aboutsummaryrefslogblamecommitdiffstats
path: root/lib/mnesia/src/mnesia_locker.erl
blob: 9822dfd1161c28a11fad2182934eeed193377678 (plain) (tree)
1
2
3
4
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


                   
                                                        





































                                                                         

                          







                             

                                     





























































































































































































































































































































































































































































































































































































































                                                                                                             
                                            

























                                                                                  





















                                                         

























































































                                                                                


                                                  



                                             
                                                   











                                                           


                                                           


























































































































































































































































































































                                                                                           
                                                  



























































































                                                                                
%%
%% %CopyrightBegin%
%% 
%% Copyright Ericsson AB 1996-2011. 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(mnesia_locker).

-export([
	 get_held_locks/0,
	 get_lock_queue/0,
	 global_lock/5,
	 ixrlock/5,
	 init/1,
	 mnesia_down/2,
	 release_tid/1,
	 async_release_tid/2,
	 send_release_tid/2,
	 receive_release_tid_acc/2,
	 rlock/3,
	 rlock_table/3,
	 rwlock/3,
	 sticky_rwlock/3,
	 start/0,
	 sticky_wlock/3,
	 sticky_wlock_table/3,
	 wlock/3,
	 wlock_no_exist/4,
	 wlock_table/3,
	 load_lock_table/3
	]).

%% sys callback functions
-export([system_continue/3,
	 system_terminate/4,
	 system_code_change/4
	]).

-compile({no_auto_import,[error/2]}).

-include("mnesia.hrl").
-import(mnesia_lib, [dbg_out/2, error/2, verbose/2]).

-define(dbg(S,V), ok).
%-define(dbg(S,V), dbg_out("~p:~p: " ++ S, [?MODULE, ?LINE] ++ V)).

-define(ALL, '______WHOLETABLE_____').
-define(STICK, '______STICK_____').
-define(GLOBAL, '______GLOBAL_____').

-record(state, {supervisor}).

-record(queue, {oid, tid, op, pid, lucky}).

%% mnesia_held_locks: contain       {Oid, Op, Tid} entries  (bag)
-define(match_oid_held_locks(Oid),  {Oid, '_', '_'}).
%% mnesia_tid_locks: contain        {Tid, Oid, Op} entries  (bag) 
-define(match_oid_tid_locks(Tid),   {Tid, '_', '_'}).
%% mnesia_sticky_locks: contain     {Oid, Node} entries and {Tab, Node} entries (set)
-define(match_oid_sticky_locks(Oid),{Oid, '_'}).
%% mnesia_lock_queue: contain       {queue, Oid, Tid, Op, ReplyTo, WaitForTid} entries (bag)
-define(match_oid_lock_queue(Oid),  #queue{oid=Oid, tid='_', op = '_', pid = '_', lucky = '_'}). 
%% mnesia_lock_counter:             {{write, Tab}, Number} &&
%%                                  {{read, Tab}, Number} entries  (set)

start() ->
    mnesia_monitor:start_proc(?MODULE, ?MODULE, init, [self()]).

init(Parent) ->
    register(?MODULE, self()),
    process_flag(trap_exit, true),
    ?ets_new_table(mnesia_held_locks, [bag, private, named_table]), 
    ?ets_new_table(mnesia_tid_locks, [bag, private, named_table]),
    ?ets_new_table(mnesia_sticky_locks, [set, private, named_table]),
    ?ets_new_table(mnesia_lock_queue, [bag, private, named_table, {keypos, 2}]),
    
    proc_lib:init_ack(Parent, {ok, self()}),
    case ?catch_val(pid_sort_order) of
	r9b_plain -> put(pid_sort_order, r9b_plain);
	standard ->  put(pid_sort_order, standard);
	_ -> ignore
    end,
    loop(#state{supervisor = Parent}).

val(Var) ->
    case ?catch_val(Var) of
	{'EXIT', _ReASoN_} -> mnesia_lib:other_val(Var, _ReASoN_); 
	_VaLuE_ -> _VaLuE_ 
    end.

reply(From, R) ->
    From ! {?MODULE, node(), R}.

l_request(Node, X, Store) ->
    {?MODULE, Node} ! {self(), X},
    l_req_rec(Node, Store).

l_req_rec(Node, Store) ->
    ?ets_insert(Store, {nodes, Node}),
    receive 
	{?MODULE, Node, Reply} -> 
	    Reply;
	{mnesia_down, Node} -> 
	    {not_granted, {node_not_running, Node}}
    end.

release_tid(Tid) ->
    ?MODULE ! {release_tid, Tid}.

async_release_tid(Nodes, Tid) ->
    rpc:abcast(Nodes, ?MODULE, {release_tid, Tid}).

send_release_tid(Nodes, Tid) ->
    rpc:abcast(Nodes, ?MODULE, {self(), {sync_release_tid, Tid}}).

receive_release_tid_acc([Node | Nodes], Tid) ->
    receive 
	{?MODULE, Node, {tid_released, Tid}} -> 
	    receive_release_tid_acc(Nodes, Tid);
	{mnesia_down, Node} -> 
	    receive_release_tid_acc(Nodes, Tid)
    end;
receive_release_tid_acc([], _Tid) ->
    ok.

loop(State) ->
    receive
	{From, {write, Tid, Oid}} ->
	    try_sticky_lock(Tid, write, From, Oid),
	    loop(State);

	%% If Key == ?ALL it's a request to lock the entire table
	%%

	{From, {read, Tid, Oid}} ->
	    try_sticky_lock(Tid, read, From, Oid),
	    loop(State);

	%% Really do a  read, but get hold of a write lock
	%% used by mnesia:wread(Oid).
	
