_vsn(Mod, FName2, Vsns),
					    {[{Mod, Bin, FName2} | Bins],NVsns};
					error ->
					    throw({error, {no_such_file,FName}})
				    end
			    end,
			    {EvalState#eval_state.bins,
			     EvalState#eval_state.vsns},
			    Modules),
	    NewLibs = [{Lib, Ebin} | EvalState#eval_state.newlibs],
	    EvalState#eval_state{bins = NewBins,
				 newlibs = NewLibs,
				 vsns = NewVsns};
	{value, {Lib, LibVsn2, _LibDir}} ->
	    throw({error, {bad_lib_vsn, Lib, LibVsn2}})
    end;
eval(point_of_no_return, EvalState) ->
    Libs = case get_opt(update_paths, EvalState, false) of
	       false ->
		   EvalState#eval_state.newlibs; % [{Lib, Path}]
	       true ->
		   lists:map(fun({Lib, _LibVsn, LibDir}) ->
				     Ebin= filename:join(LibDir,"ebin"),
				     {Lib, Ebin}
			     end,
			     EvalState#eval_state.libdirs)
	   end,
    lists:foreach(fun({Lib, Path}) -> code:replace_path(Lib, Path) end,
		  Libs),
    EvalState;
eval({load, {Mod, _PrePurgeMethod, PostPurgeMethod}}, EvalState) ->
    Bins = EvalState#eval_state.bins,
    {value, {_Mod, Bin, File}} = lists:keysearch(Mod, 1, Bins),
    % load_binary kills all procs running old code
    % if soft_purge, we know that there are no such procs now
    Vsns = EvalState#eval_state.vsns,
    NewVsns = add_old_vsn(Mod, Vsns),
    code:load_binary(Mod, File, Bin),
    % Now, the prev current is old.  There might be procs
    % running it.  Find them.
    Unpurged = do_soft_purge(Mod,PostPurgeMethod,EvalState#eval_state.unpurged),
    EvalState#eval_state{bins = lists:keydelete(Mod, 1, Bins),
			 unpurged = Unpurged,
			 vsns = NewVsns};
eval({remove, {Mod, _PrePurgeMethod, PostPurgeMethod}}, EvalState) ->
    % purge kills all procs running old code
    % if soft_purge, we know that there are no such procs now
    Vsns = EvalState#eval_state.vsns,
    NewVsns = add_old_vsn(Mod, Vsns),
    code:purge(Mod),
    code:delete(Mod),
    % Now, the prev current is old.  There might be procs
    % running it.  Find them.
    Unpurged =
	case code:soft_purge(Mod) of
	    true -> EvalState#eval_state.unpurged;
	    false -> [{Mod, PostPurgeMethod} | EvalState#eval_state.unpurged]
	end,
%%    Bins = EvalState#eval_state.bins,
%%    EvalState#eval_state{bins = lists:keydelete(Mod, 1, Bins),
    EvalState#eval_state{unpurged = Unpurged, vsns = NewVsns};
eval({purge, Modules}, EvalState) ->
    % Now, if there are any processes still executing old code, OR
    % if some new processes started after suspend but before load,
    % these are killed.
    lists:foreach(fun(Mod) -> code:purge(Mod) end, Modules),
    EvalState;
eval({suspend, Modules}, EvalState) ->
    Procs = get_supervised_procs(),
    NewSuspended =
	lists:foldl(fun(ModSpec, Suspended) ->
			    {Module, Def} = case ModSpec of 
						{Mod, ModTimeout} ->
						    {Mod, ModTimeout};
						Mod ->
						    {Mod, default}
					    end,
			    Timeout = get_opt(suspend_timeout, EvalState, Def),
			    Pids = suspend(Module, Procs, Timeout),
			    [{Module, Pids} | Suspended]
		    end,
		    EvalState#eval_state.suspended,
		    Modules),
    EvalState#eval_state{suspended = NewSuspended};
eval({resume, Modules}, EvalState) ->
    NewSuspended =
	lists:foldl(fun(Mod, Suspended) ->
			    lists:filter(fun({Mod2, Pids}) when Mod2 == Mod ->
						 resume(Pids),
						 false;
					    (_) ->
						 true
					 end,
					 Suspended)
		    end,
		    EvalState#eval_state.suspended,
		    Modules),
    EvalState#eval_state{suspended = NewSuspended};
eval({code_change, Modules}, EvalState) ->
    eval({code_change, up, Modules}, EvalState);
eval({code_change, Mode, Modules}, EvalState) ->
    Suspended = EvalState#eval_state.suspended,
    Vsns = EvalState#eval_state.vsns,
    Timeout = get_opt(code_change_timeout, EvalState, default),
    lists:foreach(fun({Mod, Extra}) ->
			  Vsn =
			      case lists:keysearch(Mod, 1, Vsns) of
				  {value, {Mod, OldVsn, _NewVsn}}
				    when Mode == up -> OldVsn;
				  {value, {Mod, _OldVsn, NewVsn}}
				    when Mode == down -> {down, NewVsn};
				  _ when Mode == up -> undefined;
				  _ -> {down, undefined}
			      end,
			  case lists:keysearch(Mod, 1, Suspended) of
			      {value, {_Mod, Pids}} ->
				  change_code(Pids, Mod, Vsn, Extra, Timeout);
			      _ -> ok
			  end
		  end,
		  Modules),
    EvalState;
eval({stop, Modules}, EvalState) ->
    Procs = get_supervised_procs(),
    NewStopped =
	lists:foldl(fun(Mod, Stopped) ->
			    Procs2 = stop(Mod, Procs),
			    [{Mod, Procs2} | Stopped]
		    end,
		    EvalState#eval_state.stopped,
		    Modules),
    EvalState#eval_state{stopped = NewStopped};
eval({start, Modules}, EvalState) ->
    NewStopped =
	lists:foldl(fun(Mod, Stopped) ->
			    lists:filter(fun({Mod2, Procs}) when Mod2 == Mod ->
						 start(Procs),
						 false;
					    (_) ->
						 true
					 end,
					 Stopped)
		    end,
		    EvalState#eval_state.stopped,
		    Modules),
    EvalState#eval_state{stopped = NewStopped};
eval({sync_nodes, Id, {M, F, A}}, EvalState) ->
    sync_nodes(Id, apply(M, F, A)),
    EvalState;
eval({sync_nodes, Id, Nodes}, EvalState) ->
    sync_nodes(Id, Nodes),
    EvalState;
eval({apply, {M, F, A}}, EvalState) ->
    apply(M, F, A),
    EvalState;
eval(restart_new_emulator, _EvalState) ->
    throw(restart_new_emulator).

