/* Linuxthreads - a simple clone()-based implementation of Posix */ /* threads for Linux. */ /* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr) */ /* and Pavel Krauz (krauz@fsid.cvut.cz). */ /* */ /* 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. */ /* Condition variables */ #include <errno.h> #include <sched.h> #include <stddef.h> #include <sys/time.h> #include "pthread.h" #include "internals.h" #include "spinlock.h" #include "queue.h" #include "restart.h" int pthread_cond_init(pthread_cond_t *cond, const pthread_condattr_t *cond_attr attribute_unused) { __pthread_init_lock(&cond->__c_lock); cond->__c_waiting = NULL; return 0; } int pthread_cond_destroy(pthread_cond_t *cond) { if (cond->__c_waiting != NULL) return EBUSY; return 0; } /* Function called by pthread_cancel to remove the thread from waiting on a condition variable queue. */ static int cond_extricate_func(void *obj, pthread_descr th) { volatile pthread_descr self = thread_self(); pthread_cond_t *cond = obj; int did_remove = 0; __pthread_lock(&cond->__c_lock, self); did_remove = remove_from_queue(&cond->__c_waiting, th); __pthread_unlock(&cond->__c_lock); return did_remove; } int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex) { volatile pthread_descr self = thread_self(); pthread_extricate_if extr; int already_canceled = 0; int spurious_wakeup_count; /* Check whether the mutex is locked and owned by this thread. */ if (mutex->__m_kind != PTHREAD_MUTEX_TIMED_NP && mutex->__m_kind != PTHREAD_MUTEX_ADAPTIVE_NP && mutex->__m_owner != self) return EINVAL; /* Set up extrication interface */ extr.pu_object = cond; extr.pu_extricate_func = cond_extricate_func; /* Register extrication interface */ THREAD_SETMEM(self, p_condvar_avail, 0); __pthread_set_own_extricate_if(self, &extr); /* Atomically enqueue thread for waiting, but only if it is not canceled. If the thread is canceled, then it will fall through the suspend call below, and then call pthread_exit without having to worry about whether it is still on the condition variable queue. This depends on pthread_cancel setting p_canceled before calling the extricate function. */ __pthread_lock(&cond->__c_lock, self); if (!(THREAD_GETMEM(self, p_canceled) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) enqueue(&cond->__c_waiting, self); else already_canceled = 1; __pthread_unlock(&cond->__c_lock); if (already_canceled) { __pthread_set_own_extricate_if(self, 0); pthread_exit(PTHREAD_CANCELED); } pthread_mutex_unlock(mutex); spurious_wakeup_count = 0; while (1) { suspend(self); if (THREAD_GETMEM(self, p_condvar_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); /* Check for cancellation again, to provide correct cancellation point behavior */ 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_mutex_lock(mutex); pthread_exit(PTHREAD_CANCELED); } /* Put back any resumes we caught that don't belong to us. */ while (spurious_wakeup_count--) restart(self); pthread_mutex_lock(mutex); return 0; } static int pthread_cond_timedwait_relative(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec * abstime) { volatile pthread_descr self = thread_self(); int already_canceled = 0; pthread_extricate_if extr; int spurious_wakeup_count; /* Check whether the mutex is locked and owned by this thread. */ if (mutex->__m_kind != PTHREAD_MUTEX_TIMED_NP && mutex->__m_kind != PTHREAD_MUTEX_ADAPTIVE_NP && mutex->__m_owner != self) return EINVAL; /* Set up extrication interface */ extr.pu_object = cond; extr.pu_extricate_func = cond_extricate_func; /* Register extrication interface */ THREAD_SETMEM(self, p_condvar_avail, 0); __pthread_set_own_extricate_if(self, &extr); /* Enqueue to wait on the condition and check for cancellation. */ __pthread_lock(&cond->__c_lock, self); if (!(THREAD_GETMEM(self, p_canceled) && THREAD_GETMEM(self, p_cancelstate) == PTHREAD_CANCEL_ENABLE)) enqueue(&cond->__c_waiting, self); else already_canceled = 1; __pthread_unlock(&cond->__c_lock); if (already_canceled) { __pthread_set_own_extricate_if(self, 0); pthread_exit(PTHREAD_CANCELED); } pthread_mutex_unlock(mutex); spurious_wakeup_count = 0; while (1) { if (!timedsuspend(self, abstime)) { int was_on_queue; /* __pthread_lock will queue back any spurious restarts that may happen to it. */ __pthread_lock(&cond->__c_lock, self); was_on_queue = remove_from_queue(&cond->__c_waiting, self); __pthread_unlock(&cond->__c_lock); if (was_on_queue) { __pthread_set_own_extricate_if(self, 0); pthread_mutex_lock(mutex); return ETIMEDOUT; } /* Eat the outstanding restart() from the signaller */ suspend(self); } if (THREAD_GETMEM(self, p_condvar_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); /* The remaining logic is the same as in other cancellable waits, such as pthread_join sem_wait or pthread_cond wait. */ 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_mutex_lock(mutex); pthread_exit(PTHREAD_CANCELED); } /* Put back any resumes we caught that don't belong to us. */ while (spurious_wakeup_count--) restart(self); pthread_mutex_lock(mutex); return 0; } int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec * abstime) { /* Indirect call through pointer! */ return pthread_cond_timedwait_relative(cond, mutex, abstime); } int pthread_cond_signal(pthread_cond_t *cond) { pthread_descr th; __pthread_lock(&cond->__c_lock, NULL); th = dequeue(&cond->__c_waiting); __pthread_unlock(&cond->__c_lock); if (th != NULL) { th->p_condvar_avail = 1; WRITE_MEMORY_BARRIER(); restart(th); } return 0; } int pthread_cond_broadcast(pthread_cond_t *cond) { pthread_descr tosignal, th; __pthread_lock(&cond->__c_lock, NULL); /* Copy the current state of the waiting queue and empty it */ tosignal = cond->__c_waiting; cond->__c_waiting = NULL; __pthread_unlock(&cond->__c_lock); /* Now signal each process in the queue */ while ((th = dequeue(&tosignal)) != NULL) { th->p_condvar_avail = 1; WRITE_MEMORY_BARRIER(); restart(th); } return 0; } int pthread_condattr_init(pthread_condattr_t *attr attribute_unused) { return 0; } int pthread_condattr_destroy(pthread_condattr_t *attr attribute_unused) { return 0; } int pthread_condattr_getpshared (const pthread_condattr_t *attr attribute_unused, int *pshared) { *pshared = PTHREAD_PROCESS_PRIVATE; return 0; } int pthread_condattr_setpshared (pthread_condattr_t *attr attribute_unused, int pshared) { if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED) return EINVAL; /* For now it is not possible to shared a conditional variable. */ if (pshared != PTHREAD_PROCESS_PRIVATE) return ENOSYS; return 0; }