1 /* GLIB - Library of useful routines for C programming
2 * Copyright (C) 1995-1997 Peter Mattis, Spencer Kimball and Josh MacDonald
4 * gthread.c: MT safety related functions
5 * Copyright 1998 Sebastian Wilhelmi; University of Karlsruhe
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.
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.
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/>.
22 /* Prelude {{{1 ----------------------------------------------------------- */
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/.
35 /* implement gthread.h's inline functions */
36 #define G_IMPLEMENT_INLINES 1
37 #define __G_THREAD_C__
42 #include "gthreadprivate.h"
55 #endif /* G_OS_WIN32 */
58 #include "gstrfuncs.h"
59 #include "gtestutils.h"
64 * @short_description: portable support for threads, mutexes, locks,
65 * conditions and thread private data
66 * @see_also: #GThreadPool, #GAsyncQueue
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.
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).
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.
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.
100 * Originally, UNIX did not have threads, and therefore some traditional
101 * UNIX APIs are problematic in threaded programs. Some notable examples
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()).
109 * - setenv() and unsetenv() manipulate the process environment in
110 * a not thread-safe way, and may interfere with getenv() calls
111 * 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.
117 * - setlocale() changes the locale for the entire process, affecting
118 * all threads. Temporary changes to the locale are often made to
119 * 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.
125 * - fork() only takes the calling thread into the child's copy of the
126 * 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.
132 * - daemon() uses fork() in a way contrary to what is described
133 * above. It should not be used with GLib programs.
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.
145 /* G_LOCK Documentation {{{1 ---------------------------------------------- */
149 * @name: the name of the lock
151 * The #G_LOCK_ macros provide a convenient interface to #GMutex.
152 * #G_LOCK_DEFINE defines a lock. It can appear in any place where
153 * variable definitions may appear in programs, i.e. in the first block
154 * of a function or outside of functions. The @name parameter will be
155 * mangled to get the name of the #GMutex. This means that you
156 * can use names of existing variables as the parameter - e.g. the name
157 * of the variable you intend to protect with the lock. Look at our
158 * give_me_next_number() example using the #G_LOCK macros:
160 * Here is an example for using the #G_LOCK convenience macros:
161 * |[<!-- language="C" -->
162 * G_LOCK_DEFINE (current_number);
165 * give_me_next_number (void)
167 * static int current_number = 0;
170 * G_LOCK (current_number);
171 * ret_val = current_number = calc_next_number (current_number);
172 * G_UNLOCK (current_number);
180 * G_LOCK_DEFINE_STATIC:
181 * @name: the name of the lock
183 * This works like #G_LOCK_DEFINE, but it creates a static object.
188 * @name: the name of the lock
190 * This declares a lock, that is defined with #G_LOCK_DEFINE in another
196 * @name: the name of the lock
198 * Works like g_mutex_lock(), but for a lock defined with
204 * @name: the name of the lock
206 * Works like g_mutex_trylock(), but for a lock defined with
209 * Returns: %TRUE, if the lock could be locked.
214 * @name: the name of the lock
216 * Works like g_mutex_unlock(), but for a lock defined with
220 /* GMutex Documentation {{{1 ------------------------------------------ */
225 * The #GMutex struct is an opaque data structure to represent a mutex
226 * (mutual exclusion). It can be used to protect data against shared
229 * Take for example the following function:
230 * |[<!-- language="C" -->
232 * give_me_next_number (void)
234 * static int current_number = 0;
236 * /* now do a very complicated calculation to calculate the new
237 * * number, this might for example be a random number generator
239 * current_number = calc_next_number (current_number);
241 * return current_number;
244 * It is easy to see that this won't work in a multi-threaded
245 * application. There current_number must be protected against shared
246 * access. A #GMutex can be used as a solution to this problem:
247 * |[<!-- language="C" -->
249 * give_me_next_number (void)
251 * static GMutex mutex;
252 * static int current_number = 0;
255 * g_mutex_lock (&mutex);
256 * ret_val = current_number = calc_next_number (current_number);
257 * g_mutex_unlock (&mutex);
262 * Notice that the #GMutex is not initialised to any particular value.
