1 /* GLIB - Library of useful routines for C programming
2 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
3 *
4 * gthread.c: MT safety related functions
5 * Copyright 1998 Sebastian Wilhelmi; University of Karlsruhe
6 * Owen Taylor
7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
20 */
21
22 /* Prelude {{{1 ----------------------------------------------------------- */
23
24 /*
25 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
26 * file for a list of people on the GLib Team. See the ChangeLog
27 * files for a list of changes. These files are distributed with
28 * GLib at ftp://ftp.gtk.org/pub/gtk/.
29 */
30
31 /*
32 * MT safe
33 */
34
35 /* implement gthread.h's inline functions */
36 #define G_IMPLEMENT_INLINES 1
37 #define __G_THREAD_C__
38
39 #include "config.h"
40
41 #include "gthread.h"
42 #include "gthreadprivate.h"
43
44 #include <string.h>
45
46 #ifdef G_OS_UNIX
47 #include <unistd.h>
48 #endif
49
50 #ifndef G_OS_WIN32
51 #include <sys/time.h>
52 #include <time.h>
53 #else
54 #include <windows.h>
55 #endif /* G_OS_WIN32 */
56
57 #include "gslice.h"
58 #include "gstrfuncs.h"
59 #include "gtestutils.h"
60 #include "glib_trace.h"
61
62 /**
63 * SECTION:threads
64 * @title: Threads
65 * @short_description: portable support for threads, mutexes, locks,
66 * conditions and thread private data
67 * @see_also: #GThreadPool, #GAsyncQueue
68 *
69 * Threads act almost like processes, but unlike processes all threads
70 * of one process share the same memory. This is good, as it provides
71 * easy communication between the involved threads via this shared
72 * memory, and it is bad, because strange things (so called
73 * "Heisenbugs") might happen if the program is not carefully designed.
74 * In particular, due to the concurrent nature of threads, no
75 * assumptions on the order of execution of code running in different
76 * threads can be made, unless order is explicitly forced by the
77 * programmer through synchronization primitives.
78 *
79 * The aim of the thread-related functions in GLib is to provide a
80 * portable means for writing multi-threaded software. There are
81 * primitives for mutexes to protect the access to portions of memory
82 * (#GMutex, #GRecMutex and #GRWLock). There is a facility to use
83 * individual bits for locks (g_bit_lock()). There are primitives
84 * for condition variables to allow synchronization of threads (#GCond).
85 * There are primitives for thread-private data - data that every
86 * thread has a private instance of (#GPrivate). There are facilities
87 * for one-time initialization (#GOnce, g_once_init_enter()). Finally,
88 * there are primitives to create and manage threads (#GThread).
89 *
90 * The GLib threading system used to be initialized with g_thread_init().
91 * This is no longer necessary. Since version 2.32, the GLib threading
92 * system is automatically initialized at the start of your program,
93 * and all thread-creation functions and synchronization primitives
94 * are available right away.
95 *
96 * Note that it is not safe to assume that your program has no threads
97 * even if you don't call g_thread_new() yourself. GLib and GIO can
98 * and will create threads for their own purposes in some cases, such
99 * as when using g_unix_signal_source_new() or when using GDBus.
100 *
101 * Originally, UNIX did not have threads, and therefore some traditional
102 * UNIX APIs are problematic in threaded programs. Some notable examples
103 * are
104 *
105 * - C library functions that return data in statically allocated
106 * buffers, such as strtok() or strerror(). For many of these,
107 * there are thread-safe variants with a _r suffix, or you can
108 * look at corresponding GLib APIs (like g_strsplit() or g_strerror()).
109 *
110 * - The functions setenv() and unsetenv() manipulate the process
111 * environment in a not thread-safe way, and may interfere with getenv()
112 * calls in other threads. Note that getenv() calls may be hidden behind
113 * other APIs. For example, GNU gettext() calls getenv() under the
114 * covers. In general, it is best to treat the environment as readonly.
115 * If you absolutely have to modify the environment, do it early in
116 * main(), when no other threads are around yet.
117 *
118 * - The setlocale() function changes the locale for the entire process,
119 * affecting all threads. Temporary changes to the locale are often made
120 * to change the behavior of string scanning or formatting functions
121 * like scanf() or printf(). GLib offers a number of string APIs
122 * (like g_ascii_formatd() or g_ascii_strtod()) that can often be
123 * used as an alternative. Or you can use the uselocale() function
124 * to change the locale only for the current thread.