	{From, {read_write, Tid, Oid}} ->
	    try_sticky_lock(Tid, read_write, From, Oid),
	    loop(State);
	
	%% Tid has somehow terminated, clear up everything
	%% and pass locks on to queued processes.
	%% This is the purpose of the mnesia_tid_locks table
	
	{release_tid, Tid} ->
	    do_release_tid(Tid),
	    loop(State);
	
	%% stick lock, first tries this to the where_to_read Node
	{From, {test_set_sticky, Tid, {Tab, _} = Oid, Lock}} ->
	    case ?ets_lookup(mnesia_sticky_locks, Tab) of
		[] -> 
		    reply(From, not_stuck),
		    loop(State);
		[{_,Node}] when Node == node() ->
		    %% Lock is stuck here, see now if we can just set 
		    %% a regular write lock
		    try_lock(Tid, Lock, From, Oid),
		    loop(State);
		[{_,Node}] ->
		    reply(From, {stuck_elsewhere, Node}),
		    loop(State)
	    end;

	%% If test_set_sticky fails, we send this to all nodes
	%% after aquiring a real write lock on Oid

	{stick, {Tab, _}, N} ->
	    ?ets_insert(mnesia_sticky_locks, {Tab, N}),
	    loop(State);

	%% The caller which sends this message, must have first 
	%% aquired a write lock on the entire table
	{unstick, Tab} ->
	    ?ets_delete(mnesia_sticky_locks, Tab),
	    loop(State);

	{From, {ix_read, Tid, Tab, IxKey, Pos}} ->
	    case ?ets_lookup(mnesia_sticky_locks, Tab) of
		[] ->
		    set_read_lock_on_all_keys(Tid,From,Tab,IxKey,Pos),
		    loop(State);
		[{_,N}] when N == node() ->
		    set_read_lock_on_all_keys(Tid,From,Tab,IxKey,Pos),
		    loop(State);
		[{_,N}] ->
		    Req = {From, {ix_read, Tid, Tab, IxKey, Pos}},
		    From ! {?MODULE, node(), {switch, N, Req}},
		    loop(State)	   
	    end;

	{From, {sync_release_tid, Tid}} ->
	    do_release_tid(Tid),
	    reply(From, {tid_released, Tid}),
	    loop(State);
	
	{release_remote_non_pending, Node, Pending} ->
	    release_remote_non_pending(Node, Pending),
	    mnesia_monitor:mnesia_down(?MODULE, Node),
	    loop(State);

	{'EXIT', Pid, _} when Pid == State#state.supervisor ->
	    do_stop();

	{system, From, Msg} ->
	    verbose("~p got {system, ~p, ~p}~n", [?MODULE, From, Msg]),
	    Parent = State#state.supervisor,
	    sys:handle_system_msg(Msg, From, Parent, ?MODULE, [], State);

	{get_table, From, LockTable} ->
	    From ! {LockTable, ?ets_match_object(LockTable, '_')},
	    loop(State);
	
	Msg ->
	    error("~p got unexpected message: ~p~n", [?MODULE, Msg]),
	    loop(State)
    end.

set_lock(Tid, Oid, Op) ->
    ?dbg("Granted ~p ~p ~p~n", [Tid,Oid,Op]),
    ?ets_insert(mnesia_held_locks, {Oid, Op, Tid}),
    ?ets_insert(mnesia_tid_locks, {Tid, Oid, Op}).

%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Acquire locks

try_sticky_lock(Tid, Op, Pid, {Tab, _} = Oid) ->
    case ?ets_lookup(mnesia_sticky_locks, Tab) of
	[] ->
	    try_lock(Tid, Op, Pid, Oid);
	[{_,N}] when N == node() ->
	    try_lock(Tid, Op, Pid, Oid);
	[{_,N}] ->
	    Req = {Pid, {Op, Tid, Oid}},
	    Pid ! {?MODULE, node(), {switch, N, Req}}
    end.

try_lock(Tid, read_write, Pid, Oid) ->
    try_lock(Tid, read_write, read, write, Pid, Oid);
try_lock(Tid, Op, Pid, Oid) ->
    try_lock(Tid, Op, Op, Op, Pid, Oid).

try_lock(Tid, Op, SimpleOp, Lock, Pid, Oid) ->
    case can_lock(Tid, Lock, Oid, {no, bad_luck}) of
	yes ->
	    Reply = grant_lock(Tid, SimpleOp, Lock, Oid),
	    reply(Pid, Reply);
	{no, Lucky} ->
	    C = #cyclic{op = SimpleOp, lock = Lock, oid = Oid, lucky = Lucky},
	    ?dbg("Rejected ~p ~p ~p ~p ~n", [Tid, Oid, Lock, Lucky]),
	    reply(Pid, {not_granted, C});
	{queue, Lucky} ->
	    ?dbg("Queued ~p ~p ~p ~p ~n", [Tid, Oid, Lock, Lucky]),
	    %% Append to queue: Nice place for trace output
	    ?ets_insert(mnesia_lock_queue, 
			#queue{oid = Oid, tid = Tid, op = Op, 
			       pid = Pid, lucky = Lucky}),
	    ?ets_insert(mnesia_tid_locks, {Tid, Oid, {queued, Op}})
    end.

grant_lock(Tid, read, Lock, Oid = {Tab, Key})
  when Key /= ?ALL, Tab /= ?GLOBAL ->
    case node(Tid#tid.pid) == node() of
	true ->
	    set_lock(Tid, Oid, Lock),
	    {granted, lookup_in_client};
	false ->
	    try
		Val = mnesia_lib:db_get(Tab, Key), %% lookup as well
		set_lock(Tid, Oid, Lock),
		{granted, Val}
	    catch _:_Reason ->
		    %% Table has been deleted from this node,
		    %% restart the transaction.
		    C = #cyclic{op = read, lock = Lock, oid = Oid,
				lucky = nowhere},
		    {not_granted, C}
	    end
    end;
grant_lock(Tid, {ix_read,IxKey,Pos}, Lock, Oid = {Tab, _}) ->
    try
	Res = ix_read_res(Tab, IxKey,Pos),
	set_lock(Tid, Oid, Lock),
	{granted, Res, [?ALL]}
    catch _:_ ->
	    {not_granted, {no_exists, Tab, {index, [Pos]}}}
    end;
grant_lock(Tid, read, Lock, Oid) ->
    set_lock(Tid, Oid, Lock),
    {granted, ok};
grant_lock(Tid, write, Lock, Oid) ->
    set_lock(Tid, Oid, Lock),
    granted.