263 * Its placement in static storage ensures that it will be initialised
264 * to all-zeros, which is appropriate.
266 * If a #GMutex is placed in other contexts (eg: embedded in a struct)
267 * then it must be explicitly initialised using g_mutex_init().
269 * A #GMutex should only be accessed via g_mutex_ functions.
272 /* GRecMutex Documentation {{{1 -------------------------------------- */
277 * The GRecMutex struct is an opaque data structure to represent a
278 * recursive mutex. It is similar to a #GMutex with the difference
279 * that it is possible to lock a GRecMutex multiple times in the same
280 * thread without deadlock. When doing so, care has to be taken to
281 * unlock the recursive mutex as often as it has been locked.
283 * If a #GRecMutex is allocated in static storage then it can be used
284 * without initialisation. Otherwise, you should call
285 * g_rec_mutex_init() on it and g_rec_mutex_clear() when done.
287 * A GRecMutex should only be accessed with the
288 * g_rec_mutex_ functions.
293 /* GRWLock Documentation {{{1 ---------------------------------------- */
298 * The GRWLock struct is an opaque data structure to represent a
299 * reader-writer lock. It is similar to a #GMutex in that it allows
300 * multiple threads to coordinate access to a shared resource.
302 * The difference to a mutex is that a reader-writer lock discriminates
303 * between read-only ('reader') and full ('writer') access. While only
304 * one thread at a time is allowed write access (by holding the 'writer'
305 * lock via g_rw_lock_writer_lock()), multiple threads can gain
306 * simultaneous read-only access (by holding the 'reader' lock via
307 * g_rw_lock_reader_lock()).
309 * Here is an example for an array with access functions:
310 * |[<!-- language="C" -->
315 * my_array_get (guint index)
317 * gpointer retval = NULL;
322 * g_rw_lock_reader_lock (&lock);
323 * if (index < array->len)
324 * retval = g_ptr_array_index (array, index);
325 * g_rw_lock_reader_unlock (&lock);
331 * my_array_set (guint index, gpointer data)
333 * g_rw_lock_writer_lock (&lock);
336 * array = g_ptr_array_new ();
338 * if (index >= array->len)
339 * g_ptr_array_set_size (array, index+1);
340 * g_ptr_array_index (array, index) = data;
342 * g_rw_lock_writer_unlock (&lock);
345 * This example shows an array which can be accessed by many readers
346 * (the my_array_get() function) simultaneously, whereas the writers
347 * (the my_array_set() function) will only be allowed one at a time
348 * and only if no readers currently access the array. This is because
349 * of the potentially dangerous resizing of the array. Using these
350 * functions is fully multi-thread safe now.
352 * If a #GRWLock is allocated in static storage then it can be used
353 * without initialisation. Otherwise, you should call
354 * g_rw_lock_init() on it and g_rw_lock_clear() when done.
356 * A GRWLock should only be accessed with the g_rw_lock_ functions.
361 /* GCond Documentation {{{1 ------------------------------------------ */
366 * The #GCond struct is an opaque data structure that represents a
367 * condition. Threads can block on a #GCond if they find a certain
368 * condition to be false. If other threads change the state of this
369 * condition they signal the #GCond, and that causes the waiting
370 * threads to be woken up.
372 * Consider the following example of a shared variable. One or more
373 * threads can wait for data to be published to the variable and when
374 * another thread publishes the data, it can signal one of the waiting
375 * threads to wake up to collect the data.
