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, write to the
20 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
21 * Boston, MA 02111-1307, USA.
24 /* Prelude {{{1 ----------------------------------------------------------- */
27 * Modified by the GLib Team and others 1997-2000. See the AUTHORS
28 * file for a list of people on the GLib Team. See the ChangeLog
29 * files for a list of changes. These files are distributed with
30 * GLib at ftp://ftp.gtk.org/pub/gtk/.
37 /* implement gthread.h's inline functions */
38 #define G_IMPLEMENT_INLINES 1
39 #define __G_THREAD_C__
44 #include "gthreadprivate.h"
57 #endif /* G_OS_WIN32 */
60 #include "gtestutils.h"
65 * @short_description: portable support for threads, mutexes, locks,
66 * conditions and thread private data
67 * @see_also: #GThreadPool, #GAsyncQueue
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.
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 thread
86 * has a private instance of (#GPrivate). There are
87 * facilities for one-time initialization (#GOnce, g_once_init_enter()).
88 * Finally there are primitives to create and manage threads (#GThread).
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. It is still possible to do thread-unsafe
95 * initialization and setup at the beginning of your program, before
96 * creating the first threads.
98 * GLib is internally completely thread-safe (all global data is
99 * automatically locked), but individual data structure instances are
100 * not automatically locked for performance reasons. For example,
101 * you must coordinate accesses to the same #GHashTable from multiple
102 * threads. The two notable exceptions from this rule are #GMainLoop
103 * and #GAsyncQueue, which <emphasis>are</emphasis> thread-safe and
104 * need no further application-level locking to be accessed from
105 * multiple threads. Most refcounting functions such as g_object_ref()
106 * are also thread-safe.
109 /* G_LOCK Documentation {{{1 ---------------------------------------------- */
113 * @name: the name of the lock
115 * The %G_LOCK_* macros provide a convenient interface to #GMutex.
116 * #G_LOCK_DEFINE defines a lock. It can appear in any place where
117 * variable definitions may appear in programs, i.e. in the first block
118 * of a function or outside of functions. The @name parameter will be
119 * mangled to get the name of the #GMutex. This means that you
120 * can use names of existing variables as the parameter - e.g. the name
121 * of the variable you intend to protect with the lock. Look at our
122 * <function>give_me_next_number()</function> example using the
126 * <title>Using the %G_LOCK_* convenience macros</title>
128 * G_LOCK_DEFINE (current_number);
131 * give_me_next_number (void)
133 * static int current_number = 0;
136 * G_LOCK (current_number);
137 * ret_val = current_number = calc_next_number (current_number);
138 * G_UNLOCK (current_number);
147 * G_LOCK_DEFINE_STATIC:
148 * @name: the name of the lock
150 * This works like #G_LOCK_DEFINE, but it creates a static object.
155 * @name: the name of the lock
157 * This declares a lock, that is defined with #G_LOCK_DEFINE in another
163 * @name: the name of the lock
165 * Works like g_mutex_lock(), but for a lock defined with
171 * @name: the name of the lock
172 * @Returns: %TRUE, if the lock could be locked.
174 * Works like g_mutex_trylock(), but for a lock defined with
180 * @name: the name of the lock
182 * Works like g_mutex_unlock(), but for a lock defined with
186 /* GMutex Documentation {{{1 ------------------------------------------ */
191 * The #GMutex struct is an opaque data structure to represent a mutex
192 * (mutual exclusion). It can be used to protect data against shared
193 * access. Take for example the following function:
196 * <title>A function which will not work in a threaded environment</title>
199 * give_me_next_number (void)
201 * static int current_number = 0;
203 * /<!-- -->* now do a very complicated calculation to calculate the new
204 * * number, this might for example be a random number generator
206 * current_number = calc_next_number (current_number);
208 * return current_number;
213 * It is easy to see that this won't work in a multi-threaded
214 * application. There current_number must be protected against shared
215 * access. A #GMutex can be used as a solution to this problem:
218 * <title>Using GMutex to protected a shared variable</title>
221 * give_me_next_number (void)
223 * static GMutex mutex;
224 * static int current_number = 0;
227 * g_mutex_lock (&mutex);
228 * ret_val = current_number = calc_next_number (current_number);
229 * g_mutex_unlock (&mutex);
236 * Notice that the #GMutex is not initialised to any particular value.