%% 1) Impose an ordering on all transactions favour old (low tid) transactions
%%    newer (higher tid) transactions may never wait on older ones,
%% 2) When releasing the tids from the queue always begin with youngest (high tid)
%%    because of 1) it will avoid the deadlocks.
%% 3) TabLocks is the problem :-) They should not starve and not deadlock 
%%    handle tablocks in queue as they had locks on unlocked records.

can_lock(Tid, read, {Tab, Key}, AlreadyQ) when Key /= ?ALL ->
    %% The key is bound, no need for the other BIF
    Oid = {Tab, Key}, 
    ObjLocks = ?ets_match_object(mnesia_held_locks, {Oid, write, '_'}),
    TabLocks = ?ets_match_object(mnesia_held_locks, {{Tab, ?ALL}, write, '_'}),
    check_lock(Tid, Oid, ObjLocks, TabLocks, yes, AlreadyQ, read);

can_lock(Tid, read, Oid, AlreadyQ) -> % Whole tab
    Tab = element(1, Oid),
    ObjLocks = ?ets_match_object(mnesia_held_locks, {{Tab, '_'}, write, '_'}),
    check_lock(Tid, Oid, ObjLocks, [], yes, AlreadyQ, read);

can_lock(Tid, write, {Tab, Key}, AlreadyQ) when Key /= ?ALL -> 
    Oid = {Tab, Key},
    ObjLocks = ?ets_lookup(mnesia_held_locks, Oid),
    TabLocks = ?ets_lookup(mnesia_held_locks, {Tab, ?ALL}),
    check_lock(Tid, Oid, ObjLocks, TabLocks, yes, AlreadyQ, write);

can_lock(Tid, write, Oid, AlreadyQ) -> % Whole tab
    Tab = element(1, Oid),
    ObjLocks = ?ets_match_object(mnesia_held_locks, ?match_oid_held_locks({Tab, '_'})),
    check_lock(Tid, Oid, ObjLocks, [], yes, AlreadyQ, write).

%% Check held locks for conflicting locks
check_lock(Tid, Oid, [Lock | Locks], TabLocks, X, AlreadyQ, Type) ->
    case element(3, Lock) of
	Tid ->
	    check_lock(Tid, Oid, Locks, TabLocks, X, AlreadyQ, Type);
	WaitForTid ->
	    Queue = allowed_to_be_queued(WaitForTid,Tid),
	    if Queue == true -> 
		    check_lock(Tid, Oid, Locks, TabLocks, {queue, WaitForTid}, AlreadyQ, Type);
	       Tid#tid.pid == WaitForTid#tid.pid ->
		    dbg_out("Spurious lock conflict ~w ~w: ~w -> ~w~n",
			    [Oid, Lock, Tid, WaitForTid]),  
		    %% Test..
		    {Tab, _Key} = Oid,
		    HaveQ = (ets:lookup(mnesia_lock_queue, Oid) /= []) 
			orelse (ets:lookup(mnesia_lock_queue,{Tab,?ALL}) /= []),
		    if 
			HaveQ -> 
			    {no, WaitForTid};
			true -> 
			    check_lock(Tid,Oid,Locks,TabLocks,{queue,WaitForTid},AlreadyQ,Type)
		    end;
		    %%{no, WaitForTid};  Safe solution 
	       true ->
		    {no, WaitForTid}
	    end
    end;

check_lock(_, _, [], [], X, {queue, bad_luck}, _) ->
    X;  %% The queue should be correct already no need to check it again

check_lock(_, _, [], [], X = {queue, _Tid}, _AlreadyQ, _) ->
    X;  

check_lock(Tid, Oid, [], [], X, AlreadyQ, Type) ->
    {Tab, Key} = Oid,
    if
	Type == write ->
	    check_queue(Tid, Tab, X, AlreadyQ);
	Key == ?ALL ->
	    %% hmm should be solvable by a clever select expr but not today...
	    check_queue(Tid, Tab, X, AlreadyQ);
	true ->
	    %% If there is a queue on that object, read_lock shouldn't be granted
	    ObjLocks = ets:lookup(mnesia_lock_queue, Oid),
	    case max(ObjLocks) of
		empty -> 
		    check_queue(Tid, Tab, X, AlreadyQ);
		ObjL ->
		    case allowed_to_be_queued(ObjL,Tid) of
			false ->
			    %% Starvation Preemption (write waits for read)
			    {no, ObjL};
			true ->
			    check_queue(Tid, Tab, {queue, ObjL}, AlreadyQ)
		    end
	    end
    end;

check_lock(Tid, Oid, [], TabLocks, X, AlreadyQ, Type) ->
    check_lock(Tid, Oid, TabLocks, [], X, AlreadyQ, Type).

%% True if  WaitForTid > Tid -> % Important order
allowed_to_be_queued(WaitForTid, Tid) ->
    case get(pid_sort_order) of
	undefined -> WaitForTid > Tid;
	r9b_plain -> 
	    cmp_tid(true, WaitForTid, Tid) =:= 1;
	standard  -> 
	    cmp_tid(false, WaitForTid, Tid) =:= 1
    end.	    
	    
%% Check queue for conflicting locks
%% Assume that all queued locks belongs to other tid's

check_queue(Tid, Tab, X, AlreadyQ) ->
    TabLocks = ets:lookup(mnesia_lock_queue, {Tab,?ALL}),
    Greatest = max(TabLocks),
    case Greatest of
	empty ->  X;
	Tid ->    X; 
	WaitForTid -> 
	    case allowed_to_be_queued(WaitForTid,Tid) of
		true ->
		    {queue, WaitForTid};
		false when AlreadyQ =:= {no, bad_luck} -> 
		    {no, WaitForTid}
	    end
    end.

sort_queue(QL) ->
    case get(pid_sort_order) of
	undefined -> 
	    lists:reverse(lists:keysort(#queue.tid, QL));
	r9b_plain -> 
	    lists:sort(fun(#queue{tid=X},#queue{tid=Y}) -> 
			       cmp_tid(true, X, Y) == 1
		       end, QL);
	standard  -> 
	    lists:sort(fun(#queue{tid=X},#queue{tid=Y}) ->
			       cmp_tid(false, X, Y) == 1
		       end, QL)
    end.

max([]) ->                 empty;
max([#queue{tid=Max}]) ->  Max;
max(L) ->
    [#queue{tid=Max}|_] = sort_queue(L),
    Max.

set_read_lock_on_all_keys(Tid, From, Tab, IxKey, Pos) ->
    Oid = {Tab,?ALL},
    Op = {ix_read,IxKey, Pos},
    Lock = read,
    case can_lock(Tid, Lock, Oid, {no, bad_luck}) of
	yes ->
	    Reply = grant_lock(Tid, Op, Lock, Oid),
	    reply(From, Reply);
	{no, Lucky} ->
	    C = #cyclic{op = Op, lock = Lock, oid = Oid, lucky = Lucky},
	    ?dbg("Rejected ~p ~p ~p ~p ~n", [Tid, Oid, Lock, Lucky]),
	    reply(From, {not_granted, C});
    	{queue, Lucky} ->
	    ?dbg("Queued ~p ~p ~p ~p ~n", [Tid, Oid, Lock, Lucky]),
	    %% Append to queue: Nice place for trace output
	    ?ets_insert(mnesia_lock_queue, 
			#queue{oid = Oid, tid = Tid, op = Op, 
			       pid = From, lucky = Lucky}),
	    ?ets_insert(mnesia_tid_locks, {Tid, Oid, {queued, Op}})
    end.
       