125 *
126 * - The fork() function only takes the calling thread into the child's
127 * copy of the process image. If other threads were executing in critical
128 * sections they could have left mutexes locked which could easily
129 * cause deadlocks in the new child. For this reason, you should
130 * call exit() or exec() as soon as possible in the child and only
131 * make signal-safe library calls before that.
132 *
133 * - The daemon() function uses fork() in a way contrary to what is
134 * described above. It should not be used with GLib programs.
135 *
136 * GLib itself is internally completely thread-safe (all global data is
137 * automatically locked), but individual data structure instances are
138 * not automatically locked for performance reasons. For example,
139 * you must coordinate accesses to the same #GHashTable from multiple
140 * threads. The two notable exceptions from this rule are #GMainLoop
141 * and #GAsyncQueue, which are thread-safe and need no further
142 * application-level locking to be accessed from multiple threads.
143 * Most refcounting functions such as g_object_ref() are also thread-safe.
144 *
145 * A common use for #GThreads is to move a long-running blocking operation out
146 * of the main thread and into a worker thread. For GLib functions, such as
147 * single GIO operations, this is not necessary, and complicates the code.
148 * Instead, the `…_async()` version of the function should be used from the main
149 * thread, eliminating the need for locking and synchronisation between multiple
150 * threads. If an operation does need to be moved to a worker thread, consider
151 * using g_task_run_in_thread(), or a #GThreadPool. #GThreadPool is often a
152 * better choice than #GThread, as it handles thread reuse and task queueing;
153 * #GTask uses this internally.
154 *
155 * However, if multiple blocking operations need to be performed in sequence,
156 * and it is not possible to use #GTask for them, moving them to a worker thread
157 * can clarify the code.
158 */
159
160 /* G_LOCK Documentation {{{1 ---------------------------------------------- */
161
162 /**
163 * G_LOCK_DEFINE:
164 * @name: the name of the lock
165 *
166 * The #G_LOCK_ macros provide a convenient interface to #GMutex.
167 * #G_LOCK_DEFINE defines a lock. It can appear in any place where
168 * variable definitions may appear in programs, i.e. in the first block
169 * of a function or outside of functions. The @name parameter will be
170 * mangled to get the name of the #GMutex. This means that you
171 * can use names of existing variables as the parameter - e.g. the name
172 * of the variable you intend to protect with the lock. Look at our
173 * give_me_next_number() example using the #G_LOCK macros:
174 *
175 * Here is an example for using the #G_LOCK convenience macros:
176 * |[<!-- language="C" -->
177 * G_LOCK_DEFINE (current_number);
178 *
179 * int
180 * give_me_next_number (void)
181 * {
182 * static int current_number = 0;
183 * int ret_val;
184 *
185 * G_LOCK (current_number);
186 * ret_val = current_number = calc_next_number (current_number);
187 * G_UNLOCK (current_number);
188 *
189 * return ret_val;
190 * }
191 * ]|
192 */
193
194 /**
195 * G_LOCK_DEFINE_STATIC:
196 * @name: the name of the lock
197 *
198 * This works like #G_LOCK_DEFINE, but it creates a static object.
199 */
200
201 /**
202 * G_LOCK_EXTERN:
203 * @name: the name of the lock
204 *
205 * This declares a lock, that is defined with #G_LOCK_DEFINE in another
206 * module.
207 */
208
209 /**
210 * G_LOCK:
211 * @name: the name of the lock
212 *
213 * Works like g_mutex_lock(), but for a lock defined with
214 * #G_LOCK_DEFINE.
215 */
216
217 /**
218 * G_TRYLOCK:
219 * @name: the name of the lock
220 *
221 * Works like g_mutex_trylock(), but for a lock defined with
222 * #G_LOCK_DEFINE.
223 *
224 * Returns: %TRUE, if the lock could be locked.
225 */
226
227 /**
228 * G_UNLOCK:
229 * @name: the name of the lock
230 *
231 * Works like g_mutex_unlock(), but for a lock defined with
232 * #G_LOCK_DEFINE.
233 */
234
235 /* GMutex Documentation {{{1 ------------------------------------------ */
236
237 /**
238 * GMutex:
239 *
240 * The #GMutex struct is an opaque data structure to represent a mutex
241 * (mutual exclusion). It can be used to protect data against shared
242 * access.
