1 /* Linuxthreads - a simple clone()-based implementation of Posix */
2 /* threads for Linux. */
3 /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */
5 /* This program is free software; you can redistribute it and/or */
6 /* modify it under the terms of the GNU Library General Public License */
7 /* as published by the Free Software Foundation; either version 2 */
8 /* of the License, or (at your option) any later version. */
10 /* This program is distributed in the hope that it will be useful, */
11 /* but WITHOUT ANY WARRANTY; without even the implied warranty of */
12 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
13 /* GNU Library General Public License for more details. */
15 /* Semaphores a la POSIX 1003.1b */
21 #include "semaphore.h"
22 #include "internals.h"
27 int sem_init(sem_t *sem, int pshared, unsigned int value)
29 if (value > SEM_VALUE_MAX) {
37 __pthread_init_lock(&sem->__sem_lock);
38 sem->__sem_value = value;
39 sem->__sem_waiting = NULL;
43 /* Function called by pthread_cancel to remove the thread from
44 waiting inside sem_wait. */
46 static int new_sem_extricate_func(void *obj, pthread_descr th)
48 volatile pthread_descr self = thread_self();
52 __pthread_lock(&sem->__sem_lock, self);
53 did_remove = remove_from_queue(&sem->__sem_waiting, th);
54 __pthread_unlock(&sem->__sem_lock);
59 int sem_wait(sem_t * sem)
61 volatile pthread_descr self = thread_self();
62 pthread_extricate_if extr;
63 int already_canceled = 0;
64 int spurious_wakeup_count;
66 /* Set up extrication interface */
68 extr.pu_extricate_func = new_sem_extricate_func;
70 __pthread_lock(&sem->__sem_lock, self);
71 if (sem->__sem_value > 0) {
73 __pthread_unlock(&sem->__sem_lock);
76 /* Register extrication interface */
77 THREAD_SETMEM(self, p_sem_avail, 0);
78 __pthread_set_own_extricate_if(self, &extr);
79 /* Enqueue only if not already cancelled. */
80 if (!(THREAD_GETMEM(self, p_canceled)
81 && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
82 enqueue(&sem->__sem_waiting, self);
85 __pthread_unlock(&sem->__sem_lock);
87 if (already_canceled) {
88 __pthread_set_own_extricate_if(self, 0);
89 __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
92 /* Wait for sem_post or cancellation, or fall through if already canceled */
93 spurious_wakeup_count = 0;
97 if (THREAD_GETMEM(self, p_sem_avail) == 0
98 && (THREAD_GETMEM(self, p_woken_by_cancel) == 0
99 || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE))
101 /* Count resumes that don't belong to us. */
102 spurious_wakeup_count++;
107 __pthread_set_own_extricate_if(self, 0);
109 /* Terminate only if the wakeup came from cancellation. */
110 /* Otherwise ignore cancellation because we got the semaphore. */
112 if (THREAD_GETMEM(self, p_woken_by_cancel)
113 && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
114 THREAD_SETMEM(self, p_woken_by_cancel, 0);
115 __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
117 /* We got the semaphore */
121 int sem_trywait(sem_t * sem)
125 __pthread_lock(&sem->__sem_lock, NULL);
126 if (sem->__sem_value == 0) {
133 __pthread_unlock(&sem->__sem_lock);
137 int sem_post(sem_t * sem)
139 pthread_descr self = thread_self();
141 struct pthread_request request;
143 if (THREAD_GETMEM(self, p_in_sighandler) == NULL) {
144 __pthread_lock(&sem->__sem_lock, self);
145 if (sem->__sem_waiting == NULL) {
146 if (sem->__sem_value >= SEM_VALUE_MAX) {
149 __pthread_unlock(&sem->__sem_lock);
153 __pthread_unlock(&sem->__sem_lock);
155 th = dequeue(&sem->__sem_waiting);
156 __pthread_unlock(&sem->__sem_lock);
158 WRITE_MEMORY_BARRIER();
162 /* If we're in signal handler, delegate post operation to
163 the thread manager. */
164 if (__pthread_manager_request < 0) {
165 if (__pthread_initialize_manager() < 0) {
170 request.req_kind = REQ_POST;
171 request.req_args.post = sem;
172 TEMP_FAILURE_RETRY(write(__pthread_manager_request,
173 (char *) &request, sizeof(request)));
178 int sem_getvalue(sem_t * sem, int * sval)
180 *sval = sem->__sem_value;
184 int sem_destroy(sem_t * sem)
186 if (sem->__sem_waiting != NULL) {
193 sem_t *sem_open(const char *name attribute_unused, int oflag attribute_unused, ...)
195 __set_errno (ENOSYS);
199 int sem_close(sem_t *sem attribute_unused)
201 __set_errno (ENOSYS);
205 int sem_unlink(const char *name attribute_unused)
207 __set_errno (ENOSYS);
211 int sem_timedwait(sem_t *sem, const struct timespec *abstime)
213 pthread_descr self = thread_self();
214 pthread_extricate_if extr;
215 int already_canceled = 0;
216 int spurious_wakeup_count;
218 __pthread_lock(&sem->__sem_lock, self);
219 if (sem->__sem_value > 0) {
221 __pthread_unlock(&sem->__sem_lock);
225 if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000) {
226 /* The standard requires that if the function would block and the
227 time value is illegal, the function returns with an error. */
228 __pthread_unlock(&sem->__sem_lock);
229 __set_errno (EINVAL);
233 /* Set up extrication interface */
234 extr.pu_object = sem;
235 extr.pu_extricate_func = new_sem_extricate_func;
237 /* Register extrication interface */
238 THREAD_SETMEM(self, p_sem_avail, 0);
239 __pthread_set_own_extricate_if(self, &extr);
240 /* Enqueue only if not already cancelled. */
241 if (!(THREAD_GETMEM(self, p_canceled)
242 && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE))
243 enqueue(&sem->__sem_waiting, self);
245 already_canceled = 1;
246 __pthread_unlock(&sem->__sem_lock);
248 if (already_canceled) {
249 __pthread_set_own_extricate_if(self, 0);
250 __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
253 spurious_wakeup_count = 0;
256 if (timedsuspend(self, abstime) == 0) {
259 /* __pthread_lock will queue back any spurious restarts that
262 __pthread_lock(&sem->__sem_lock, self);
263 was_on_queue = remove_from_queue(&sem->__sem_waiting, self);
264 __pthread_unlock(&sem->__sem_lock);
267 __pthread_set_own_extricate_if(self, 0);
268 __set_errno (ETIMEDOUT);
272 /* Eat the outstanding restart() from the signaller */
276 if (THREAD_GETMEM(self, p_sem_avail) == 0
277 && (THREAD_GETMEM(self, p_woken_by_cancel) == 0
278 || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE))
280 /* Count resumes that don't belong to us. */
281 spurious_wakeup_count++;
287 __pthread_set_own_extricate_if(self, 0);
289 /* Terminate only if the wakeup came from cancellation. */
290 /* Otherwise ignore cancellation because we got the semaphore. */
292 if (THREAD_GETMEM(self, p_woken_by_cancel)
293 && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) {
294 THREAD_SETMEM(self, p_woken_by_cancel, 0);
295 __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME);
297 /* We got the semaphore */