%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% Release of locks

%% Release remote non-pending nodes
release_remote_non_pending(Node, Pending) ->
    %% Clear the mnesia_sticky_locks table first, to avoid
    %% unnecessary requests to the failing node
    ?ets_match_delete(mnesia_sticky_locks, {'_' , Node}),

    %% Then we have to release all locks held by processes
    %% running at the failed node and also simply remove all
    %% queue'd requests back to the failed node

    AllTids = ?ets_match(mnesia_tid_locks, {'$1', '_', '_'}),
    Tids = [T || [T] <- AllTids, Node == node(T#tid.pid), not lists:member(T, Pending)],
    do_release_tids(Tids).

do_release_tids([Tid | Tids]) ->
    do_release_tid(Tid),
    do_release_tids(Tids);
do_release_tids([]) ->
    ok.

do_release_tid(Tid) ->
    Locks = ?ets_lookup(mnesia_tid_locks, Tid),
    ?dbg("Release ~p ~p ~n", [Tid, Locks]),
    ?ets_delete(mnesia_tid_locks, Tid),
    release_locks(Locks),
    %% Removed queued locks which has had locks
    UniqueLocks = keyunique(lists:sort(Locks),[]),
    rearrange_queue(UniqueLocks).

keyunique([{_Tid, Oid, _Op}|R], Acc = [{_, Oid, _}|_]) ->
    keyunique(R, Acc);
keyunique([H|R], Acc) ->
    keyunique(R, [H|Acc]);
keyunique([], Acc) ->
    Acc.

release_locks([Lock | Locks]) ->
    release_lock(Lock),
    release_locks(Locks);
release_locks([]) ->
    ok.

release_lock({Tid, Oid, {queued, _}}) ->
    ?ets_match_delete(mnesia_lock_queue, #queue{oid=Oid, tid = Tid, op = '_',
						pid = '_', lucky = '_'});
release_lock({Tid, Oid, Op}) ->
    if
	Op == write ->
	    ?ets_delete(mnesia_held_locks, Oid);
	Op == read ->
	    ets:delete_object(mnesia_held_locks, {Oid, Op, Tid})
    end.

rearrange_queue([{_Tid, {Tab, Key}, _} | Locks]) ->
    if
	Key /= ?ALL->	    
	    Queue =  
		ets:lookup(mnesia_lock_queue, {Tab, ?ALL}) ++ 
		ets:lookup(mnesia_lock_queue, {Tab, Key}),
	    case Queue of 
		[] -> 
		    ok;
		_ ->
		    Sorted = sort_queue(Queue),
		    try_waiters_obj(Sorted)
	    end;	
	true -> 
	    Pat = ?match_oid_lock_queue({Tab, '_'}),
	    Queue = ?ets_match_object(mnesia_lock_queue, Pat),	    
	    Sorted = sort_queue(Queue),
	    try_waiters_tab(Sorted)
    end,
    ?dbg("RearrQ ~p~n", [Queue]),
    rearrange_queue(Locks);
rearrange_queue([]) ->
    ok.

try_waiters_obj([W | Waiters]) ->
    case try_waiter(W) of
	queued ->
	    no;
	_ -> 	    
	    try_waiters_obj(Waiters)
    end;
try_waiters_obj([]) ->
    ok.

try_waiters_tab([W | Waiters]) ->
    case W#queue.oid of
	{_Tab, ?ALL} ->
	    case try_waiter(W) of
		queued ->
		    no;
		_ ->
		    try_waiters_tab(Waiters)
	    end;
	Oid ->
	    case try_waiter(W) of
		queued -> 	    
		    Rest = key_delete_all(Oid, #queue.oid, Waiters),
		    try_waiters_tab(Rest);
		_ ->		    
		    try_waiters_tab(Waiters)
	    end
    end;
try_waiters_tab([]) ->
    ok.

try_waiter({queue, Oid, Tid, read_write, ReplyTo, _}) ->
    try_waiter(Oid, read_write, read, write, ReplyTo, Tid);
try_waiter({queue, Oid, Tid, IXR = {ix_read,_,_}, ReplyTo, _}) ->
    try_waiter(Oid, IXR, IXR, read, ReplyTo, Tid);
try_waiter({queue, Oid, Tid, Op, ReplyTo, _}) ->
    try_waiter(Oid, Op, Op, Op, ReplyTo, Tid).

try_waiter(Oid, Op, SimpleOp, Lock, ReplyTo, Tid) ->
    case can_lock(Tid, Lock, Oid, {queue, bad_luck}) of
	yes ->
	    %% Delete from queue: Nice place for trace output
	    ?ets_match_delete(mnesia_lock_queue, 
			      #queue{oid=Oid, tid = Tid, op = Op,
				     pid = ReplyTo, lucky = '_'}),
	    Reply = grant_lock(Tid, SimpleOp, Lock, Oid),	    
	    reply(ReplyTo,Reply),
	    locked;
	{queue, _Why} ->
	    ?dbg("Keep ~p ~p ~p ~p~n", [Tid, Oid, Lock, _Why]),
	    queued; % Keep waiter in queue	
	{no, Lucky} ->
	    C = #cyclic{op = SimpleOp, lock = Lock, oid = Oid, lucky = Lucky},
	    verbose("** WARNING ** Restarted transaction, possible deadlock in lock queue ~w: cyclic = ~w~n",
		    [Tid, C]),
	    ?ets_match_delete(mnesia_lock_queue, 
			      #queue{oid=Oid, tid = Tid, op = Op,
				     pid = ReplyTo, lucky = '_'}),
	    Reply = {not_granted, C},
	    reply(ReplyTo,Reply),
	    removed
    end.

key_delete_all(Key, Pos, TupleList) ->
    key_delete_all(Key, Pos, TupleList, []).
key_delete_all(Key, Pos, [H|T], Ack) when element(Pos, H) == Key ->
    key_delete_all(Key, Pos, T, Ack);
key_delete_all(Key, Pos, [H|T], Ack) ->
    key_delete_all(Key, Pos, T, [H|Ack]);
key_delete_all(_, _, [], Ack) ->
    lists:reverse(Ack).

ix_read_res(Tab,IxKey,Pos) ->
    Index = mnesia_index:get_index_table(Tab, Pos),
    Rks = mnesia_lib:elems(2,mnesia_index:db_get(Index, IxKey)),
    lists:append(lists:map(fun(Real) -> mnesia_lib:db_get(Tab, Real) end, Rks)).