237 * Its placement in static storage ensures that it will be initialised
238 * to all-zeros, which is appropriate.
240 * If a #GMutex is placed in other contexts (eg: embedded in a struct)
241 * then it must be explicitly initialised using g_mutex_init().
243 * A #GMutex should only be accessed via <function>g_mutex_</function>
247 /* GRecMutex Documentation {{{1 -------------------------------------- */
252 * The GRecMutex struct is an opaque data structure to represent a
253 * recursive mutex. It is similar to a #GMutex with the difference
254 * that it is possible to lock a GRecMutex multiple times in the same
255 * thread without deadlock. When doing so, care has to be taken to
256 * unlock the recursive mutex as often as it has been locked.
258 * If a #GRecMutex is allocated in static storage then it can be used
259 * without initialisation. Otherwise, you should call
260 * g_rec_mutex_init() on it and g_rec_mutex_clear() when done.
262 * A GRecMutex should only be accessed with the
263 * <function>g_rec_mutex_</function> functions.
268 /* GRWLock Documentation {{{1 ---------------------------------------- */
273 * The GRWLock struct is an opaque data structure to represent a
274 * reader-writer lock. It is similar to a #GMutex in that it allows
275 * multiple threads to coordinate access to a shared resource.
277 * The difference to a mutex is that a reader-writer lock discriminates
278 * between read-only ('reader') and full ('writer') access. While only
279 * one thread at a time is allowed write access (by holding the 'writer'
280 * lock via g_rw_lock_writer_lock()), multiple threads can gain
281 * simultaneous read-only access (by holding the 'reader' lock via
282 * g_rw_lock_reader_lock()).
285 * <title>An array with access functions</title>
291 * my_array_get (guint index)
293 * gpointer retval = NULL;
298 * g_rw_lock_reader_lock (&lock);
299 * if (index < array->len)
300 * retval = g_ptr_array_index (array, index);
301 * g_rw_lock_reader_unlock (&lock);
307 * my_array_set (guint index, gpointer data)
309 * g_rw_lock_writer_lock (&lock);
312 * array = g_ptr_array_new (<!-- -->);
314 * if (index >= array->len)
315 * g_ptr_array_set_size (array, index+1);
316 * g_ptr_array_index (array, index) = data;
318 * g_rw_lock_writer_unlock (&lock);
322 * This example shows an array which can be accessed by many readers
323 * (the <function>my_array_get()</function> function) simultaneously,
324 * whereas the writers (the <function>my_array_set()</function>
325 * function) will only be allowed once at a time and only if no readers
326 * currently access the array. This is because of the potentially
327 * dangerous resizing of the array. Using these functions is fully
328 * multi-thread safe now.
332 * If a #GRWLock is allocated in static storage then it can be used
333 * without initialisation. Otherwise, you should call
334 * g_rw_lock_init() on it and g_rw_lock_clear() when done.
336 * A GRWLock should only be accessed with the
337 * <function>g_rw_lock_</function> functions.
342 /* GCond Documentation {{{1 ------------------------------------------ */
347 * The #GCond struct is an opaque data structure that represents a
348 * condition. Threads can block on a #GCond if they find a certain
349 * condition to be false. If other threads change the state of this
350 * condition they signal the #GCond, and that causes the waiting
351 * threads to be woken up.
355 * Using GCond to block a thread until a condition is satisfied
358 * GCond* data_cond = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
359 * GMutex* data_mutex = NULL; /<!-- -->* Must be initialized somewhere *<!-- -->/
360 * gpointer current_data = NULL;
363 * push_data (gpointer data)
365 * g_mutex_lock (data_mutex);
366 * current_data = data;
367 * g_cond_signal (data_cond);
368 * g_mutex_unlock (data_mutex);
376 * g_mutex_lock (data_mutex);
377 * while (!current_data)
378 * g_cond_wait (data_cond, data_mutex);
379 * data = current_data;
380 * current_data = NULL;
381 * g_mutex_unlock (data_mutex);
388 * Whenever a thread calls pop_data() now, it will wait until
389 * current_data is non-%NULL, i.e. until some other thread
390 * has called push_data().
