File: gthread.c

package info (click to toggle)
glib2.0 2.58.3-2+deb10u2
  • links: PTS, VCS
  • area: main
  • in suites: bullseye, buster, buster-backports, sid
  • size: 48,956 kB
  • sloc: ansic: 452,656; xml: 16,781; python: 6,149; makefile: 3,776; sh: 1,499; perl: 1,140; cpp: 9
file content (1066 lines) | stat: -rw-r--r-- 32,884 bytes parent folder | download
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
/* GLIB - Library of useful routines for C programming
 * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
 *
 * gthread.c: MT safety related functions
 * Copyright 1998 Sebastian Wilhelmi; University of Karlsruhe
 *                Owen Taylor
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

/* Prelude {{{1 ----------------------------------------------------------- */

/*
 * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
 * file for a list of people on the GLib Team.  See the ChangeLog
 * files for a list of changes.  These files are distributed with
 * GLib at ftp://ftp.gtk.org/pub/gtk/.
 */

/*
 * MT safe
 */

/* implement gthread.h's inline functions */
#define G_IMPLEMENT_INLINES 1
#define __G_THREAD_C__

#include "config.h"

#include "gthread.h"
#include "gthreadprivate.h"

#include <string.h>

#ifdef G_OS_UNIX
#include <unistd.h>
#endif

#ifndef G_OS_WIN32
#include <sys/time.h>
#include <time.h>
#else
#include <windows.h>
#endif /* G_OS_WIN32 */

#include "gslice.h"
#include "gstrfuncs.h"
#include "gtestutils.h"
#include "glib_trace.h"

/**
 * SECTION:threads
 * @title: Threads
 * @short_description: portable support for threads, mutexes, locks,
 *     conditions and thread private data
 * @see_also: #GThreadPool, #GAsyncQueue
 *
 * Threads act almost like processes, but unlike processes all threads
 * of one process share the same memory. This is good, as it provides
 * easy communication between the involved threads via this shared
 * memory, and it is bad, because strange things (so called
 * "Heisenbugs") might happen if the program is not carefully designed.
 * In particular, due to the concurrent nature of threads, no
 * assumptions on the order of execution of code running in different
 * threads can be made, unless order is explicitly forced by the
 * programmer through synchronization primitives.
 *
 * The aim of the thread-related functions in GLib is to provide a
 * portable means for writing multi-threaded software. There are
 * primitives for mutexes to protect the access to portions of memory
 * (#GMutex, #GRecMutex and #GRWLock). There is a facility to use
 * individual bits for locks (g_bit_lock()). There are primitives
 * for condition variables to allow synchronization of threads (#GCond).
 * There are primitives for thread-private data - data that every
 * thread has a private instance of (#GPrivate). There are facilities
 * for one-time initialization (#GOnce, g_once_init_enter()). Finally,
 * there are primitives to create and manage threads (#GThread).
 *
 * The GLib threading system used to be initialized with g_thread_init().
 * This is no longer necessary. Since version 2.32, the GLib threading
 * system is automatically initialized at the start of your program,
 * and all thread-creation functions and synchronization primitives
 * are available right away.
 *
 * Note that it is not safe to assume that your program has no threads
 * even if you don't call g_thread_new() yourself. GLib and GIO can
 * and will create threads for their own purposes in some cases, such
 * as when using g_unix_signal_source_new() or when using GDBus.
 *
 * Originally, UNIX did not have threads, and therefore some traditional
 * UNIX APIs are problematic in threaded programs. Some notable examples
 * are
 * 
 * - C library functions that return data in statically allocated
 *   buffers, such as strtok() or strerror(). For many of these,
 *   there are thread-safe variants with a _r suffix, or you can
 *   look at corresponding GLib APIs (like g_strsplit() or g_strerror()).
 *
 * - The functions setenv() and unsetenv() manipulate the process
 *   environment in a not thread-safe way, and may interfere with getenv()
 *   calls in other threads. Note that getenv() calls may be hidden behind
 *   other APIs. For example, GNU gettext() calls getenv() under the
 *   covers. In general, it is best to treat the environment as readonly.
 *   If you absolutely have to modify the environment, do it early in
 *   main(), when no other threads are around yet.
 *
 * - The setlocale() function changes the locale for the entire process,
 *   affecting all threads. Temporary changes to the locale are often made
 *   to change the behavior of string scanning or formatting functions
 *   like scanf() or printf(). GLib offers a number of string APIs
 *   (like g_ascii_formatd() or g_ascii_strtod()) that can often be
 *   used as an alternative. Or you can use the uselocale() function
 *   to change the locale only for the current thread.
 *
 * - The fork() function only takes the calling thread into the child's
 *   copy of the process image. If other threads were executing in critical
 *   sections they could have left mutexes locked which could easily
 *   cause deadlocks in the new child. For this reason, you should
 *   call exit() or exec() as soon as possible in the child and only
 *   make signal-safe library calls before that.
 *
 * - The daemon() function uses fork() in a way contrary to what is
 *   described above. It should not be used with GLib programs.
 *
 * GLib itself is internally completely thread-safe (all global data is
 * automatically locked), but individual data structure instances are
 * not automatically locked for performance reasons. For example,
 * you must coordinate accesses to the same #GHashTable from multiple
 * threads. The two notable exceptions from this rule are #GMainLoop
 * and #GAsyncQueue, which are thread-safe and need no further
 * application-level locking to be accessed from multiple threads.
 * Most refcounting functions such as g_object_ref() are also thread-safe.
 *
 * A common use for #GThreads is to move a long-running blocking operation out
 * of the main thread and into a worker thread. For GLib functions, such as
 * single GIO operations, this is not necessary, and complicates the code.
 * Instead, the `…_async()` version of the function should be used from the main
 * thread, eliminating the need for locking and synchronisation between multiple
 * threads. If an operation does need to be moved to a worker thread, consider
 * using g_task_run_in_thread(), or a #GThreadPool. #GThreadPool is often a
 * better choice than #GThread, as it handles thread reuse and task queueing;
 * #GTask uses this internally.
 *
 * However, if multiple blocking operations need to be performed in sequence,
 * and it is not possible to use #GTask for them, moving them to a worker thread
 * can clarify the code.
 */