377 * Here is an example for using GCond to block a thread until a condition
379 * |[<!-- language="C" -->
380 * gpointer current_data = NULL;
385 * push_data (gpointer data)
387 * g_mutex_lock (&data_mutex);
388 * current_data = data;
389 * g_cond_signal (&data_cond);
390 * g_mutex_unlock (&data_mutex);
398 * g_mutex_lock (&data_mutex);
399 * while (!current_data)
400 * g_cond_wait (&data_cond, &data_mutex);
401 * data = current_data;
402 * current_data = NULL;
403 * g_mutex_unlock (&data_mutex);
408 * Whenever a thread calls pop_data() now, it will wait until
409 * current_data is non-%NULL, i.e. until some other thread
410 * has called push_data().
412 * The example shows that use of a condition variable must always be
413 * paired with a mutex. Without the use of a mutex, there would be a
414 * race between the check of @current_data by the while loop in
415 * pop_data() and waiting. Specifically, another thread could set
416 * @current_data after the check, and signal the cond (with nobody
417 * waiting on it) before the first thread goes to sleep. #GCond is
418 * specifically useful for its ability to release the mutex and go
419 * to sleep atomically.
421 * It is also important to use the g_cond_wait() and g_cond_wait_until()
422 * functions only inside a loop which checks for the condition to be
423 * true. See g_cond_wait() for an explanation of why the condition may
424 * not be true even after it returns.
426 * If a #GCond is allocated in static storage then it can be used
427 * without initialisation. Otherwise, you should call g_cond_init()
428 * on it and g_cond_clear() when done.
430 * A #GCond should only be accessed via the g_cond_ functions.
433 /* GThread Documentation {{{1 ---------------------------------------- */
438 * The #GThread struct represents a running thread. This struct
439 * is returned by g_thread_new() or g_thread_try_new(). You can
440 * obtain the #GThread struct representing the current thread by
441 * calling g_thread_self().
443 * GThread is refcounted, see g_thread_ref() and g_thread_unref().
444 * The thread represented by it holds a reference while it is running,
445 * and g_thread_join() consumes the reference that it is given, so
446 * it is normally not necessary to manage GThread references
449 * The structure is opaque -- none of its fields may be directly
455 * @data: data passed to the thread
457 * Specifies the type of the @func functions passed to g_thread_new()
458 * or g_thread_try_new().
460 * Returns: the return value of the thread
464 * g_thread_supported:
466 * This macro returns %TRUE if the thread system is initialized,
467 * and %FALSE if it is not.
469 * For language bindings, g_thread_get_initialized() provides
470 * the same functionality as a function.
472 * Returns: %TRUE, if the thread system is initialized
475 /* GThreadError {{{1 ------------------------------------------------------- */
478 * @G_THREAD_ERROR_AGAIN: a thread couldn't be created due to resource
479 * shortage. Try again later.
481 * Possible errors of thread related functions.
487 * The error domain of the GLib thread subsystem.
489 G_DEFINE_QUARK (g_thread_error, g_thread_error)
491 /* Local Data {{{1 -------------------------------------------------------- */
493 static GMutex g_once_mutex;
494 static GCond g_once_cond;
495 static GSList *g_once_init_list = NULL;
497 static void g_thread_cleanup (gpointer data);
498 static GPrivate g_thread_specific_private = G_PRIVATE_INIT (g_thread_cleanup);
500 G_LOCK_DEFINE_STATIC (g_thread_new);
502 /* GOnce {{{1 ------------------------------------------------------------- */
506 * @status: the status of the #GOnce
507 * @retval: the value returned by the call to the function, if @status
508 * is %G_ONCE_STATUS_READY
510 * A #GOnce struct controls a one-time initialization function. Any
511 * one-time initialization function must have its own unique #GOnce
520 * A #GOnce must be initialized with this macro before it can be used.
522 * |[<!-- language="C" -->
523 * GOnce my_once = G_ONCE_INIT;
531 * @G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
532 * @G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
533 * @G_ONCE_STATUS_READY: the function has been called.
535 * The possible statuses of a one-time initialization function
536 * controlled by a #GOnce struct.