392 * <note><para>It is important to use the g_cond_wait() and
393 * g_cond_timed_wait() functions only inside a loop which checks for the
394 * condition to be true. It is not guaranteed that the waiting thread
395 * will find the condition fulfilled after it wakes up, even if the
396 * signaling thread left the condition in that state: another thread may
397 * have altered the condition before the waiting thread got the chance
398 * to be woken up, even if the condition itself is protected by a
399 * #GMutex, like above.</para></note>
401 * If a #GCond is allocated in static storage then it can be used
402 * without initialisation. Otherwise, you should call g_cond_init() on
403 * it and g_cond_clear() when done.
405 * A #GCond should only be accessed via the <function>g_cond_</function>
409 /* GThread Documentation {{{1 ---------------------------------------- */
414 * The #GThread struct represents a running thread. This struct
415 * is returned by g_thread_new() or g_thread_try(). You can obtain the
416 * #GThread struct representing the current thead by calling
419 * The structure is opaque -- none of its fields may be directly
425 * @data: data passed to the thread
427 * Specifies the type of the @func functions passed to g_thread_new() or
430 * Returns: the return value of the thread
434 * g_thread_supported:
436 * This macro returns %TRUE if the thread system is initialized,
437 * and %FALSE if it is not.
439 * For language bindings, g_thread_get_initialized() provides
440 * the same functionality as a function.
442 * Returns: %TRUE, if the thread system is initialized
445 /* GThreadError {{{1 ------------------------------------------------------- */
448 * @G_THREAD_ERROR_AGAIN: a thread couldn't be created due to resource
449 * shortage. Try again later.
451 * Possible errors of thread related functions.
457 * The error domain of the GLib thread subsystem.
460 g_thread_error_quark (void)
462 return g_quark_from_static_string ("g_thread_error");
465 /* Local Data {{{1 -------------------------------------------------------- */
467 static GMutex g_once_mutex;
468 static GCond g_once_cond;
469 static GSList *g_once_init_list = NULL;
471 static void g_thread_cleanup (gpointer data);
472 static GPrivate g_thread_specific_private = G_PRIVATE_INIT (g_thread_cleanup);
474 G_LOCK_DEFINE_STATIC (g_thread_new);
476 /* GOnce {{{1 ------------------------------------------------------------- */
480 * @status: the status of the #GOnce
481 * @retval: the value returned by the call to the function, if @status
482 * is %G_ONCE_STATUS_READY
484 * A #GOnce struct controls a one-time initialization function. Any
485 * one-time initialization function must have its own unique #GOnce
494 * A #GOnce must be initialized with this macro before it can be used.
497 * GOnce my_once = G_ONCE_INIT;
505 * @G_ONCE_STATUS_NOTCALLED: the function has not been called yet.
506 * @G_ONCE_STATUS_PROGRESS: the function call is currently in progress.
507 * @G_ONCE_STATUS_READY: the function has been called.
509 * The possible statuses of a one-time initialization function
510 * controlled by a #GOnce struct.
517 * @once: a #GOnce structure
518 * @func: the #GThreadFunc function associated to @once. This function
519 * is called only once, regardless of the number of times it and
520 * its associated #GOnce struct are passed to g_once().
521 * @arg: data to be passed to @func
523 * The first call to this routine by a process with a given #GOnce
524 * struct calls @func with the given argument. Thereafter, subsequent
525 * calls to g_once() with the same #GOnce struct do not call @func
526 * again, but return the stored result of the first call. On return
527 * from g_once(), the status of @once will be %G_ONCE_STATUS_READY.
529 * For example, a mutex or a thread-specific data key must be created
530 * exactly once. In a threaded environment, calling g_once() ensures
531 * that the initialization is serialized across multiple threads.
533 * Calling g_once() recursively on the same #GOnce struct in
534 * @func will lead to a deadlock.