/* G_LOCK Documentation {{{1 ---------------------------------------------- */

/**
 * G_LOCK_DEFINE:
 * @name: the name of the lock
 *
 * The #G_LOCK_ macros provide a convenient interface to #GMutex.
 * #G_LOCK_DEFINE defines a lock. It can appear in any place where
 * variable definitions may appear in programs, i.e. in the first block
 * of a function or outside of functions. The @name parameter will be
 * mangled to get the name of the #GMutex. This means that you
 * can use names of existing variables as the parameter - e.g. the name
 * of the variable you intend to protect with the lock. Look at our
 * give_me_next_number() example using the #G_LOCK macros:
 *
 * Here is an example for using the #G_LOCK convenience macros:
 * |[<!-- language="C" --> 
 *   G_LOCK_DEFINE (current_number);
 *
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *     int ret_val;
 *
 *     G_LOCK (current_number);
 *     ret_val = current_number = calc_next_number (current_number);
 *     G_UNLOCK (current_number);
 *
 *     return ret_val;
 *   }
 * ]|
 */

/**
 * G_LOCK_DEFINE_STATIC:
 * @name: the name of the lock
 *
 * This works like #G_LOCK_DEFINE, but it creates a static object.
 */

/**
 * G_LOCK_EXTERN:
 * @name: the name of the lock
 *
 * This declares a lock, that is defined with #G_LOCK_DEFINE in another
 * module.
 */

/**
 * G_LOCK:
 * @name: the name of the lock
 *
 * Works like g_mutex_lock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 */

/**
 * G_TRYLOCK:
 * @name: the name of the lock
 *
 * Works like g_mutex_trylock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 *
 * Returns: %TRUE, if the lock could be locked.
 */

/**
 * G_UNLOCK:
 * @name: the name of the lock
 *
 * Works like g_mutex_unlock(), but for a lock defined with
 * #G_LOCK_DEFINE.
 */