%% ********************* end server code ********************
%% The following code executes at the client side of a transactions

mnesia_down(N, Pending) ->
    case whereis(?MODULE) of
	undefined ->
	    %% Takes care of mnesia_down's in early startup
	    mnesia_monitor:mnesia_down(?MODULE, N);
	Pid ->
	    %% Syncronously call needed in order to avoid
	    %% race with mnesia_tm's coordinator processes
	    %% that may restart and acquire new locks.
	    %% mnesia_monitor ensures the sync.
	    Pid ! {release_remote_non_pending, N, Pending}
    end.

%% Aquire a write lock, but do a read, used by 
%% mnesia:wread/1

rwlock(Tid, Store, Oid) ->
    {Tab, Key} = Oid,
    case val({Tab, where_to_read}) of
	nowhere ->
	    mnesia:abort({no_exists, Tab});
	Node ->
	    Lock = write,
	    case need_lock(Store, Tab, Key, Lock)  of
		yes ->
		    Ns = w_nodes(Tab),
		    check_majority(Tab, Ns),
		    Res = get_rwlocks_on_nodes(Ns, rwlock, Node, Store, Tid, Oid),
		    ?ets_insert(Store, {{locks, Tab, Key}, Lock}),
		    Res;
		no ->
		    if
			Key == ?ALL ->
			    w_nodes(Tab);
			Tab == ?GLOBAL ->
			    w_nodes(Tab);
			true ->
			    dirty_rpc(Node, Tab, Key, Lock)
		    end
	    end
    end.

%% Return a list of nodes or abort transaction
%% WE also insert any additional where_to_write nodes
%% in the local store under the key == nodes

w_nodes(Tab) ->
    Nodes = ?catch_val({Tab, where_to_write}),
    case Nodes of
	[_ | _] -> Nodes;
	_ ->  mnesia:abort({no_exists, Tab})
    end.

%% If the table has the 'majority' flag set, we can
%% only take a write lock if we see a majority of the
%% nodes.

check_majority(true, Tab, HaveNs) ->
    check_majority(Tab, HaveNs);
check_majority(false, _, _) ->
    ok.

check_majority(Tab, HaveNs) ->
    case ?catch_val({Tab, majority}) of
	true ->
	    case mnesia_lib:have_majority(Tab, HaveNs) of
		true ->
		    ok;
		false ->
		    mnesia:abort({no_majority, Tab})
	    end;
	_ ->
	    ok
    end.

%% aquire a sticky wlock, a sticky lock is a lock
%% which remains at this node after the termination of the
%% transaction.

sticky_wlock(Tid, Store, Oid) ->
    sticky_lock(Tid, Store, Oid, write).

sticky_rwlock(Tid, Store, Oid) ->
    sticky_lock(Tid, Store, Oid, read_write).

sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
    N = val({Tab, where_to_read}), 
    if
	node() == N ->
	    case need_lock(Store, Tab, Key, write) of
	    	yes ->
		    do_sticky_lock(Tid, Store, Oid, Lock);
		no ->
		    dirty_sticky_lock(Tab, Key, [N], Lock)
	    end;
	true ->
	    mnesia:abort({not_local, Tab})
    end.

do_sticky_lock(Tid, Store, {Tab, Key} = Oid, Lock) ->
    ?MODULE ! {self(), {test_set_sticky, Tid, Oid, Lock}},
    N = node(),
    receive
	{?MODULE, N, granted} ->
	    ?ets_insert(Store, {{locks, Tab, Key}, write}),
	    [?ets_insert(Store, {nodes, Node}) || Node <- w_nodes(Tab)],
	    granted;
	{?MODULE, N, {granted, Val}} -> %% for rwlocks
	    case opt_lookup_in_client(Val, Oid, write) of
		C = #cyclic{} ->
		    exit({aborted, C});
		Val2 ->
		    ?ets_insert(Store, {{locks, Tab, Key}, write}),
		    [?ets_insert(Store, {nodes, Node}) || Node <- w_nodes(Tab)],
		    Val2
	    end;
	{?MODULE, N, {not_granted, Reason}} ->
	    exit({aborted, Reason});
	{?MODULE, N, not_stuck} ->
	    not_stuck(Tid, Store, Tab, Key, Oid, Lock, N),
	    dirty_sticky_lock(Tab, Key, [N], Lock);
	{mnesia_down, Node} ->
	    EMsg = {aborted, {node_not_running, Node}},
	    flush_remaining([N], Node, EMsg);
	{?MODULE, N, {stuck_elsewhere, _N2}} ->
	    stuck_elsewhere(Tid, Store, Tab, Key, Oid, Lock),
	    dirty_sticky_lock(Tab, Key, [N], Lock)
    end.

not_stuck(Tid, Store, Tab, _Key, Oid, _Lock, N) ->
    rlock(Tid, Store, {Tab, ?ALL}),   %% needed?
    wlock(Tid, Store, Oid),           %% perfect sync
    wlock(Tid, Store, {Tab, ?STICK}), %% max one sticker/table
    Ns = val({Tab, where_to_write}),
    rpc:abcast(Ns, ?MODULE, {stick, Oid, N}).

stuck_elsewhere(Tid, Store, Tab, _Key, Oid, _Lock) ->
    rlock(Tid, Store, {Tab, ?ALL}),   %% needed?
    wlock(Tid, Store, Oid),           %% perfect sync
    wlock(Tid, Store, {Tab, ?STICK}), %% max one sticker/table
    Ns = val({Tab, where_to_write}),
    rpc:abcast(Ns, ?MODULE, {unstick, Tab}).

dirty_sticky_lock(Tab, Key, Nodes, Lock) ->
    if
	Lock == read_write ->
	    mnesia_lib:db_get(Tab, Key);
	Key == ?ALL ->
	    Nodes;
	Tab == ?GLOBAL ->
	    Nodes;
	true ->
	    ok
    end.

sticky_wlock_table(Tid, Store, Tab) ->
    sticky_lock(Tid, Store, {Tab, ?ALL}, write).