543 * @once: a #GOnce structure
544 * @func: the #GThreadFunc function associated to @once. This function
545 * is called only once, regardless of the number of times it and
546 * its associated #GOnce struct are passed to g_once().
547 * @arg: data to be passed to @func
549 * The first call to this routine by a process with a given #GOnce
550 * struct calls @func with the given argument. Thereafter, subsequent
551 * calls to g_once() with the same #GOnce struct do not call @func
552 * again, but return the stored result of the first call. On return
553 * from g_once(), the status of @once will be %G_ONCE_STATUS_READY.
555 * For example, a mutex or a thread-specific data key must be created
556 * exactly once. In a threaded environment, calling g_once() ensures
557 * that the initialization is serialized across multiple threads.
559 * Calling g_once() recursively on the same #GOnce struct in
560 * @func will lead to a deadlock.
562 * |[<!-- language="C" -->
564 * get_debug_flags (void)
566 * static GOnce my_once = G_ONCE_INIT;
568 * g_once (&my_once, parse_debug_flags, NULL);
570 * return my_once.retval;
577 g_once_impl (GOnce *once,
581 g_mutex_lock (&g_once_mutex);
583 while (once->status == G_ONCE_STATUS_PROGRESS)
584 g_cond_wait (&g_once_cond, &g_once_mutex);
586 if (once->status != G_ONCE_STATUS_READY)
588 once->status = G_ONCE_STATUS_PROGRESS;
589 g_mutex_unlock (&g_once_mutex);
591 once->retval = func (arg);
593 g_mutex_lock (&g_once_mutex);
594 once->status = G_ONCE_STATUS_READY;
595 g_cond_broadcast (&g_once_cond);
598 g_mutex_unlock (&g_once_mutex);
605 * @location: location of a static initializable variable containing 0
607 * Function to be called when starting a critical initialization
608 * section. The argument @location must point to a static
609 * 0-initialized variable that will be set to a value other than 0 at
610 * the end of the initialization section. In combination with
611 * g_once_init_leave() and the unique address @value_location, it can
612 * be ensured that an initialization section will be executed only once
613 * during a program's life time, and that concurrent threads are
614 * blocked until initialization completed. To be used in constructs
617 * |[<!-- language="C" -->
618 * static gsize initialization_value = 0;
620 * if (g_once_init_enter (&initialization_value))
622 * gsize setup_value = 42; /* initialization code here */
624 * g_once_init_leave (&initialization_value, setup_value);
627 * /* use initialization_value here */
630 * Returns: %TRUE if the initialization section should be entered,
631 * %FALSE and blocks otherwise
636 (g_once_init_enter) (volatile void *location)
638 volatile gsize *value_location = location;
639 gboolean need_init = FALSE;
640 g_mutex_lock (&g_once_mutex);
641 if (g_atomic_pointer_get (value_location) == NULL)
643 if (!g_slist_find (g_once_init_list, (void*) value_location))
646 g_once_init_list = g_slist_prepend (g_once_init_list, (void*) value_location);
650 g_cond_wait (&g_once_cond, &g_once_mutex);
651 while (g_slist_find (g_once_init_list, (void*) value_location));
653 g_mutex_unlock (&g_once_mutex);
659 * @location: location of a static initializable variable containing 0
660 * @result: new non-0 value for *@value_location
662 * Counterpart to g_once_init_enter(). Expects a location of a static
663 * 0-initialized initialization variable, and an initialization value
664 * other than 0. Sets the variable to the initialization value, and
665 * releases concurrent threads blocking in g_once_init_enter() on this
666 * initialization variable.
671 (g_once_init_leave) (volatile void *location,
674 volatile gsize *value_location = location;
676 g_return_if_fail (g_atomic_pointer_get (value_location) == NULL);
677 g_return_if_fail (result != 0);
678 g_return_if_fail (g_once_init_list != NULL);
680 g_atomic_pointer_set (value_location, result);
681 g_mutex_lock (&g_once_mutex);
682 g_once_init_list = g_slist_remove (g_once_init_list, (void*) value_location);
683 g_cond_broadcast (&g_once_cond);
684 g_mutex_unlock (&g_once_mutex);
687 /* GThread {{{1 -------------------------------------------------------- */
691 * @thread: a #GThread
693 * Increase the reference count on @thread.