/* GMutex Documentation {{{1 ------------------------------------------ */

/**
 * GMutex:
 *
 * The #GMutex struct is an opaque data structure to represent a mutex
 * (mutual exclusion). It can be used to protect data against shared
 * access.
 *
 * Take for example the following function:
 * |[<!-- language="C" --> 
 *   int
 *   give_me_next_number (void)
 *   {
 *     static int current_number = 0;
 *
 *     // now do a very complicated calculation to calculate the new
 *     // number, this might for example be a random number generator
 *     current_number = calc_next_number (current_number);
 *
 *     return current_number;
 *   }
 * ]|
 * It is easy to see that this won't work in a multi-threaded
 * application. There current_number must be protected against shared
 * access. A #GMutex can be used as a solution to this problem:
 * |[<!-- language="C" --> 
 *   int
 *   give_me_next_number (void)
 *   {
 *     static GMutex mutex;
 *     static int current_number = 0;
 *     int ret_val;
 *
 *     g_mutex_lock (&mutex);
 *     ret_val = current_number = calc_next_number (current_number);
 *     g_mutex_unlock (&mutex);
 *
 *     return ret_val;
 *   }
 * ]|
 * Notice that the #GMutex is not initialised to any particular value.
 * Its placement in static storage ensures that it will be initialised
 * to all-zeros, which is appropriate.
 *
 * If a #GMutex is placed in other contexts (eg: embedded in a struct)
 * then it must be explicitly initialised using g_mutex_init().
 *
 * A #GMutex should only be accessed via g_mutex_ functions.
 */

/* GRecMutex Documentation {{{1 -------------------------------------- */

/**
 * GRecMutex:
 *
 * The GRecMutex struct is an opaque data structure to represent a
 * recursive mutex. It is similar to a #GMutex with the difference
 * that it is possible to lock a GRecMutex multiple times in the same
 * thread without deadlock. When doing so, care has to be taken to
 * unlock the recursive mutex as often as it has been locked.
 *
 * If a #GRecMutex is allocated in static storage then it can be used
 * without initialisation.  Otherwise, you should call
 * g_rec_mutex_init() on it and g_rec_mutex_clear() when done.
 *
 * A GRecMutex should only be accessed with the
 * g_rec_mutex_ functions.
 *
 * Since: 2.32
 */

/* GRWLock Documentation {{{1 ---------------------------------------- */

/**
 * GRWLock:
 *
 * The GRWLock struct is an opaque data structure to represent a
 * reader-writer lock. It is similar to a #GMutex in that it allows
 * multiple threads to coordinate access to a shared resource.
 *
 * The difference to a mutex is that a reader-writer lock discriminates
 * between read-only ('reader') and full ('writer') access. While only
 * one thread at a time is allowed write access (by holding the 'writer'
 * lock via g_rw_lock_writer_lock()), multiple threads can gain
 * simultaneous read-only access (by holding the 'reader' lock via
 * g_rw_lock_reader_lock()).
 *
 * Here is an example for an array with access functions:
 * |[<!-- language="C" --> 
 *   GRWLock lock;
 *   GPtrArray *array;
 *
 *   gpointer
 *   my_array_get (guint index)
 *   {
 *     gpointer retval = NULL;
 *
 *     if (!array)
 *       return NULL;
 *
 *     g_rw_lock_reader_lock (&lock);
 *     if (index < array->len)
 *       retval = g_ptr_array_index (array, index);
 *     g_rw_lock_reader_unlock (&lock);
 *
 *     return retval;
 *   }
 *
 *   void
 *   my_array_set (guint index, gpointer data)
 *   {
 *     g_rw_lock_writer_lock (&lock);
 *
 *     if (!array)
 *       array = g_ptr_array_new ();
 *
 *     if (index >= array->len)
 *       g_ptr_array_set_size (array, index+1);
 *     g_ptr_array_index (array, index) = data;
 *
 *     g_rw_lock_writer_unlock (&lock);
 *   }
 *  ]|
 * This example shows an array which can be accessed by many readers
 * (the my_array_get() function) simultaneously, whereas the writers
 * (the my_array_set() function) will only be allowed one at a time
 * and only if no readers currently access the array. This is because
 * of the potentially dangerous resizing of the array. Using these
 * functions is fully multi-thread safe now.
 *
 * If a #GRWLock is allocated in static storage then it can be used
 * without initialisation.  Otherwise, you should call
 * g_rw_lock_init() on it and g_rw_lock_clear() when done.
 *
 * A GRWLock should only be accessed with the g_rw_lock_ functions.
 *
 * Since: 2.32
 */