%% aquire a wlock on Oid
%% We store a {Tabname, write, Tid} in all locktables
%% on all nodes containing a copy of Tabname
%% We also store an item {{locks, Tab, Key}, write} in the 
%% local store when we have aquired the lock.
%% 
wlock(Tid, Store, Oid) ->
    wlock(Tid, Store, Oid, _CheckMajority = true).

wlock(Tid, Store, Oid, CheckMajority) ->
    {Tab, Key} = Oid,
    case need_lock(Store, Tab, Key, write) of
	yes ->
	    Ns = w_nodes(Tab),
	    check_majority(CheckMajority, Tab, Ns),
	    Op = {self(), {write, Tid, Oid}},
	    ?ets_insert(Store, {{locks, Tab, Key}, write}),
	    get_wlocks_on_nodes(Ns, Ns, Store, Op, Oid);
	no when Key /= ?ALL, Tab /= ?GLOBAL ->
	    [];
	no ->
	    w_nodes(Tab)
    end.

wlock_table(Tid, Store, Tab) ->
    wlock(Tid, Store, {Tab, ?ALL}).

load_lock_table(Tid, Store, Tab) ->
    wlock(Tid, Store, {Tab, ?ALL}, _CheckMajority = false).

%% Write lock even if the table does not exist

wlock_no_exist(Tid, Store, Tab, Ns) ->
    Oid = {Tab, ?ALL},
    Op = {self(), {write, Tid, Oid}},
    get_wlocks_on_nodes(Ns, Ns, Store, Op, Oid).

need_lock(Store, Tab, Key, LockPattern) ->
    TabL = ?ets_match_object(Store, {{locks, Tab, ?ALL}, LockPattern}),
    if 
	TabL == [] ->
	    KeyL = ?ets_match_object(Store, {{locks, Tab, Key}, LockPattern}),
	    if 
		KeyL == [] ->
		    yes;
		true  ->
		    no
	    end;
	true ->
	    no
    end.

add_debug(Nodes) ->  % Use process dictionary for debug info
    put(mnesia_wlock_nodes, Nodes).

del_debug() ->
    erase(mnesia_wlock_nodes).

%% We first send lock request to the local node if it is part of the lockers
%% then the first sorted node then to the rest of the lockmanagers on all 
%% nodes holding a copy of the table

get_wlocks_on_nodes([Node | Tail], Orig, Store, Request, Oid) ->
    {?MODULE, Node} ! Request,
    ?ets_insert(Store, {nodes, Node}),
    receive_wlocks([Node], undefined, Store, Oid),
    case node() of
	Node -> %% Local done try one more
	    get_wlocks_on_nodes(Tail, Orig, Store, Request, Oid);
	_ ->    %% The first succeded cont with the rest  
	    get_wlocks_on_nodes(Tail, Store, Request),
	    receive_wlocks(Tail, Orig, Store, Oid)
    end;
get_wlocks_on_nodes([], Orig, _Store, _Request, _Oid) -> 
    Orig.

get_wlocks_on_nodes([Node | Tail], Store, Request) ->
    {?MODULE, Node} ! Request,
    ?ets_insert(Store,{nodes, Node}),
    get_wlocks_on_nodes(Tail, Store, Request);
get_wlocks_on_nodes([], _, _) -> 
    ok.

get_rwlocks_on_nodes([ReadNode|Tail], _Res, ReadNode, Store, Tid, Oid) ->
    Op = {self(), {read_write, Tid, Oid}},
    {?MODULE, ReadNode} ! Op,
    ?ets_insert(Store, {nodes, ReadNode}),
    Res = receive_wlocks([ReadNode], undefined, Store, Oid),
    case node() of
	ReadNode -> 
	    get_rwlocks_on_nodes(Tail, Res, ReadNode, Store, Tid, Oid);
	_ ->
	    get_wlocks_on_nodes(Tail, Store, {self(), {write, Tid, Oid}}),
	    receive_wlocks(Tail, Res, Store, Oid)
    end;
get_rwlocks_on_nodes([Node | Tail], Res, ReadNode, Store, Tid, Oid) ->
    Op = {self(), {write, Tid, Oid}},
    {?MODULE, Node} ! Op,
    ?ets_insert(Store, {nodes, Node}),
    receive_wlocks([Node], undefined, Store, Oid),
    if node() == Node ->
	    get_rwlocks_on_nodes(Tail, Res, ReadNode, Store, Tid, Oid);
       Res == rwlock -> %% Hmm	    
	    Rest = lists:delete(ReadNode, Tail),
	    Op2 = {self(), {read_write, Tid, Oid}},
	    {?MODULE, ReadNode} ! Op2,
	    ?ets_insert(Store, {nodes, ReadNode}),
	    get_wlocks_on_nodes(Rest, Store, {self(), {write, Tid, Oid}}),
	    receive_wlocks([ReadNode|Rest], undefined, Store, Oid);
       true ->
	    get_wlocks_on_nodes(Tail, Store, {self(), {write, Tid, Oid}}),
	    receive_wlocks(Tail, Res, Store, Oid)
    end;
get_rwlocks_on_nodes([],Res,_,_,_,_) ->
    Res.

receive_wlocks([], Res, _Store, _Oid) ->
    del_debug(),
    Res;
receive_wlocks(Nodes = [This|Ns], Res, Store, Oid) ->
    add_debug(Nodes),
    receive
	{?MODULE, Node, granted} ->
	    receive_wlocks(lists:delete(Node,Nodes), Res, Store, Oid);
	{?MODULE, Node, {granted, Val}} -> %% for rwlocks
	    case opt_lookup_in_client(Val, Oid, write) of
		C = #cyclic{} ->
		    flush_remaining(Nodes, Node, {aborted, C});
		Val2 ->
		    receive_wlocks(lists:delete(Node,Nodes), Val2, Store, Oid)
	    end;
	{?MODULE, Node, {not_granted, Reason}} ->
	    Reason1 = {aborted, Reason},
	    flush_remaining(Nodes,Node,Reason1);
	{?MODULE, Node, {switch, Sticky, _Req}} -> %% for rwlocks
	    Tail = lists:delete(Node,Nodes),
	    Nonstuck = lists:delete(Sticky,Tail),
	    [?ets_insert(Store, {nodes, NSNode}) || NSNode <- Nonstuck],
	    case lists:member(Sticky,Tail) of		
		true -> 		    
		    sticky_flush(Nonstuck,Store),
		    receive_wlocks([Sticky], Res, Store, Oid);
		false ->
		    sticky_flush(Nonstuck,Store),
		    Res
	    end;
	{mnesia_down, This} ->  % Only look for down from Nodes in list
	    Reason1 = {aborted, {node_not_running, This}},
	    flush_remaining(Ns, This, Reason1)
    end.