get_opt(Tag, EvalState, Default) ->
    case lists:keysearch(Tag, 1, EvalState#eval_state.opts) of
	{value,  {_Tag, Value}} -> Value;
	false                   -> Default
    end.

%%-----------------------------------------------------------------
%% This is a first approximation.  Unfortunately, we might end up
%% with the situation that after this suspendation, some new
%% processes start *before* we have loaded the new code, and these
%% will execute the old code.  These processes could be terminated
%% later on (if the prev current version is purged).  The same
%% goes for processes that didn't respond to the suspend message.
%%-----------------------------------------------------------------
suspend(Mod, Procs, Timeout) ->
    lists:zf(fun({_Sup, _Name, Pid, Mods}) -> 
		     case lists:member(Mod, Mods) of
			 true ->
			     case catch sys_suspend(Pid, Timeout) of
				 ok -> {true, Pid};
				 _ -> 
				     % If the proc hangs, make sure to
				     % resume it when it gets suspended!
				     catch sys:resume(Pid),
				     false
			     end;
			 false ->
			     false
		     end
	     end,
	     Procs).

sys_suspend(Pid, default) ->
    sys:suspend(Pid);
sys_suspend(Pid, Timeout) ->
    sys:suspend(Pid, Timeout).

resume(Pids) ->
    lists:foreach(fun(Pid) -> catch sys:resume(Pid) end, Pids).

change_code(Pids, Mod, Vsn, Extra, Timeout) ->
    Fun = fun(Pid) -> 
		  case Timeout of
		      default ->
			  ok = sys:change_code(Pid, Mod, Vsn, Extra);
		      _Else ->
			  ok = sys:change_code(Pid, Mod, Vsn, Extra, Timeout)
		  end
	  end,
    lists:foreach(Fun, Pids).