/* GCond Documentation {{{1 ------------------------------------------ */

/**
 * GCond:
 *
 * The #GCond struct is an opaque data structure that represents a
 * condition. Threads can block on a #GCond if they find a certain
 * condition to be false. If other threads change the state of this
 * condition they signal the #GCond, and that causes the waiting
 * threads to be woken up.
 *
 * Consider the following example of a shared variable.  One or more
 * threads can wait for data to be published to the variable and when
 * another thread publishes the data, it can signal one of the waiting
 * threads to wake up to collect the data.
 *
 * Here is an example for using GCond to block a thread until a condition
 * is satisfied:
 * |[<!-- language="C" --> 
 *   gpointer current_data = NULL;
 *   GMutex data_mutex;
 *   GCond data_cond;
 *
 *   void
 *   push_data (gpointer data)
 *   {
 *     g_mutex_lock (&data_mutex);
 *     current_data = data;
 *     g_cond_signal (&data_cond);
 *     g_mutex_unlock (&data_mutex);
 *   }
 *
 *   gpointer
 *   pop_data (void)
 *   {
 *     gpointer data;
 *
 *     g_mutex_lock (&data_mutex);
 *     while (!current_data)
 *       g_cond_wait (&data_cond, &data_mutex);
 *     data = current_data;
 *     current_data = NULL;
 *     g_mutex_unlock (&data_mutex);
 *
 *     return data;
 *   }
 * ]|
 * Whenever a thread calls pop_data() now, it will wait until
 * current_data is non-%NULL, i.e. until some other thread
 * has called push_data().
 *
 * The example shows that use of a condition variable must always be
 * paired with a mutex.  Without the use of a mutex, there would be a
 * race between the check of @current_data by the while loop in
 * pop_data() and waiting. Specifically, another thread could set
 * @current_data after the check, and signal the cond (with nobody
 * waiting on it) before the first thread goes to sleep. #GCond is
 * specifically useful for its ability to release the mutex and go
 * to sleep atomically.
 *
 * It is also important to use the g_cond_wait() and g_cond_wait_until()
 * functions only inside a loop which checks for the condition to be
 * true.  See g_cond_wait() for an explanation of why the condition may
 * not be true even after it returns.
 *
 * If a #GCond is allocated in static storage then it can be used
 * without initialisation.  Otherwise, you should call g_cond_init()
 * on it and g_cond_clear() when done.
 *
 * A #GCond should only be accessed via the g_cond_ functions.
 */

/* GThread Documentation {{{1 ---------------------------------------- */

/**
 * GThread:
 *
 * The #GThread struct represents a running thread. This struct
 * is returned by g_thread_new() or g_thread_try_new(). You can
 * obtain the #GThread struct representing the current thread by
 * calling g_thread_self().
 *
 * GThread is refcounted, see g_thread_ref() and g_thread_unref().
 * The thread represented by it holds a reference while it is running,
 * and g_thread_join() consumes the reference that it is given, so
 * it is normally not necessary to manage GThread references
 * explicitly.
 *
 * The structure is opaque -- none of its fields may be directly
 * accessed.
 */

/**
 * GThreadFunc:
 * @data: data passed to the thread
 *
 * Specifies the type of the @func functions passed to g_thread_new()
 * or g_thread_try_new().
 *
 * Returns: the return value of the thread
 */

/**
 * g_thread_supported:
 *
 * This macro returns %TRUE if the thread system is initialized,
 * and %FALSE if it is not.
 *
 * For language bindings, g_thread_get_initialized() provides
 * the same functionality as a function.
 *
 * Returns: %TRUE, if the thread system is initialized
 */