sticky_flush([], _) -> 
    del_debug(),
    ok;
sticky_flush(Ns=[Node | Tail], Store) ->
    add_debug(Ns),
    receive
	{?MODULE, Node, _} ->
	    sticky_flush(Tail, Store);
	{mnesia_down, Node} ->
	    Reason1 = {aborted, {node_not_running, Node}},
	    flush_remaining(Tail, Node, Reason1)
    end.

flush_remaining([], _SkipNode, Res) ->
    del_debug(),
    exit(Res);
flush_remaining([SkipNode | Tail ], SkipNode, Res) ->
    flush_remaining(Tail, SkipNode, Res);
flush_remaining(Ns=[Node | Tail], SkipNode, Res) ->
    add_debug(Ns),
    receive
	{?MODULE, Node, _} ->
	    flush_remaining(Tail, SkipNode, Res);
	{mnesia_down, Node} ->
	    flush_remaining(Tail, SkipNode, {aborted, {node_not_running, Node}})
    end.

opt_lookup_in_client(lookup_in_client, Oid, Lock) ->
    {Tab, Key} = Oid,
    case catch mnesia_lib:db_get(Tab, Key) of
	{'EXIT', _} ->
	    %% Table has been deleted from this node,
	    %% restart the transaction.
	    #cyclic{op = read, lock = Lock, oid = Oid, lucky = nowhere};
	Val -> 
	    Val
    end;
opt_lookup_in_client(Val, _Oid, _Lock) ->
    Val.

return_granted_or_nodes({_, ?ALL}   , Nodes) -> Nodes;
return_granted_or_nodes({?GLOBAL, _}, Nodes) -> Nodes;
return_granted_or_nodes(_           , _Nodes) -> granted.
    
%% We store a {Tab, read, From} item in the 
%% locks table on the node where we actually do pick up the object
%% and we also store an item {lock, Oid, read} in our local store
%% so that we can release any locks we hold when we commit.
%% This function not only aquires a read lock, but also reads the object

%% Oid's are always {Tab, Key} tuples
rlock(Tid, Store, Oid) ->
    {Tab, Key} = Oid,
    case val({Tab, where_to_read}) of
	nowhere ->
	    mnesia:abort({no_exists, Tab});
	Node ->
	    case need_lock(Store, Tab, Key, '_') of
		yes ->
		    R = l_request(Node, {read, Tid, Oid}, Store),
		    rlock_get_reply(Node, Store, Oid, R);
		no ->
		    if
			Key == ?ALL ->
			    [Node];
			Tab == ?GLOBAL ->
			    [Node];
			true ->
			    dirty_rpc(Node, Tab, Key, read)
		    end
	    end
    end.

dirty_rpc(nowhere, Tab, Key, _Lock) ->
    mnesia:abort({no_exists, {Tab, Key}});
dirty_rpc(Node, _Tab, ?ALL, _Lock) ->
    [Node];
dirty_rpc(Node, ?GLOBAL, _Key, _Lock) ->
    [Node];
dirty_rpc(Node, Tab, Key, Lock) ->
    Args = [Tab, Key],
    case rpc:call(Node, mnesia_lib, db_get, Args) of
	{badrpc, Reason} ->
	    case val({Tab, where_to_read}) of
		Node ->
		    ErrorTag = mnesia_lib:dirty_rpc_error_tag(Reason),
		    mnesia:abort({ErrorTag, Args});
		_NewNode ->
		    %% Table has been deleted from the node,
		    %% restart the transaction.
		    C = #cyclic{op = read, lock = Lock, oid = {Tab, Key}, lucky = nowhere},
		    exit({aborted, C})
	    end;
	Other ->
	    Other
    end.

rlock_get_reply(Node, Store, Oid, {granted, V}) ->
    {Tab, Key} = Oid,
    ?ets_insert(Store, {{locks, Tab, Key}, read}),
    ?ets_insert(Store, {nodes, Node}),
    case opt_lookup_in_client(V, Oid, read) of
	C = #cyclic{} -> 
	    mnesia:abort(C);
	Val -> 
	    Val
    end;
rlock_get_reply(Node, Store, Oid, granted) ->
    {Tab, Key} = Oid,
    ?ets_insert(Store, {{locks, Tab, Key}, read}),
    ?ets_insert(Store, {nodes, Node}),
    return_granted_or_nodes(Oid, [Node]);
rlock_get_reply(Node, Store, Tab, {granted, V, RealKeys}) ->
    %% Kept for backwards compatibility, keep until no old nodes
    %% are available
    L = fun(K) -> ?ets_insert(Store, {{locks, Tab, K}, read}) end,
    lists:foreach(L, RealKeys),
    ?ets_insert(Store, {nodes, Node}),
    V;
rlock_get_reply(_Node, _Store, _Oid, {not_granted, Reason}) ->
    exit({aborted, Reason});

rlock_get_reply(_Node, Store, Oid, {switch, N2, Req}) ->    
    ?ets_insert(Store, {nodes, N2}),
    {?MODULE, N2} ! Req,
    rlock_get_reply(N2, Store, Oid, l_req_rec(N2, Store)).

rlock_table(Tid, Store, Tab) ->
    rlock(Tid, Store, {Tab, ?ALL}).

ixrlock(Tid, Store, Tab, IxKey, Pos) ->
    case val({Tab, where_to_read}) of
	nowhere ->
	    mnesia:abort({no_exists, Tab});
	Node ->
	    %%% Old code
	    %% R = l_request(Node, {ix_read, Tid, Tab, IxKey, Pos}, Store),
	    %% rlock_get_reply(Node, Store, Tab, R)
	    
	    case need_lock(Store, Tab, ?ALL, read) of
		no when Node =:= node() ->
		    ix_read_res(Tab,IxKey,Pos);
		_ -> %% yes or need to get the result from other node
		    R = l_request(Node, {ix_read, Tid, Tab, IxKey, Pos}, Store),
		    rlock_get_reply(Node, Store, Tab, R)
	    end
    end.