243 *
244 * Take for example the following function:
245 * |[<!-- language="C" -->
246 * int
247 * give_me_next_number (void)
248 * {
249 * static int current_number = 0;
250 *
251 * // now do a very complicated calculation to calculate the new
252 * // number, this might for example be a random number generator
253 * current_number = calc_next_number (current_number);
254 *
255 * return current_number;
256 * }
257 * ]|
258 * It is easy to see that this won't work in a multi-threaded
259 * application. There current_number must be protected against shared
260 * access. A #GMutex can be used as a solution to this problem:
261 * |[<!-- language="C" -->
262 * int
263 * give_me_next_number (void)
264 * {
265 * static GMutex mutex;
266 * static int current_number = 0;
267 * int ret_val;
268 *
269 * g_mutex_lock (&mutex);
270 * ret_val = current_number = calc_next_number (current_number);
271 * g_mutex_unlock (&mutex);
272 *
273 * return ret_val;
274 * }
275 * ]|
276 * Notice that the #GMutex is not initialised to any particular value.
277 * Its placement in static storage ensures that it will be initialised
278 * to all-zeros, which is appropriate.
279 *
280 * If a #GMutex is placed in other contexts (eg: embedded in a struct)
281 * then it must be explicitly initialised using g_mutex_init().
282 *
283 * A #GMutex should only be accessed via g_mutex_ functions.
284 */
285
286 /* GRecMutex Documentation {{{1 -------------------------------------- */
287
288 /**
289 * GRecMutex:
290 *
291 * The GRecMutex struct is an opaque data structure to represent a
292 * recursive mutex. It is similar to a #GMutex with the difference
293 * that it is possible to lock a GRecMutex multiple times in the same
294 * thread without deadlock. When doing so, care has to be taken to
295 * unlock the recursive mutex as often as it has been locked.
296 *
297 * If a #GRecMutex is allocated in static storage then it can be used
298 * without initialisation. Otherwise, you should call
299 * g_rec_mutex_init() on it and g_rec_mutex_clear() when done.
300 *
301 * A GRecMutex should only be accessed with the
302 * g_rec_mutex_ functions.
303 *
304 * Since: 2.32
305 */
306
307 /* GRWLock Documentation {{{1 ---------------------------------------- */
308
309 /**
310 * GRWLock:
311 *
312 * The GRWLock struct is an opaque data structure to represent a
313 * reader-writer lock. It is similar to a #GMutex in that it allows
314 * multiple threads to coordinate access to a shared resource.
315 *
316 * The difference to a mutex is that a reader-writer lock discriminates
317 * between read-only ('reader') and full ('writer') access. While only
318 * one thread at a time is allowed write access (by holding the 'writer'
319 * lock via g_rw_lock_writer_lock()), multiple threads can gain
320 * simultaneous read-only access (by holding the 'reader' lock via
321 * g_rw_lock_reader_lock()).
322 *
323 * It is unspecified whether readers or writers have priority in acquiring the
324 * lock when a reader already holds the lock and a writer is queued to acquire
325 * it.
326 *
327 * Here is an example for an array with access functions:
328 * |[<!-- language="C" -->
329 * GRWLock lock;
330 * GPtrArray *array;
331 *
332 * gpointer
333 * my_array_get (guint index)
334 * {
335 * gpointer retval = NULL;
336 *
337 * if (!array)
338 * return NULL;
339 *
340 * g_rw_lock_reader_lock (&lock);
341 * if (index < array->len)
342 * retval = g_ptr_array_index (array, index);
343 * g_rw_lock_reader_unlock (&lock);
344 *
345 * return retval;
346 * }
347 *
348 * void
349 * my_array_set (guint index, gpointer data)
350 * {
351 * g_rw_lock_writer_lock (&lock);
352 *
353 * if (!array)
354 * array = g_ptr_array_new ();
355 *
356 * if (index >= array->len)
357 * g_ptr_array_set_size (array, index+1);
358 * g_ptr_array_index (array, index) = data;
359 *
360 * g_rw_lock_writer_unlock (&lock);
361 * }
362 * ]|
363 * This example shows an array which can be accessed by many readers
364 * (the my_array_get() function) simultaneously, whereas the writers
365 * (the my_array_set() function) will only be allowed one at a time
366 * and only if no readers currently access the array. This is because
367 * of the potentially dangerous resizing of the array. Using these
368 * functions is fully multi-thread safe now.
369 *
370 * If a #GRWLock is allocated in static storage then it can be used
371 * without initialisation. Otherwise, you should call
372 * g_rw_lock_init() on it and g_rw_lock_clear() when done.
373 *
374 * A GRWLock should only be accessed with the g_rw_lock_ functions.
375 *
376 * Since: 2.32
377 */
378
379 /* GCond Documentation {{{1 ------------------------------------------ */
380
381 /**
382 * GCond:
383 *
384 * The #GCond struct is an opaque data structure that represents a
385 * condition. Threads can block on a #GCond if they find a certain
386 * condition to be false. If other threads change the state of this
387 * condition they signal the #GCond, and that causes the waiting
388 * threads to be woken up.
