/* Linuxthreads - a simple clone()-based implementation of Posix */ /* threads for Linux. */ /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */ /* */ /* This program is free software; you can redistribute it and/or */ /* modify it under the terms of the GNU Library General Public License */ /* as published by the Free Software Foundation; either version 2 */ /* of the License, or (at your option) any later version. */ /* */ /* This program is distributed in the hope that it will be useful, */ /* but WITHOUT ANY WARRANTY; without even the implied warranty of */ /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */ /* GNU Library General Public License for more details. */ /* Semaphores a la POSIX 1003.1b */ #include <features.h> #include <limits.h> #include <errno.h> #include "pthread.h" #include "semaphore.h" #include "internals.h" #include "spinlock.h" #include "restart.h" #include "queue.h" int sem_init(sem_t *sem, int pshared, unsigned int value) { if (value > SEM_VALUE_MAX) { errno = EINVAL; return -1; } if (pshared) { errno = ENOSYS; return -1; } __pthread_init_lock(&sem->__sem_lock); sem->__sem_value = value; sem->__sem_waiting = NULL; return 0; } /* Function called by pthread_cancel to remove the thread from waiting inside sem_wait. */ static int new_sem_extricate_func(void *obj, pthread_descr th) { volatile pthread_descr self = thread_self(); sem_t *sem = obj; int did_remove = 0; __pthread_lock(&sem->__sem_lock, self); did_remove = remove_from_queue(&sem->__sem_waiting, th); __pthread_unlock(&sem->__sem_lock); return did_remove; } int sem_wait(sem_t * sem) { volatile pthread_descr self = thread_self(); pthread_extricate_if extr; int already_canceled = 0; int spurious_wakeup_count; /* Set up extrication interface */ extr.pu_object = sem; extr.pu_extricate_func = new_sem_extricate_func; __pthread_lock(&sem->__sem_lock, self); if (sem->__sem_value > 0) { sem->__sem_value--; __pthread_unlock(&sem->__sem_lock); return 0; } /* Register extrication interface */ THREAD_SETMEM(self, p_sem_avail, 0); __pthread_set_own_extricate_if(self, &extr); /* Enqueue only if not already cancelled. */ if (!(THREAD_GETMEM(self, p_canceled) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) enqueue(&sem->__sem_waiting, self); else already_canceled = 1; __pthread_unlock(&sem->__sem_lock); if (already_canceled) { __pthread_set_own_extricate_if(self, 0); __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME); } /* Wait for sem_post or cancellation, or fall through if already canceled */ spurious_wakeup_count = 0; while (1) { suspend(self); if (THREAD_GETMEM(self, p_sem_avail) == 0 && (THREAD_GETMEM(self, p_woken_by_cancel) == 0 || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE)) { /* Count resumes that don't belong to us. */ spurious_wakeup_count++; continue; } break; } __pthread_set_own_extricate_if(self, 0); /* Terminate only if the wakeup came from cancellation. */ /* Otherwise ignore cancellation because we got the semaphore. */ if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { THREAD_SETMEM(self, p_woken_by_cancel, 0); __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME); } /* We got the semaphore */ return 0; } int sem_trywait(sem_t * sem) { int retval; __pthread_lock(&sem->__sem_lock, NULL); if (sem->__sem_value == 0) { errno = EAGAIN; retval = -1; } else { sem->__sem_value--; retval = 0; } __pthread_unlock(&sem->__sem_lock); return retval; } int sem_post(sem_t * sem) { pthread_descr self = thread_self(); pthread_descr th; struct pthread_request request; if (THREAD_GETMEM(self, p_in_sighandler) == NULL) { __pthread_lock(&sem->__sem_lock, self); if (sem->__sem_waiting == NULL) { if (sem->__sem_value >= SEM_VALUE_MAX) { /* Overflow */ errno = ERANGE; __pthread_unlock(&sem->__sem_lock); return -1; } sem->__sem_value++; __pthread_unlock(&sem->__sem_lock); } else { th = dequeue(&sem->__sem_waiting); __pthread_unlock(&sem->__sem_lock); th->p_sem_avail = 1; WRITE_MEMORY_BARRIER(); restart(th); } } else { /* If we're in signal handler, delegate post operation to the thread manager. */ if (__pthread_manager_request < 0) { if (__pthread_initialize_manager() < 0) { errno = EAGAIN; return -1; } } request.req_kind = REQ_POST; request.req_args.post = sem; TEMP_FAILURE_RETRY(write(__pthread_manager_request, (char *) &request, sizeof(request))); } return 0; } int sem_getvalue(sem_t * sem, int * sval) { *sval = sem->__sem_value; return 0; } int sem_destroy(sem_t * sem) { if (sem->__sem_waiting != NULL) { __set_errno (EBUSY); return -1; } return 0; } sem_t *sem_open(const char *name attribute_unused, int oflag attribute_unused, ...) { __set_errno (ENOSYS); return SEM_FAILED; } int sem_close(sem_t *sem attribute_unused) { __set_errno (ENOSYS); return -1; } int sem_unlink(const char *name attribute_unused) { __set_errno (ENOSYS); return -1; } int sem_timedwait(sem_t *sem, const struct timespec *abstime) { pthread_descr self = thread_self(); pthread_extricate_if extr; int already_canceled = 0; int spurious_wakeup_count; __pthread_lock(&sem->__sem_lock, self); if (sem->__sem_value > 0) { --sem->__sem_value; __pthread_unlock(&sem->__sem_lock); return 0; } if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000) { /* The standard requires that if the function would block and the time value is illegal, the function returns with an error. */ __pthread_unlock(&sem->__sem_lock); __set_errno (EINVAL); return -1; } /* Set up extrication interface */ extr.pu_object = sem; extr.pu_extricate_func = new_sem_extricate_func; /* Register extrication interface */ THREAD_SETMEM(self, p_sem_avail, 0); __pthread_set_own_extricate_if(self, &extr); /* Enqueue only if not already cancelled. */ if (!(THREAD_GETMEM(self, p_canceled) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) enqueue(&sem->__sem_waiting, self); else already_canceled = 1; __pthread_unlock(&sem->__sem_lock); if (already_canceled) { __pthread_set_own_extricate_if(self, 0); __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME); } spurious_wakeup_count = 0; while (1) { if (timedsuspend(self, abstime) == 0) { int was_on_queue; /* __pthread_lock will queue back any spurious restarts that may happen to it. */ __pthread_lock(&sem->__sem_lock, self); was_on_queue = remove_from_queue(&sem->__sem_waiting, self); __pthread_unlock(&sem->__sem_lock); if (was_on_queue) { __pthread_set_own_extricate_if(self, 0); __set_errno (ETIMEDOUT); return -1; } /* Eat the outstanding restart() from the signaller */ suspend(self); } if (THREAD_GETMEM(self, p_sem_avail) == 0 && (THREAD_GETMEM(self, p_woken_by_cancel) == 0 || THREAD_GETMEM(self, p_cancelstate) != PTHREAD_CANCEL_ENABLE)) { /* Count resumes that don't belong to us. */ spurious_wakeup_count++; continue; } break; } __pthread_set_own_extricate_if(self, 0); /* Terminate only if the wakeup came from cancellation. */ /* Otherwise ignore cancellation because we got the semaphore. */ if (THREAD_GETMEM(self, p_woken_by_cancel) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE) { THREAD_SETMEM(self, p_woken_by_cancel, 0); __pthread_do_exit(PTHREAD_CANCELED, CURRENT_STACK_FRAME); } /* We got the semaphore */ return 0; }