%% Grabs the locks or exits
global_lock(Tid, Store, Item, write, Ns) ->
    Oid = {?GLOBAL, Item},
    Op = {self(), {write, Tid, Oid}},
    get_wlocks_on_nodes(Ns, Ns, Store, Op, Oid);
global_lock(Tid, Store, Item, read, Ns) ->
    Oid = {?GLOBAL, Item},
    send_requests(Ns, {read, Tid, Oid}),
    rec_requests(Ns, Oid, Store),
    Ns.

send_requests([Node | Nodes], X) ->
    {?MODULE, Node} ! {self(), X},
    send_requests(Nodes, X);
send_requests([], _X) ->
    ok.

rec_requests([Node | Nodes], Oid, Store) ->
    Res = l_req_rec(Node, Store),
    case catch rlock_get_reply(Node, Store, Oid, Res) of
	{'EXIT', Reason} ->
	    flush_remaining(Nodes, Node, Reason);
	_ ->
	    rec_requests(Nodes, Oid, Store)
    end;
rec_requests([], _Oid, _Store) ->
    ok.

get_held_locks() ->
    ?MODULE ! {get_table, self(), mnesia_held_locks},
    receive {mnesia_held_locks, Locks} -> Locks  end.

get_lock_queue() ->
    ?MODULE ! {get_table, self(), mnesia_lock_queue},
    Q = receive {mnesia_lock_queue, Locks} -> Locks  end,
    [{Oid, Op, Pid, Tid, WFT} || {queue, Oid, Tid, Op, Pid, WFT} <- Q].

do_stop() ->
    exit(shutdown).

%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% System upgrade

system_continue(_Parent, _Debug, State) ->
    loop(State).

-spec system_terminate(_, _, _, _) -> no_return().
system_terminate(_Reason, _Parent, _Debug, _State) ->
    do_stop().

system_code_change(State, _Module, _OldVsn, _Extra) ->
    {ok, State}.


%%%%%%%%%%%%%%%%%%%%%%%%%%%
%% AXD301 patch sort pids according to R9B sort order
%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% Om R9B == true, g�rs j�mf�relsen som i R9B plain.
%% Om R9B == false, g�rs j�mf�relsen som i alla andra releaser.
%% cmp_tid(T1, T2) returnerar -1 om T1 < T2, 0 om T1 = T2 och 1 om T1 > T2.

-define(VERSION_MAGIC,       131).
-define(ATOM_EXT,            100).
-define(PID_EXT,             103).

-record(pid_info, {serial, number, nodename, creation}).

cmp_tid(R9B,
	#tid{} = T,
	#tid{} = T) when R9B == true; R9B == false ->
    0;
cmp_tid(R9B,
	#tid{counter = C, pid = Pid1},
	#tid{counter = C, pid = Pid2}) when R9B == true; R9B == false ->
    cmp_pid_info(R9B, pid_to_pid_info(Pid1), pid_to_pid_info(Pid2));
cmp_tid(R9B,
	#tid{counter = C1},
	#tid{counter = C2}) when R9B == true; R9B == false ->
    cmp(C1, C2).

cmp_pid_info(_, #pid_info{} = PI, #pid_info{} = PI) ->
    0;
cmp_pid_info(false,
	     #pid_info{serial = S, number = N, nodename = NN, creation = C1},
	     #pid_info{serial = S, number = N, nodename = NN, creation = C2}) ->
    cmp(C1, C2);
cmp_pid_info(false,
	     #pid_info{serial = S, number = N, nodename = NN1},
	     #pid_info{serial = S, number = N, nodename = NN2}) ->
    cmp(NN1, NN2);
cmp_pid_info(false,
	     #pid_info{serial = S, number = N1},
	     #pid_info{serial = S, number = N2}) ->
    cmp(N1, N2);
cmp_pid_info(false, #pid_info{serial = S1}, #pid_info{serial = S2}) ->
    cmp(S1, S2);
cmp_pid_info(true,
	     #pid_info{nodename = NN, creation = C, serial = S, number = N1},
	     #pid_info{nodename = NN, creation = C, serial = S, number = N2}) ->
    cmp(N1, N2);
cmp_pid_info(true,
	     #pid_info{nodename = NN, creation = C, serial = S1},
	     #pid_info{nodename = NN, creation = C, serial = S2}) ->
    cmp(S1, S2);
cmp_pid_info(true,
	     #pid_info{nodename = NN, creation = C1},
	     #pid_info{nodename = NN, creation = C2}) ->
    cmp(C1, C2);
cmp_pid_info(true, #pid_info{nodename = NN1}, #pid_info{nodename = NN2}) ->
    cmp(NN1, NN2).

cmp(X, X) -> 0;
cmp(X1, X2) when X1 < X2 -> -1;
cmp(_X1, _X2) -> 1.

pid_to_pid_info(Pid) when is_pid(Pid) ->
    [?VERSION_MAGIC, ?PID_EXT, ?ATOM_EXT, NNL1, NNL0 | Rest]
	= binary_to_list(term_to_binary(Pid)),
    [N3, N2, N1, N0, S3, S2, S1, S0, Creation] = drop(bytes2int(NNL1, NNL0),
						      Rest),
    #pid_info{serial = bytes2int(S3, S2, S1, S0),
	      number = bytes2int(N3, N2, N1, N0),
	      nodename = node(Pid),
	      creation = Creation}.

drop(0, L) -> L;
drop(N, [_|L]) when is_integer(N), N > 0 -> drop(N-1, L);
drop(N, []) when is_integer(N), N > 0 -> [].

bytes2int(N1, N0) when 0 =< N1, N1 =< 255,
		       0 =< N0, N0 =< 255 ->
    (N1 bsl 8) bor N0.
bytes2int(N3, N2, N1, N0) when 0 =< N3, N3 =< 255,
			       0 =< N2, N2 =< 255,
			       0 =< N1, N1 =< 255,
			       0 =< N0, N0 =< 255 ->
    (N3 bsl 24) bor (N2 bsl 16) bor (N1 bsl 8) bor N0.