389 *
390 * Consider the following example of a shared variable. One or more
391 * threads can wait for data to be published to the variable and when
392 * another thread publishes the data, it can signal one of the waiting
393 * threads to wake up to collect the data.
394 *
395 * Here is an example for using GCond to block a thread until a condition
396 * is satisfied:
397 * |[<!-- language="C" -->
398 * gpointer current_data = NULL;
399 * GMutex data_mutex;
400 * GCond data_cond;
401 *
402 * void
403 * push_data (gpointer data)
404 * {
405 * g_mutex_lock (&data_mutex);
406 * current_data = data;
407 * g_cond_signal (&data_cond);
408 * g_mutex_unlock (&data_mutex);
409 * }
410 *
411 * gpointer
412 * pop_data (void)
413 * {
414 * gpointer data;
415 *
416 * g_mutex_lock (&data_mutex);
417 * while (!current_data)
418 * g_cond_wait (&data_cond, &data_mutex);
419 * data = current_data;
420 * current_data = NULL;
421 * g_mutex_unlock (&data_mutex);
422 *
423 * return data;
424 * }
425 * ]|
426 * Whenever a thread calls pop_data() now, it will wait until
427 * current_data is non-%NULL, i.e. until some other thread
428 * has called push_data().
429 *
430 * The example shows that use of a condition variable must always be
431 * paired with a mutex. Without the use of a mutex, there would be a
432 * race between the check of @current_data by the while loop in
433 * pop_data() and waiting. Specifically, another thread could set
434 * @current_data after the check, and signal the cond (with nobody
435 * waiting on it) before the first thread goes to sleep. #GCond is
436 * specifically useful for its ability to release the mutex and go
437 * to sleep atomically.
438 *
439 * It is also important to use the g_cond_wait() and g_cond_wait_until()
440 * functions only inside a loop which checks for the condition to be
441 * true. See g_cond_wait() for an explanation of why the condition may
442 * not be true even after it returns.
443 *
444 * If a #GCond is allocated in static storage then it can be used
445 * without initialisation. Otherwise, you should call g_cond_init()
446 * on it and g_cond_clear() when done.
447 *
448 * A #GCond should only be accessed via the g_cond_ functions.
449 */
450
451 /* GThread Documentation {{{1 ---------------------------------------- */
452
453 /**
454 * GThread:
455 *
456 * The #GThread struct represents a running thread. This struct
457 * is returned by g_thread_new() or g_thread_try_new(). You can
458 * obtain the #GThread struct representing the current thread by
459 * calling g_thread_self().
460 *
461 * GThread is refcounted, see g_thread_ref() and g_thread_unref().
462 * The thread represented by it holds a reference while it is running,
463 * and g_thread_join() consumes the reference that it is given, so
464 * it is normally not necessary to manage GThread references
465 * explicitly.
466 *
467 * The structure is opaque -- none of its fields may be directly
468 * accessed.
469 */
470
471 /**
472 * GThreadFunc:
473 * @data: data passed to the thread
474 *
475 * Specifies the type of the @func functions passed to g_thread_new()
476 * or g_thread_try_new().
477 *
478 * Returns: the return value of the thread
479 */
480
481 /**
482 * g_thread_supported:
483 *
484 * This macro returns %TRUE if the thread system is initialized,
485 * and %FALSE if it is not.
486 *
487 * For language bindings, g_thread_get_initialized() provides
488 * the same functionality as a function.
489 *
490 * Returns: %TRUE, if the thread system is initialized
491 */
492
493 /* GThreadError {{{1 ------------------------------------------------------- */
494 /**
495 * GThreadError:
496 * @G_THREAD_ERROR_AGAIN: a thread couldn't be created due to resource
497 * shortage. Try again later.
498 *
499 * Possible errors of thread related functions.
500 **/
501
502 /**
503 * G_THREAD_ERROR:
504 *
505 * The error domain of the GLib thread subsystem.
506 **/
507 G_DEFINE_QUARK (g_thread_error, g_thread_error)
508
509 /* Local Data {{{1 -------------------------------------------------------- */
510
511 static GMutex g_once_mutex;
512 static GCond g_once_cond;
513 static GSList *g_once_init_list = NULL;
514
515 static void g_thread_cleanup (gpointer data);
516 static GPrivate g_thread_specific_private = G_PRIVATE_INIT (g_thread_cleanup);
517
518 /*
519 * g_private_set_alloc0:
520 * @key: a #GPrivate
521 * @size: size of the allocation, in bytes
522 *
523 * Sets the thread local variable @key to have a newly-allocated and zero-filled
524 * value of given @size, and returns a pointer to that memory. Allocations made
525 * using this API will be suppressed in valgrind: it is intended to be used for
526 * one-time allocations which are known to be leaked, such as those for
527 * per-thread initialisation data. Otherwise, this function behaves the same as
528 * g_private_set().