stop(Mod, Procs) ->
    lists:zf(fun({undefined, _Name, _Pid, _Mods}) ->
		     false;
		({Sup, Name, _Pid, Mods}) -> 
		     case lists:member(Mod, Mods) of
			 true ->
			     case catch supervisor:terminate_child(
					  Sup, Name) of
				 ok -> {true, {Sup, Name}};
				 _ -> false
			     end;
			 false -> false
		     end
	     end,
	     Procs).

start(Procs) ->
    lists:foreach(fun({Sup, Name}) -> 
			  catch supervisor:restart_child(Sup, Name)
		  end,
		  Procs).

%%-----------------------------------------------------------------
%% Func: get_supervised_procs/0
%% Purpose: This is the magic function.  It finds all process in
%%          the system and which modules they execute as a call_back or
%%          process module.
%%          This is achieved by asking the main supervisor for the
%%          applications for all children and their modules
%%          (recursively).
%% NOTE: If a supervisor is suspended, it isn't possible to call
%%       which_children.  Code change on a supervisor should be
%%       done in another way; the only code in a supervisor is
%%       code for starting children.  Therefore, to change a
%%       supervisor module, we should load the new version, and then
%%       delete the old.  Then we should perform the start changes
%%       manually, by adding/deleting children.
%% Returns: [{SuperPid, ChildName, ChildPid, Mods}]
%%-----------------------------------------------------------------
%% OTP-3452. For each application the first item contains the pid
%% of the top supervisor, and the name of the supervisor call-back module.  
%%-----------------------------------------------------------------

get_supervised_procs() ->
    lists:foldl(
      fun(Application, Procs) ->
	      case application_controller:get_master(Application) of
		  Pid when is_pid(Pid) ->
		      {Root, _AppMod} = application_master:get_child(Pid),
		      case get_supervisor_module(Root) of
			  {ok, SupMod} ->
			      get_procs(supervisor:which_children(Root), 
					Root) ++
				  [{undefined, undefined, Root, [SupMod]} | 
				   Procs];
			  {error, _} ->
			      error_logger:error_msg("release_handler: "
						     "cannot find top "
						     "supervisor for "
						    "application ~w~n", 
						    [Application]),
			      get_procs(supervisor:which_children(Root), 
					Root) ++ Procs
		      end;
		  _ -> Procs
	      end
      end,
      [],
      lists:map(fun({Application, _Name, _Vsn}) ->
			Application
		end,
		application:which_applications())).

get_procs([{Name, Pid, worker, dynamic} | T], Sup) when is_pid(Pid) ->
    Mods = get_dynamic_mods(Pid),
    [{Sup, Name, Pid, Mods} | get_procs(T, Sup)];
get_procs([{Name, Pid, worker, Mods} | T], Sup) when is_pid(Pid), is_list(Mods) ->
    [{Sup, Name, Pid, Mods} | get_procs(T, Sup)];
get_procs([{Name, Pid, supervisor, Mods} | T], Sup) when is_pid(Pid) ->
    [{Sup, Name, Pid, Mods} | get_procs(T, Sup)] ++ 
	get_procs(supervisor:which_children(Pid), Pid);
get_procs([_H | T], Sup) ->
    get_procs(T, Sup);
get_procs(_, _Sup) ->
    [].

get_dynamic_mods(Pid) ->
    {ok,Res} = gen:call(Pid, self(), get_modules),
    Res.

%% XXXX
%% Note: The following is a terrible hack done in order to resolve the
%% problem stated in ticket OTP-3452.

%% XXXX NOTE WELL: This record is from supervisor.erl. Also the record
%% name is really `state'. 
-record(supervisor_state, {name,
                strategy,
                children = [],
                dynamics = [],
                intensity,
                period,
                restarts = [],
                module,
                args}).