/* GThreadError {{{1 ------------------------------------------------------- */
/**
 * GThreadError:
 * @G_THREAD_ERROR_AGAIN: a thread couldn't be created due to resource
 *                        shortage. Try again later.
 *
 * Possible errors of thread related functions.
 **/

/**
 * G_THREAD_ERROR:
 *
 * The error domain of the GLib thread subsystem.
 **/
G_DEFINE_QUARK (g_thread_error, g_thread_error)

/* Local Data {{{1 -------------------------------------------------------- */

static GMutex    g_once_mutex;
static GCond     g_once_cond;
static GSList   *g_once_init_list = NULL;

static void g_thread_cleanup (gpointer data);
static GPrivate     g_thread_specific_private = G_PRIVATE_INIT (g_thread_cleanup);

G_LOCK_DEFINE_STATIC (g_thread_new);

/* GOnce {{{1 ------------------------------------------------------------- */

/**
 * GOnce:
 * @status: the status of the #GOnce
 * @retval: the value returned by the call to the function, if @status
 *          is %G_ONCE_STATUS_READY
 *
 * A #GOnce struct controls a one-time initialization function. Any
 * one-time initialization function must have its own unique #GOnce
 * struct.
 *
 * Since: 2.4
 */

/**
 * G_ONCE_INIT:
 *
 * A #GOnce must be initialized with this macro before it can be used.
 *
 * |[<!-- language="C" --> 
 *   GOnce my_once = G_ONCE_INIT;
 * ]|
 *
 * Since: 2.4
 */

/**
 * GOnceStatus:
 * @G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
 * @G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
 * @G_ONCE_STATUS_READY: the function has been called.
 *
 * The possible statuses of a one-time initialization function
 * controlled by a #GOnce struct.
 *
 * Since: 2.4
 */

/**
 * g_once:
 * @once: a #GOnce structure
 * @func: the #GThreadFunc function associated to @once. This function
 *        is called only once, regardless of the number of times it and
 *        its associated #GOnce struct are passed to g_once().
 * @arg: data to be passed to @func
 *
 * The first call to this routine by a process with a given #GOnce
 * struct calls @func with the given argument. Thereafter, subsequent
 * calls to g_once()  with the same #GOnce struct do not call @func
 * again, but return the stored result of the first call. On return
 * from g_once(), the status of @once will be %G_ONCE_STATUS_READY.
 *
 * For example, a mutex or a thread-specific data key must be created
 * exactly once. In a threaded environment, calling g_once() ensures
 * that the initialization is serialized across multiple threads.
 *
 * Calling g_once() recursively on the same #GOnce struct in
 * @func will lead to a deadlock.
 *
 * |[<!-- language="C" --> 
 *   gpointer
 *   get_debug_flags (void)
 *   {
 *     static GOnce my_once = G_ONCE_INIT;
 *
 *     g_once (&my_once, parse_debug_flags, NULL);
 *
 *     return my_once.retval;
 *   }
 * ]|
 *
 * Since: 2.4
 */
gpointer
g_once_impl (GOnce       *once,
	     GThreadFunc  func,
	     gpointer     arg)
{
  g_mutex_lock (&g_once_mutex);

  while (once->status == G_ONCE_STATUS_PROGRESS)
    g_cond_wait (&g_once_cond, &g_once_mutex);

  if (once->status != G_ONCE_STATUS_READY)
    {
      once->status = G_ONCE_STATUS_PROGRESS;
      g_mutex_unlock (&g_once_mutex);

      once->retval = func (arg);

      g_mutex_lock (&g_once_mutex);
      once->status = G_ONCE_STATUS_READY;
      g_cond_broadcast (&g_once_cond);
    }

  g_mutex_unlock (&g_once_mutex);