529 *
530 * Returns: (transfer full): new thread-local heap allocation of size @size
531 * Since: 2.60
532 */
533 /*< private >*/
534 gpointer
g_private_set_alloc0(GPrivate * key,gsize size)535 g_private_set_alloc0 (GPrivate *key,
536 gsize size)
537 {
538 gpointer allocated = g_malloc0 (size);
539
540 g_private_set (key, allocated);
541
542 return g_steal_pointer (&allocated);
543 }
544
545 /* GOnce {{{1 ------------------------------------------------------------- */
546
547 /**
548 * GOnce:
549 * @status: the status of the #GOnce
550 * @retval: the value returned by the call to the function, if @status
551 * is %G_ONCE_STATUS_READY
552 *
553 * A #GOnce struct controls a one-time initialization function. Any
554 * one-time initialization function must have its own unique #GOnce
555 * struct.
556 *
557 * Since: 2.4
558 */
559
560 /**
561 * G_ONCE_INIT:
562 *
563 * A #GOnce must be initialized with this macro before it can be used.
564 *
565 * |[<!-- language="C" -->
566 * GOnce my_once = G_ONCE_INIT;
567 * ]|
568 *
569 * Since: 2.4
570 */
571
572 /**
573 * GOnceStatus:
574 * @G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
575 * @G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
576 * @G_ONCE_STATUS_READY: the function has been called.
577 *
578 * The possible statuses of a one-time initialization function
579 * controlled by a #GOnce struct.
580 *
581 * Since: 2.4
582 */
583
584 /**
585 * g_once:
586 * @once: a #GOnce structure
587 * @func: the #GThreadFunc function associated to @once. This function
588 * is called only once, regardless of the number of times it and
589 * its associated #GOnce struct are passed to g_once().
590 * @arg: data to be passed to @func
591 *
592 * The first call to this routine by a process with a given #GOnce
593 * struct calls @func with the given argument. Thereafter, subsequent
594 * calls to g_once() with the same #GOnce struct do not call @func
595 * again, but return the stored result of the first call. On return
596 * from g_once(), the status of @once will be %G_ONCE_STATUS_READY.
597 *
598 * For example, a mutex or a thread-specific data key must be created
599 * exactly once. In a threaded environment, calling g_once() ensures
600 * that the initialization is serialized across multiple threads.
601 *
602 * Calling g_once() recursively on the same #GOnce struct in
603 * @func will lead to a deadlock.
604 *
605 * |[<!-- language="C" -->
606 * gpointer
607 * get_debug_flags (void)
608 * {
609 * static GOnce my_once = G_ONCE_INIT;
610 *
611 * g_once (&my_once, parse_debug_flags, NULL);
612 *
613 * return my_once.retval;
614 * }
615 * ]|
616 *
617 * Since: 2.4
618 */
619 gpointer
g_once_impl(GOnce * once,GThreadFunc func,gpointer arg)620 g_once_impl (GOnce *once,
621 GThreadFunc func,
622 gpointer arg)
623 {
624 g_mutex_lock (&g_once_mutex);
625
626 while (once->status == G_ONCE_STATUS_PROGRESS)
627 g_cond_wait (&g_once_cond, &g_once_mutex);
628
629 if (once->status != G_ONCE_STATUS_READY)
630 {
631 once->status = G_ONCE_STATUS_PROGRESS;
632 g_mutex_unlock (&g_once_mutex);
633
634 once->retval = func (arg);
635
636 g_mutex_lock (&g_once_mutex);
637 once->status = G_ONCE_STATUS_READY;
638 g_cond_broadcast (&g_once_cond);
639 }
640
641 g_mutex_unlock (&g_once_mutex);
642
643 return once->retval;
644 }
645
646 /**
647 * g_once_init_enter:
648 * @location: (not nullable): location of a static initializable variable
649 * containing 0
650 *
651 * Function to be called when starting a critical initialization
652 * section. The argument @location must point to a static
653 * 0-initialized variable that will be set to a value other than 0 at
654 * the end of the initialization section. In combination with
655 * g_once_init_leave() and the unique address @value_location, it can
656 * be ensured that an initialization section will be executed only once
657 * during a program's life time, and that concurrent threads are
658 * blocked until initialization completed. To be used in constructs
659 * like this:
660 *
661 * |[<!-- language="C" -->
662 * static gsize initialization_value = 0;
663 *
664 * if (g_once_init_enter (&initialization_value))
665 * {
666 * gsize setup_value = 42; // initialization code here
667 *
668 * g_once_init_leave (&initialization_value, setup_value);
669 * }