%% Return the name of the call-back module that implements the
%% (top) supervisor SupPid.
%% Returns: {ok, Module} | {error,undefined}
%%
get_supervisor_module(SupPid) ->
    case catch get_supervisor_module1(SupPid) of
	{ok, Module} when is_atom(Module) ->
	    {ok, Module};
	_Other ->
	    io:format("~w: reason: ~w~n", [SupPid, _Other]),
	    {error, undefined}
    end.

get_supervisor_module1(SupPid) ->
    {status, _Pid, {module, _Mod}, 
     [_PDict, _SysState, _Parent, _Dbg, Misc]} = sys:get_status(SupPid),
    %% supervisor Misc field changed at R13B04, handle old and new variants here
    State = case Misc of
                [_Name, State1, _Type, _Time] ->
                    State1;
                [_Header, _Data, {data, [{"State", State2}]}] ->
                    State2
            end,
    %% Cannot use #supervisor_state{module = Module} = State.
    {ok, element(#supervisor_state.module, State)}.

%%-----------------------------------------------------------------
%% Func: do_soft_purge/3
%% Args: Mod = atom()
%%       PostPurgeMethod = soft_purge | brutal_purge
%%       Unpurged = [{Mod, PostPurgeMethod}]
%% Purpose: Check if there are any processes left running this code.
%%          If so, make sure Mod is a member in the returned list.
%%          Otherwise, make sure Mod isn't a member in the returned
%%          list.
%% Returns: An updated list of unpurged modules.
%%-----------------------------------------------------------------
do_soft_purge(Mod, PostPurgeMethod, Unpurged) ->
    IsNoOldProcsLeft = code:soft_purge(Mod),
    case lists:keymember(Mod, 1, Unpurged) of
	true when IsNoOldProcsLeft == true -> lists:keydelete(Mod, 1, Unpurged);
	true -> Unpurged;
	false when IsNoOldProcsLeft == true -> Unpurged;
	false -> [{Mod, PostPurgeMethod} | Unpurged]
    end.

%%-----------------------------------------------------------------
%% Func: sync_nodes/2
%% Args: Id = term()
%%       Nodes = [atom()]
%% Purpose: Synchronizes with all nodes.
%%-----------------------------------------------------------------
sync_nodes(Id, Nodes) ->
    NNodes = lists:delete(node(), Nodes),
    lists:foreach(fun(Node) ->
			  {release_handler, Node} ! {sync_nodes, Id, node()}
		  end,
		  NNodes),
    lists:foreach(fun(Node) ->
			  receive
			      {sync_nodes, Id, Node} ->
				  ok;
			      {nodedown, Node} ->
				  throw({sync_error, {nodedown, Node}})
			  end
		  end,
		  NNodes).

add_old_vsn(Mod, Vsns) ->
    case lists:keysearch(Mod, 1, Vsns) of
	{value, {Mod, undefined, NewVsn}} ->
	    OldVsn = get_vsn(code:which(Mod)),
	    lists:keyreplace(Mod, 1, Vsns, {Mod, OldVsn, NewVsn});
	{value, {Mod, _OldVsn, _NewVsn}} ->
	    Vsns;
	false ->
	    OldVsn = get_vsn(code:which(Mod)),
	    [{Mod, OldVsn, undefined} | Vsns]
    end.

add_new_vsn(Mod, File, Vsns) ->
    NewVsn = get_vsn(File),
    case lists:keysearch(Mod, 1, Vsns) of
	{value, {Mod, OldVsn, undefined}} ->
	    lists:keyreplace(Mod, 1, Vsns, {Mod, OldVsn, NewVsn});
	false ->
	    [{Mod, undefined, NewVsn} | Vsns]
    end.



%%-----------------------------------------------------------------
%% Func: get_vsn/1
%% Args: File = string()
%% Purpose: Finds the version attribute of a module.
%% Returns: Vsn
%%          Vsn = term()
%%-----------------------------------------------------------------
get_vsn(File) ->
    {ok, {_Mod, Vsn}} = beam_lib:version(File),
    case misc_supp:is_string(Vsn) of
	true ->
	    Vsn;
	false ->
	    %% If -vsn(Vsn) defines a term which is not a
	    %% string, the value is returned here as [Vsn].
	    case Vsn of
		[VsnTerm] ->
		    VsnTerm;
		_ ->
		    Vsn
	    end
    end.