695 * Returns: a new reference to @thread
700 g_thread_ref (GThread *thread)
702 GRealThread *real = (GRealThread *) thread;
704 g_atomic_int_inc (&real->ref_count);
711 * @thread: a #GThread
713 * Decrease the reference count on @thread, possibly freeing all
714 * resources associated with it.
716 * Note that each thread holds a reference to its #GThread while
717 * it is running, so it is safe to drop your own reference to it
718 * if you don't need it anymore.
723 g_thread_unref (GThread *thread)
725 GRealThread *real = (GRealThread *) thread;
727 if (g_atomic_int_dec_and_test (&real->ref_count))
730 g_system_thread_free (real);
732 g_slice_free (GRealThread, real);
737 g_thread_cleanup (gpointer data)
739 g_thread_unref (data);
743 g_thread_proxy (gpointer data)
745 GRealThread* thread = data;
749 /* This has to happen before G_LOCK, as that might call g_thread_self */
750 g_private_set (&g_thread_specific_private, data);
752 /* The lock makes sure that g_thread_new_internal() has a chance to
753 * setup 'func' and 'data' before we make the call.
755 G_LOCK (g_thread_new);
756 G_UNLOCK (g_thread_new);
760 g_system_thread_set_name (thread->name);
761 g_free (thread->name);
765 thread->retval = thread->thread.func (thread->thread.data);
772 * @name: (allow-none): an (optional) name for the new thread
773 * @func: a function to execute in the new thread
774 * @data: an argument to supply to the new thread
776 * This function creates a new thread. The new thread starts by invoking
777 * @func with the argument data. The thread will run until @func returns
778 * or until g_thread_exit() is called from the new thread. The return value
779 * of @func becomes the return value of the thread, which can be obtained
780 * with g_thread_join().
782 * The @name can be useful for discriminating threads in a debugger.
783 * It is not used for other purposes and does not have to be unique.
784 * Some systems restrict the length of @name to 16 bytes.
786 * If the thread can not be created the program aborts. See
787 * g_thread_try_new() if you want to attempt to deal with failures.
789 * To free the struct returned by this function, use g_thread_unref().
790 * Note that g_thread_join() implicitly unrefs the #GThread as well.
792 * Returns: the new #GThread
797 g_thread_new (const gchar *name,
801 GError *error = NULL;
804 thread = g_thread_new_internal (name, g_thread_proxy, func, data, 0, &error);
806 if G_UNLIKELY (thread == NULL)
807 g_error ("creating thread '%s': %s", name ? name : "", error->message);
814 * @name: (allow-none): an (optional) name for the new thread
815 * @func: a function to execute in the new thread
816 * @data: an argument to supply to the new thread
817 * @error: return location for error, or %NULL
819 * This function is the same as g_thread_new() except that
820 * it allows for the possibility of failure.
822 * If a thread can not be created (due to resource limits),
823 * @error is set and %NULL is returned.
825 * Returns: the new #GThread, or %NULL if an error occurred
830 g_thread_try_new (const gchar *name,
835 return g_thread_new_internal (name, g_thread_proxy, func, data, 0, error);
839 g_thread_new_internal (const gchar *name,
848 g_return_val_if_fail (func != NULL, NULL);
850 G_LOCK (g_thread_new);
851 thread = g_system_thread_new (proxy, stack_size, error);
854 thread->ref_count = 2;
856 thread->thread.joinable = TRUE;
857 thread->thread.func = func;
858 thread->thread.data = data;
859 thread->name = g_strdup (name);
861 G_UNLOCK (g_thread_new);
863 return (GThread*) thread;
868 * @retval: the return value of this thread
870 * Terminates the current thread.