670 *
671 * // use initialization_value here
672 * ]|
673 *
674 * Returns: %TRUE if the initialization section should be entered,
675 * %FALSE and blocks otherwise
676 *
677 * Since: 2.14
678 */
gboolean(g_once_init_enter)679 gboolean
680 (g_once_init_enter) (volatile void *location)
681 {
682 volatile gsize *value_location = location;
683 gboolean need_init = FALSE;
684 g_mutex_lock (&g_once_mutex);
685 if (g_atomic_pointer_get (value_location) == NULL)
686 {
687 if (!g_slist_find (g_once_init_list, (void*) value_location))
688 {
689 need_init = TRUE;
690 g_once_init_list = g_slist_prepend (g_once_init_list, (void*) value_location);
691 }
692 else
693 do
694 g_cond_wait (&g_once_cond, &g_once_mutex);
695 while (g_slist_find (g_once_init_list, (void*) value_location));
696 }
697 g_mutex_unlock (&g_once_mutex);
698 return need_init;
699 }
700
701 /**
702 * g_once_init_leave:
703 * @location: (not nullable): location of a static initializable variable
704 * containing 0
705 * @result: new non-0 value for *@value_location
706 *
707 * Counterpart to g_once_init_enter(). Expects a location of a static
708 * 0-initialized initialization variable, and an initialization value
709 * other than 0. Sets the variable to the initialization value, and
710 * releases concurrent threads blocking in g_once_init_enter() on this
711 * initialization variable.
712 *
713 * Since: 2.14
714 */
715 void
716 (g_once_init_leave) (volatile void *location,
717 gsize result)
718 {
719 volatile gsize *value_location = location;
720
721 g_return_if_fail (g_atomic_pointer_get (value_location) == NULL);
722 g_return_if_fail (result != 0);
723
724 g_atomic_pointer_set (value_location, result);
725 g_mutex_lock (&g_once_mutex);
726 g_return_if_fail (g_once_init_list != NULL);
727 g_once_init_list = g_slist_remove (g_once_init_list, (void*) value_location);
728 g_cond_broadcast (&g_once_cond);
729 g_mutex_unlock (&g_once_mutex);
730 }
731
732 /* GThread {{{1 -------------------------------------------------------- */
733
734 /**
735 * g_thread_ref:
736 * @thread: a #GThread
737 *
738 * Increase the reference count on @thread.
739 *
740 * Returns: a new reference to @thread
741 *
742 * Since: 2.32
743 */
744 GThread *
g_thread_ref(GThread * thread)745 g_thread_ref (GThread *thread)
746 {
747 GRealThread *real = (GRealThread *) thread;
748
749 g_atomic_int_inc (&real->ref_count);
750
751 return thread;
752 }
753
754 /**
755 * g_thread_unref:
756 * @thread: a #GThread
757 *
758 * Decrease the reference count on @thread, possibly freeing all
759 * resources associated with it.
760 *
761 * Note that each thread holds a reference to its #GThread while
762 * it is running, so it is safe to drop your own reference to it
763 * if you don't need it anymore.
764 *
765 * Since: 2.32
766 */
767 void
g_thread_unref(GThread * thread)768 g_thread_unref (GThread *thread)
769 {
770 GRealThread *real = (GRealThread *) thread;
771
772 if (g_atomic_int_dec_and_test (&real->ref_count))
773 {
774 if (real->ours)
775 g_system_thread_free (real);
776 else
777 g_slice_free (GRealThread, real);
778 }
779 }
780
781 static void
g_thread_cleanup(gpointer data)782 g_thread_cleanup (gpointer data)
783 {
784 g_thread_unref (data);
785 }
786
787 gpointer
g_thread_proxy(gpointer data)788 g_thread_proxy (gpointer data)
789 {
790 GRealThread* thread = data;
791
792 g_assert (data);
793 g_private_set (&g_thread_specific_private, data);
794
795 TRACE (GLIB_THREAD_SPAWNED (thread->thread.func, thread->thread.data,
796 thread->name));
797
798 if (thread->name)
799 {
800 g_system_thread_set_name (thread->name);
801 g_free (thread->name);
802 thread->name = NULL;
803 }
804
805 thread->retval = thread->thread.func (thread->thread.data);
806
807 return NULL;
808 }
809
810 /**
811 * g_thread_new:
812 * @name: (nullable): an (optional) name for the new thread
813 * @func: a function to execute in the new thread
814 * @data: an argument to supply to the new thread
815 *
816 * This function creates a new thread. The new thread starts by invoking
817 * @func with the argument data. The thread will run until @func returns
818 * or until g_thread_exit() is called from the new thread. The return value
819 * of @func becomes the return value of the thread, which can be obtained
820 * with g_thread_join().