538 * get_debug_flags (void)
540 * static GOnce my_once = G_ONCE_INIT;
542 * g_once (&my_once, parse_debug_flags, NULL);
544 * return my_once.retval;
551 g_once_impl (GOnce *once,
555 g_mutex_lock (&g_once_mutex);
557 while (once->status == G_ONCE_STATUS_PROGRESS)
558 g_cond_wait (&g_once_cond, &g_once_mutex);
560 if (once->status != G_ONCE_STATUS_READY)
562 once->status = G_ONCE_STATUS_PROGRESS;
563 g_mutex_unlock (&g_once_mutex);
565 once->retval = func (arg);
567 g_mutex_lock (&g_once_mutex);
568 once->status = G_ONCE_STATUS_READY;
569 g_cond_broadcast (&g_once_cond);
572 g_mutex_unlock (&g_once_mutex);
579 * @value_location: location of a static initializable variable
582 * Function to be called when starting a critical initialization
583 * section. The argument @value_location must point to a static
584 * 0-initialized variable that will be set to a value other than 0 at
585 * the end of the initialization section. In combination with
586 * g_once_init_leave() and the unique address @value_location, it can
587 * be ensured that an initialization section will be executed only once
588 * during a program's life time, and that concurrent threads are
589 * blocked until initialization completed. To be used in constructs
593 * static gsize initialization_value = 0;
595 * if (g_once_init_enter (&initialization_value))
597 * gsize setup_value = 42; /** initialization code here **/
599 * g_once_init_leave (&initialization_value, setup_value);
602 * /** use initialization_value here **/
605 * Returns: %TRUE if the initialization section should be entered,
606 * %FALSE and blocks otherwise
611 (g_once_init_enter) (volatile void *pointer)
613 volatile gsize *value_location = pointer;
614 gboolean need_init = FALSE;
615 g_mutex_lock (&g_once_mutex);
616 if (g_atomic_pointer_get (value_location) == NULL)
618 if (!g_slist_find (g_once_init_list, (void*) value_location))
621 g_once_init_list = g_slist_prepend (g_once_init_list, (void*) value_location);
625 g_cond_wait (&g_once_cond, &g_once_mutex);
626 while (g_slist_find (g_once_init_list, (void*) value_location));
628 g_mutex_unlock (&g_once_mutex);
634 * @value_location: location of a static initializable variable
636 * @result: new non-0 value for *@value_location
638 * Counterpart to g_once_init_enter(). Expects a location of a static
639 * 0-initialized initialization variable, and an initialization value
640 * other than 0. Sets the variable to the initialization value, and
641 * releases concurrent threads blocking in g_once_init_enter() on this
642 * initialization variable.
647 (g_once_init_leave) (volatile void *pointer,
650 volatile gsize *value_location = pointer;
652 g_return_if_fail (g_atomic_pointer_get (value_location) == NULL);
653 g_return_if_fail (result != 0);
654 g_return_if_fail (g_once_init_list != NULL);
656 g_atomic_pointer_set (value_location, result);
657 g_mutex_lock (&g_once_mutex);
658 g_once_init_list = g_slist_remove (g_once_init_list, (void*) value_location);
659 g_cond_broadcast (&g_once_cond);
660 g_mutex_unlock (&g_once_mutex);
663 /* GThread {{{1 -------------------------------------------------------- */
666 g_thread_ref (GThread *thread)
668 GRealThread *real = (GRealThread *) thread;
670 g_atomic_int_inc (&real->ref_count);
676 g_thread_unref (GThread *thread)
678 GRealThread *real = (GRealThread *) thread;
680 if (g_atomic_int_dec_and_test (&real->ref_count))
683 g_system_thread_free (real);
685 g_slice_free (GRealThread, real);
690 g_thread_cleanup (gpointer data)
692 g_thread_unref (data);
696 g_thread_proxy (gpointer data)
698 GRealThread* thread = data;
703 g_system_thread_set_name (thread->name);
705 /* This has to happen before G_LOCK, as that might call g_thread_self */
706 g_private_set (&g_thread_specific_private, data);
708 /* The lock makes sure that g_thread_new_internal() has a chance to
709 * setup 'func' and 'data' before we make the call.