  return once->retval;
}

/**
 * g_once_init_enter:
 * @location: (not nullable): location of a static initializable variable
 *    containing 0
 *
 * Function to be called when starting a critical initialization
 * section. The argument @location must point to a static
 * 0-initialized variable that will be set to a value other than 0 at
 * the end of the initialization section. In combination with
 * g_once_init_leave() and the unique address @value_location, it can
 * be ensured that an initialization section will be executed only once
 * during a program's life time, and that concurrent threads are
 * blocked until initialization completed. To be used in constructs
 * like this:
 *
 * |[<!-- language="C" --> 
 *   static gsize initialization_value = 0;
 *
 *   if (g_once_init_enter (&initialization_value))
 *     {
 *       gsize setup_value = 42; // initialization code here
 *
 *       g_once_init_leave (&initialization_value, setup_value);
 *     }
 *
 *   // use initialization_value here
 * ]|
 *
 * Returns: %TRUE if the initialization section should be entered,
 *     %FALSE and blocks otherwise
 *
 * Since: 2.14
 */
gboolean
(g_once_init_enter) (volatile void *location)
{
  volatile gsize *value_location = location;
  gboolean need_init = FALSE;
  g_mutex_lock (&g_once_mutex);
  if (g_atomic_pointer_get (value_location) == NULL)
    {
      if (!g_slist_find (g_once_init_list, (void*) value_location))
        {
          need_init = TRUE;
          g_once_init_list = g_slist_prepend (g_once_init_list, (void*) value_location);
        }
      else
        do
          g_cond_wait (&g_once_cond, &g_once_mutex);
        while (g_slist_find (g_once_init_list, (void*) value_location));
    }
  g_mutex_unlock (&g_once_mutex);
  return need_init;
}

/**
 * g_once_init_leave:
 * @location: (not nullable): location of a static initializable variable
 *    containing 0
 * @result: new non-0 value for *@value_location
 *
 * Counterpart to g_once_init_enter(). Expects a location of a static
 * 0-initialized initialization variable, and an initialization value
 * other than 0. Sets the variable to the initialization value, and
 * releases concurrent threads blocking in g_once_init_enter() on this
 * initialization variable.
 *
 * Since: 2.14
 */
void
(g_once_init_leave) (volatile void *location,
                     gsize          result)
{
  volatile gsize *value_location = location;

  g_return_if_fail (g_atomic_pointer_get (value_location) == NULL);
  g_return_if_fail (result != 0);
  g_return_if_fail (g_once_init_list != NULL);

  g_atomic_pointer_set (value_location, result);
  g_mutex_lock (&g_once_mutex);
  g_once_init_list = g_slist_remove (g_once_init_list, (void*) value_location);
  g_cond_broadcast (&g_once_cond);
  g_mutex_unlock (&g_once_mutex);
}

/* GThread {{{1 -------------------------------------------------------- */

/**
 * g_thread_ref:
 * @thread: a #GThread
 *
 * Increase the reference count on @thread.
 *
 * Returns: a new reference to @thread
 *
 * Since: 2.32
 */
GThread *
g_thread_ref (GThread *thread)
{
  GRealThread *real = (GRealThread *) thread;

  g_atomic_int_inc (&real->ref_count);

  return thread;
}

/**
 * g_thread_unref:
 * @thread: a #GThread
 *
 * Decrease the reference count on @thread, possibly freeing all
 * resources associated with it.
 *
 * Note that each thread holds a reference to its #GThread while
 * it is running, so it is safe to drop your own reference to it
 * if you don't need it anymore.
 *
 * Since: 2.32
 */
void
g_thread_unref (GThread *thread)
{
  GRealThread *real = (GRealThread *) thread;

  if (g_atomic_int_dec_and_test (&real->ref_count))
    {
      if (real->ours)
        g_system_thread_free (real);
      else
        g_slice_free (GRealThread, real);
    }
}

static void
g_thread_cleanup (gpointer data)
{
  g_thread_unref (data);
}

gpointer
g_thread_proxy (gpointer data)
{
  GRealThread* thread = data;

  g_assert (data);

  /* This has to happen before G_LOCK, as that might call g_thread_self */
  g_private_set (&g_thread_specific_private, data);

  /* The lock makes sure that g_thread_new_internal() has a chance to
   * setup 'func' and 'data' before we make the call.
   */
  G_LOCK (g_thread_new);
  G_UNLOCK (g_thread_new);