821 *
822 * The @name can be useful for discriminating threads in a debugger.
823 * It is not used for other purposes and does not have to be unique.
824 * Some systems restrict the length of @name to 16 bytes.
825 *
826 * If the thread can not be created the program aborts. See
827 * g_thread_try_new() if you want to attempt to deal with failures.
828 *
829 * If you are using threads to offload (potentially many) short-lived tasks,
830 * #GThreadPool may be more appropriate than manually spawning and tracking
831 * multiple #GThreads.
832 *
833 * To free the struct returned by this function, use g_thread_unref().
834 * Note that g_thread_join() implicitly unrefs the #GThread as well.
835 *
836 * Returns: the new #GThread
837 *
838 * Since: 2.32
839 */
840 GThread *
g_thread_new(const gchar * name,GThreadFunc func,gpointer data)841 g_thread_new (const gchar *name,
842 GThreadFunc func,
843 gpointer data)
844 {
845 GError *error = NULL;
846 GThread *thread;
847
848 thread = g_thread_new_internal (name, g_thread_proxy, func, data, 0, &error);
849
850 if G_UNLIKELY (thread == NULL)
851 g_error ("creating thread '%s': %s", name ? name : "", error->message);
852
853 return thread;
854 }
855
856 /**
857 * g_thread_try_new:
858 * @name: (nullable): an (optional) name for the new thread
859 * @func: a function to execute in the new thread
860 * @data: an argument to supply to the new thread
861 * @error: return location for error, or %NULL
862 *
863 * This function is the same as g_thread_new() except that
864 * it allows for the possibility of failure.
865 *
866 * If a thread can not be created (due to resource limits),
867 * @error is set and %NULL is returned.
868 *
869 * Returns: the new #GThread, or %NULL if an error occurred
870 *
871 * Since: 2.32
872 */
873 GThread *
g_thread_try_new(const gchar * name,GThreadFunc func,gpointer data,GError ** error)874 g_thread_try_new (const gchar *name,
875 GThreadFunc func,
876 gpointer data,
877 GError **error)
878 {
879 return g_thread_new_internal (name, g_thread_proxy, func, data, 0, error);
880 }
881
882 GThread *
g_thread_new_internal(const gchar * name,GThreadFunc proxy,GThreadFunc func,gpointer data,gsize stack_size,GError ** error)883 g_thread_new_internal (const gchar *name,
884 GThreadFunc proxy,
885 GThreadFunc func,
886 gpointer data,
887 gsize stack_size,
888 GError **error)
889 {
890 g_return_val_if_fail (func != NULL, NULL);
891
892 return (GThread*) g_system_thread_new (proxy, stack_size, name,
893 func, data, error);
894 }
895
896 /**
897 * g_thread_exit:
898 * @retval: the return value of this thread
899 *
900 * Terminates the current thread.
901 *
902 * If another thread is waiting for us using g_thread_join() then the
903 * waiting thread will be woken up and get @retval as the return value
904 * of g_thread_join().
905 *
906 * Calling g_thread_exit() with a parameter @retval is equivalent to
907 * returning @retval from the function @func, as given to g_thread_new().
908 *
909 * You must only call g_thread_exit() from a thread that you created
910 * yourself with g_thread_new() or related APIs. You must not call
911 * this function from a thread created with another threading library
912 * or or from within a #GThreadPool.
913 */
914 void
g_thread_exit(gpointer retval)915 g_thread_exit (gpointer retval)
916 {
917 GRealThread* real = (GRealThread*) g_thread_self ();
918
919 if G_UNLIKELY (!real->ours)
920 g_error ("attempt to g_thread_exit() a thread not created by GLib");
921
922 real->retval = retval;
923
924 g_system_thread_exit ();
925 }
926
927 /**
928 * g_thread_join:
929 * @thread: a #GThread
930 *
931 * Waits until @thread finishes, i.e. the function @func, as
932 * given to g_thread_new(), returns or g_thread_exit() is called.