711 G_LOCK (g_thread_new);
712 G_UNLOCK (g_thread_new);
714 thread->retval = thread->thread.func (thread->thread.data);
721 * @name: a name for the new thread
722 * @func: a function to execute in the new thread
723 * @data: an argument to supply to the new thread
724 * @error: return location for error
726 * This function creates a new thread. The new thread starts by invoking
727 * @func with the argument data. The thread will run until @func returns
728 * or until g_thread_exit() is called from the new thread.
730 * The @name can be useful for discriminating threads in
731 * a debugger. Some systems restrict the length of @name to
734 * If the thread can not be created the program aborts. See
735 * g_thread_try() if you want to attempt to deal with failures.
737 * Returns: the new #GThread
742 g_thread_new (const gchar *name,
746 GError *error = NULL;
749 thread = g_thread_new_internal (name, g_thread_proxy, func, data, 0, &error);
751 if G_UNLIKELY (thread == NULL)
752 g_error ("creating thread '%s': %s", name ? name : "", error->message);
759 * @name: a name for the new thread
760 * @func: a function to execute in the new thread
761 * @data: an argument to supply to the new thread
762 * @error: return location for error
764 * This function is the same as g_thread_new() except that it allows for
765 * the possibility of failure.
767 * If a thread can not be created (due to resource limits), @error is
768 * set and %NULL is returned.
770 * Returns: the new #GThread, or %NULL if an error occurred
775 g_thread_try (const gchar *name,
780 return g_thread_new_internal (name, g_thread_proxy, func, data, 0, error);
784 g_thread_new_internal (const gchar *name,
793 g_return_val_if_fail (func != NULL, NULL);
795 G_LOCK (g_thread_new);
796 thread = g_system_thread_new (proxy, stack_size, error);
799 thread->ref_count = 2;
801 thread->thread.joinable = TRUE;
802 thread->thread.func = func;
803 thread->thread.data = data;
806 G_UNLOCK (g_thread_new);
808 return (GThread*) thread;
813 * @retval: the return value of this thread
815 * Terminates the current thread.
817 * If another thread is waiting for us using g_thread_join() then the
818 * waiting thread will be woken up and get @retval as the return value
819 * of g_thread_join().
821 * Calling <literal>g_thread_exit (retval)</literal> is equivalent to
822 * returning @retval from the function @func, as given to g_thread_new().
824 * <note><para>Never call g_thread_exit() from within a thread of a
825 * #GThreadPool, as that will mess up the bookkeeping and lead to funny
826 * and unwanted results.</para></note>
829 g_thread_exit (gpointer retval)
831 GRealThread* real = (GRealThread*) g_thread_self ();
832 real->retval = retval;
834 g_system_thread_exit ();
839 * @thread: a #GThread
841 * Waits until @thread finishes, i.e. the function @func, as
842 * given to g_thread_new(), returns or g_thread_exit() is called.
843 * If @thread has already terminated, then g_thread_join()
844 * returns immediately.
846 * Any thread can wait for any other thread by calling g_thread_join(),
847 * not just its 'creator'. Calling g_thread_join() from multiple threads
848 * for the same @thread leads to undefined behaviour.
850 * The value returned by @func or given to g_thread_exit() is
851 * returned by this function.
853 * All resources of @thread including the #GThread struct are
854 * released before g_thread_join() returns.
856 * Returns: the return value of the thread
859 g_thread_join (GThread *thread)
861 GRealThread *real = (GRealThread*) thread;
864 g_return_val_if_fail (thread, NULL);
866 g_system_thread_wait (real);
868 retval = real->retval;
870 /* Just to make sure, this isn't used any more */
871 thread->joinable = 0;
873 g_thread_unref (thread);
881 * This functions returns the #GThread corresponding to the
884 * Returns: the #GThread representing the current thread
889 GRealThread* thread = g_private_get (&g_thread_specific_private);
893 /* If no thread data is available, provide and set one.
894 * This can happen for the main thread and for threads
895 * that are not created by GLib.
897 thread = g_slice_new0 (GRealThread);
898 thread->ref_count = 1;
900 g_private_set (&g_thread_specific_private, thread);
903 return (GThread*) thread;
907 /* vim: set foldmethod=marker: */