872 * If another thread is waiting for us using g_thread_join() then the
873 * waiting thread will be woken up and get @retval as the return value
874 * of g_thread_join().
876 * Calling g_thread_exit() with a parameter @retval is equivalent to
877 * returning @retval from the function @func, as given to g_thread_new().
879 * You must only call g_thread_exit() from a thread that you created
880 * yourself with g_thread_new() or related APIs. You must not call
881 * this function from a thread created with another threading library
882 * or or from within a #GThreadPool.
885 g_thread_exit (gpointer retval)
887 GRealThread* real = (GRealThread*) g_thread_self ();
889 if G_UNLIKELY (!real->ours)
890 g_error ("attempt to g_thread_exit() a thread not created by GLib");
892 real->retval = retval;
894 g_system_thread_exit ();
899 * @thread: a #GThread
901 * Waits until @thread finishes, i.e. the function @func, as
902 * given to g_thread_new(), returns or g_thread_exit() is called.
903 * If @thread has already terminated, then g_thread_join()
904 * returns immediately.
906 * Any thread can wait for any other thread by calling g_thread_join(),
907 * not just its 'creator'. Calling g_thread_join() from multiple threads
908 * for the same @thread leads to undefined behaviour.
910 * The value returned by @func or given to g_thread_exit() is
911 * returned by this function.
913 * g_thread_join() consumes the reference to the passed-in @thread.
914 * This will usually cause the #GThread struct and associated resources
915 * to be freed. Use g_thread_ref() to obtain an extra reference if you
916 * want to keep the GThread alive beyond the g_thread_join() call.
918 * Returns: the return value of the thread
921 g_thread_join (GThread *thread)
923 GRealThread *real = (GRealThread*) thread;
926 g_return_val_if_fail (thread, NULL);
927 g_return_val_if_fail (real->ours, NULL);
929 g_system_thread_wait (real);
931 retval = real->retval;
933 /* Just to make sure, this isn't used any more */
934 thread->joinable = 0;
936 g_thread_unref (thread);
944 * This functions returns the #GThread corresponding to the
945 * current thread. Note that this function does not increase
946 * the reference count of the returned struct.
948 * This function will return a #GThread even for threads that
949 * were not created by GLib (i.e. those created by other threading
950 * APIs). This may be useful for thread identification purposes
951 * (i.e. comparisons) but you must not use GLib functions (such
952 * as g_thread_join()) on these threads.
954 * Returns: the #GThread representing the current thread
959 GRealThread* thread = g_private_get (&g_thread_specific_private);
963 /* If no thread data is available, provide and set one.
964 * This can happen for the main thread and for threads
965 * that are not created by GLib.
967 thread = g_slice_new0 (GRealThread);
968 thread->ref_count = 1;
970 g_private_set (&g_thread_specific_private, thread);
973 return (GThread*) thread;
977 * g_get_num_processors:
979 * Determine the approximate number of threads that the system will
980 * schedule simultaneously for this process. This is intended to be
981 * used as a parameter to g_thread_pool_new() for CPU bound tasks and
984 * Returns: Number of schedulable threads, always greater than 0
989 g_get_num_processors (void)
992 DWORD_PTR process_cpus;
993 DWORD_PTR system_cpus;
995 if (GetProcessAffinityMask (GetCurrentProcess (),
996 &process_cpus, &system_cpus))
1000 for (count = 0; process_cpus != 0; process_cpus >>= 1)
1001 if (process_cpus & 1)
1007 #elif defined(_SC_NPROCESSORS_ONLN)
1011 count = sysconf (_SC_NPROCESSORS_ONLN);
1015 #elif defined HW_NCPU
1017 int mib[2], count = 0;
1022 len = sizeof(count);
1024 if (sysctl (mib, 2, &count, &len, NULL, 0) == 0 && count > 0)
1029 return 1; /* Fallback */
1033 /* vim: set foldmethod=marker: */