933 * If @thread has already terminated, then g_thread_join()
934 * returns immediately.
935 *
936 * Any thread can wait for any other thread by calling g_thread_join(),
937 * not just its 'creator'. Calling g_thread_join() from multiple threads
938 * for the same @thread leads to undefined behaviour.
939 *
940 * The value returned by @func or given to g_thread_exit() is
941 * returned by this function.
942 *
943 * g_thread_join() consumes the reference to the passed-in @thread.
944 * This will usually cause the #GThread struct and associated resources
945 * to be freed. Use g_thread_ref() to obtain an extra reference if you
946 * want to keep the GThread alive beyond the g_thread_join() call.
947 *
948 * Returns: the return value of the thread
949 */
950 gpointer
g_thread_join(GThread * thread)951 g_thread_join (GThread *thread)
952 {
953 GRealThread *real = (GRealThread*) thread;
954 gpointer retval;
955
956 g_return_val_if_fail (thread, NULL);
957 g_return_val_if_fail (real->ours, NULL);
958
959 g_system_thread_wait (real);
960
961 retval = real->retval;
962
963 /* Just to make sure, this isn't used any more */
964 thread->joinable = 0;
965
966 g_thread_unref (thread);
967
968 return retval;
969 }
970
971 /**
972 * g_thread_self:
973 *
974 * This function returns the #GThread corresponding to the
975 * current thread. Note that this function does not increase
976 * the reference count of the returned struct.
977 *
978 * This function will return a #GThread even for threads that
979 * were not created by GLib (i.e. those created by other threading
980 * APIs). This may be useful for thread identification purposes
981 * (i.e. comparisons) but you must not use GLib functions (such
982 * as g_thread_join()) on these threads.
983 *
984 * Returns: the #GThread representing the current thread
985 */
986 GThread*
g_thread_self(void)987 g_thread_self (void)
988 {
989 GRealThread* thread = g_private_get (&g_thread_specific_private);
990
991 if (!thread)
992 {
993 /* If no thread data is available, provide and set one.
994 * This can happen for the main thread and for threads
995 * that are not created by GLib.
996 */
997 thread = g_slice_new0 (GRealThread);
998 thread->ref_count = 1;
999
1000 g_private_set (&g_thread_specific_private, thread);
1001 }
1002
1003 return (GThread*) thread;
1004 }
1005
1006 /**
1007 * g_get_num_processors:
1008 *
1009 * Determine the approximate number of threads that the system will
1010 * schedule simultaneously for this process. This is intended to be
1011 * used as a parameter to g_thread_pool_new() for CPU bound tasks and
1012 * similar cases.
1013 *
1014 * Returns: Number of schedulable threads, always greater than 0
1015 *
1016 * Since: 2.36
1017 */
1018 guint
g_get_num_processors(void)1019 g_get_num_processors (void)
1020 {
1021 #ifdef G_OS_WIN32
1022 unsigned int count;
1023 SYSTEM_INFO sysinfo;
1024 DWORD_PTR process_cpus;
1025 DWORD_PTR system_cpus;
1026
1027 /* This *never* fails, use it as fallback */
1028 GetNativeSystemInfo (&sysinfo);
1029 count = (int) sysinfo.dwNumberOfProcessors;
1030
1031 if (GetProcessAffinityMask (GetCurrentProcess (),
1032 &process_cpus, &system_cpus))
1033 {
1034 unsigned int af_count;
1035
1036 for (af_count = 0; process_cpus != 0; process_cpus >>= 1)
1037 if (process_cpus & 1)
1038 af_count++;
1039
1040 /* Prefer affinity-based result, if available */
1041 if (af_count > 0)
1042 count = af_count;
1043 }
1044
1045 if (count > 0)
1046 return count;
1047 #elif defined(_SC_NPROCESSORS_ONLN)
1048 {
1049 int count;
1050
1051 count = sysconf (_SC_NPROCESSORS_ONLN);
1052 if (count > 0)
1053 return count;
1054 }
1055 #elif defined HW_NCPU
1056 {
1057 int mib[2], count = 0;
1058 size_t len;
1059
1060 mib[0] = CTL_HW;
1061 mib[1] = HW_NCPU;
1062 len = sizeof(count);
1063
1064 if (sysctl (mib, 2, &count, &len, NULL, 0) == 0 && count > 0)
1065 return count;
1066 }
1067 #endif
1068
1069 return 1; /* Fallback */
1070 }
1071
1072 /* Epilogue {{{1 */
1073 /* vim: set foldmethod=marker: */
1074