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