  TRACE (GLIB_THREAD_SPAWNED (thread->thread.func, thread->thread.data,
                              thread->name));

  if (thread->name)
    {
      g_system_thread_set_name (thread->name);
      g_free (thread->name);
      thread->name = NULL;
    }

  thread->retval = thread->thread.func (thread->thread.data);

  return NULL;
}

/**
 * g_thread_new:
 * @name: (nullable): an (optional) name for the new thread
 * @func: a function to execute in the new thread
 * @data: an argument to supply to the new thread
 *
 * This function creates a new thread. The new thread starts by invoking
 * @func with the argument data. The thread will run until @func returns
 * or until g_thread_exit() is called from the new thread. The return value
 * of @func becomes the return value of the thread, which can be obtained
 * with g_thread_join().
 *
 * The @name can be useful for discriminating threads in a debugger.
 * It is not used for other purposes and does not have to be unique.
 * Some systems restrict the length of @name to 16 bytes.
 *
 * If the thread can not be created the program aborts. See
 * g_thread_try_new() if you want to attempt to deal with failures.
 *
 * If you are using threads to offload (potentially many) short-lived tasks,
 * #GThreadPool may be more appropriate than manually spawning and tracking
 * multiple #GThreads.
 *
 * To free the struct returned by this function, use g_thread_unref().
 * Note that g_thread_join() implicitly unrefs the #GThread as well.
 *
 * Returns: the new #GThread
 *
 * Since: 2.32
 */
GThread *
g_thread_new (const gchar *name,
              GThreadFunc  func,
              gpointer     data)
{
  GError *error = NULL;
  GThread *thread;

  thread = g_thread_new_internal (name, g_thread_proxy, func, data, 0, &error);

  if G_UNLIKELY (thread == NULL)
    g_error ("creating thread '%s': %s", name ? name : "", error->message);

  return thread;
}

/**
 * g_thread_try_new:
 * @name: (nullable): an (optional) name for the new thread
 * @func: a function to execute in the new thread
 * @data: an argument to supply to the new thread
 * @error: return location for error, or %NULL
 *
 * This function is the same as g_thread_new() except that
 * it allows for the possibility of failure.
 *
 * If a thread can not be created (due to resource limits),
 * @error is set and %NULL is returned.
 *
 * Returns: the new #GThread, or %NULL if an error occurred
 *
 * Since: 2.32
 */
GThread *
g_thread_try_new (const gchar  *name,
                  GThreadFunc   func,
                  gpointer      data,
                  GError      **error)
{
  return g_thread_new_internal (name, g_thread_proxy, func, data, 0, error);
}

GThread *
g_thread_new_internal (const gchar   *name,
                       GThreadFunc    proxy,
                       GThreadFunc    func,
                       gpointer       data,
                       gsize          stack_size,
                       GError       **error)
{
  GRealThread *thread;

  g_return_val_if_fail (func != NULL, NULL);

  G_LOCK (g_thread_new);
  thread = g_system_thread_new (proxy, stack_size, error);
  if (thread)
    {
      thread->ref_count = 2;
      thread->ours = TRUE;
      thread->thread.joinable = TRUE;
      thread->thread.func = func;
      thread->thread.data = data;
      thread->name = g_strdup (name);
    }
  G_UNLOCK (g_thread_new);

  return (GThread*) thread;
}

/**
 * g_thread_exit:
 * @retval: the return value of this thread
 *
 * Terminates the current thread.
 *
 * If another thread is waiting for us using g_thread_join() then the
 * waiting thread will be woken up and get @retval as the return value
 * of g_thread_join().
 *
 * Calling g_thread_exit() with a parameter @retval is equivalent to
 * returning @retval from the function @func, as given to g_thread_new().
 *
 * You must only call g_thread_exit() from a thread that you created
 * yourself with g_thread_new() or related APIs. You must not call
 * this function from a thread created with another threading library
 * or or from within a #GThreadPool.
 */
void
g_thread_exit (gpointer retval)
{
  GRealThread* real = (GRealThread*) g_thread_self ();

  if G_UNLIKELY (!real->ours)
    g_error ("attempt to g_thread_exit() a thread not created by GLib");

  real->retval = retval;

  g_system_thread_exit ();
}

/**
 * g_thread_join:
 * @thread: a #GThread
 *
 * Waits until @thread finishes, i.e. the function @func, as
 * given to g_thread_new(), returns or g_thread_exit() is called.
 * If @thread has already terminated, then g_thread_join()
 * returns immediately.
 *
 * Any thread can wait for any other thread by calling g_thread_join(),
 * not just its 'creator'. Calling g_thread_join() from multiple threads
 * for the same @thread leads to undefined behaviour.
 *
 * The value returned by @func or given to g_thread_exit() is
 * returned by this function.
 *
 * g_thread_join() consumes the reference to the passed-in @thread.
 * This will usually cause the #GThread struct and associated resources
 * to be freed. Use g_thread_ref() to obtain an extra reference if you
 * want to keep the GThread alive beyond the g_thread_join() call.
 *
 * Returns: the return value of the thread
 */
gpointer
g_thread_join (GThread *thread)
{
  GRealThread *real = (GRealThread*) thread;
  gpointer retval;

  g_return_val_if_fail (thread, NULL);
  g_return_val_if_fail (real->ours, NULL);

  g_system_thread_wait (real);

  retval = real->retval;

  /* Just to make sure, this isn't used any more */
  thread->joinable = 0;

  g_thread_unref (thread);

  return retval;
}

/**
 * g_thread_self:
 *
 * This function returns the #GThread corresponding to the
 * current thread. Note that this function does not increase
 * the reference count of the returned struct.
 *
 * This function will return a #GThread even for threads that
 * were not created by GLib (i.e. those created by other threading
 * APIs). This may be useful for thread identification purposes
 * (i.e. comparisons) but you must not use GLib functions (such
 * as g_thread_join()) on these threads.
 *
 * Returns: the #GThread representing the current thread
 */
GThread*
g_thread_self (void)
{
  GRealThread* thread = g_private_get (&g_thread_specific_private);

  if (!thread)
    {
      /* If no thread data is available, provide and set one.
       * This can happen for the main thread and for threads
       * that are not created by GLib.
       */
      thread = g_slice_new0 (GRealThread);
      thread->ref_count = 1;

      g_private_set (&g_thread_specific_private, thread);
    }

  return (GThread*) thread;
}

/**
 * g_get_num_processors:
 *
 * Determine the approximate number of threads that the system will
 * schedule simultaneously for this process.  This is intended to be
 * used as a parameter to g_thread_pool_new() for CPU bound tasks and
 * similar cases.
 *
 * Returns: Number of schedulable threads, always greater than 0
 *
 * Since: 2.36
 */
guint
g_get_num_processors (void)
{
#ifdef G_OS_WIN32
  unsigned int count;
  SYSTEM_INFO sysinfo;
  DWORD_PTR process_cpus;
  DWORD_PTR system_cpus;

  /* This *never* fails, use it as fallback */
  GetNativeSystemInfo (&sysinfo);
  count = (int) sysinfo.dwNumberOfProcessors;

  if (GetProcessAffinityMask (GetCurrentProcess (),
                              &process_cpus, &system_cpus))
    {
      unsigned int af_count;

      for (af_count = 0; process_cpus != 0; process_cpus >>= 1)
        if (process_cpus & 1)
          af_count++;

      /* Prefer affinity-based result, if available */
      if (af_count > 0)
        count = af_count;
    }

  if (count > 0)
    return count;
#elif defined(_SC_NPROCESSORS_ONLN)
  {
    int count;

    count = sysconf (_SC_NPROCESSORS_ONLN);
    if (count > 0)
      return count;
  }
#elif defined HW_NCPU
  {
    int mib[2], count = 0;
    size_t len;

    mib[0] = CTL_HW;
    mib[1] = HW_NCPU;
    len = sizeof(count);

    if (sysctl (mib, 2, &count, &len, NULL, 0) == 0 && count > 0)
      return count;
  }
#endif

  return 1; /* Fallback */
}

/* Epilogue {{{1 */
/* vim: set foldmethod=marker: */