/* * pthread_cond_destroy.c * * Description: * This translation unit implements condition variables and their primitives. * * * -------------------------------------------------------------------------- * * Pthreads-embedded (PTE) - POSIX Threads Library for embedded systems * Copyright(C) 2008 Jason Schmidlapp * * Contact Email: jschmidlapp@users.sourceforge.net * * * Based upon Pthreads-win32 - POSIX Threads Library for Win32 * Copyright(C) 1998 John E. Bossom * Copyright(C) 1999,2005 Pthreads-win32 contributors * * Contact Email: rpj@callisto.canberra.edu.au * * The original list of contributors to the Pthreads-win32 project * is contained in the file CONTRIBUTORS.ptw32 included with the * source code distribution. The list can also be seen at the * following World Wide Web location: * http://sources.redhat.com/pthreads-win32/contributors.html * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2 of the License, or (at your option) any later version. * * This library 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 * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library in the file COPYING.LIB; * if not, write to the Free Software Foundation, Inc., * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA */ #include #include "pthread.h" #include "implement.h" int pthread_cond_destroy (pthread_cond_t * cond) /* * ------------------------------------------------------ * DOCPUBLIC * This function destroys a condition variable * * * PARAMETERS * cond * pointer to an instance of pthread_cond_t * * * DESCRIPTION * This function destroys a condition variable. * * NOTES: * 1) A condition variable can be destroyed * immediately after all the threads that * are blocked on it are awakened. e.g. * * struct list { * pthread_mutex_t lm; * ... * } * * struct elt { * key k; * int busy; * pthread_cond_t notbusy; * ... * } * * * struct elt * * list_find(struct list *lp, key k) * { * struct elt *ep; * * pthread_mutex_lock(&lp->lm); * while ((ep = find_elt(l,k) != NULL) && ep->busy) * pthread_cond_wait(&ep->notbusy, &lp->lm); * if (ep != NULL) * ep->busy = 1; * pthread_mutex_unlock(&lp->lm); * return(ep); * } * * delete_elt(struct list *lp, struct elt *ep) * { * pthread_mutex_lock(&lp->lm); * assert(ep->busy); * ... remove ep from list ... * ep->busy = 0; * (A) pthread_cond_broadcast(&ep->notbusy); * pthread_mutex_unlock(&lp->lm); * (B) pthread_cond_destroy(&rp->notbusy); * free(ep); * } * * In this example, the condition variable * and its list element may be freed (line B) * immediately after all threads waiting for * it are awakened (line A), since the mutex * and the code ensure that no other thread * can touch the element to be deleted. * * RESULTS * 0 successfully released condition variable, * EINVAL 'cond' is invalid, * EBUSY 'cond' is in use, * * ------------------------------------------------------ */ { pthread_cond_t cv; int result = 0, result1 = 0, result2 = 0; /* * Assuming any race condition here is harmless. */ if (cond == NULL || *cond == NULL) { return EINVAL; } if (*cond != PTHREAD_COND_INITIALIZER) { pte_osMutexLock (pte_cond_list_lock); cv = *cond; /* * Close the gate; this will synchronize this thread with * all already signaled waiters to let them retract their * waiter status - SEE NOTE 1 ABOVE!!! */ if (sem_wait (&(cv->semBlockLock)) != 0) { return errno; } /* * !TRY! lock mtxUnblockLock; try will detect busy condition * and will not cause a deadlock with respect to concurrent * signal/broadcast. */ if ((result = pthread_mutex_trylock (&(cv->mtxUnblockLock))) != 0) { (void) sem_post (&(cv->semBlockLock)); return result; } /* * Check whether cv is still busy (still has waiters) */ if (cv->nWaitersBlocked > cv->nWaitersGone) { if (sem_post (&(cv->semBlockLock)) != 0) { result = errno; } result1 = pthread_mutex_unlock (&(cv->mtxUnblockLock)); result2 = EBUSY; } else { /* * Now it is safe to destroy */ *cond = NULL; if (sem_destroy (&(cv->semBlockLock)) != 0) { result = errno; } if (sem_destroy (&(cv->semBlockQueue)) != 0) { result1 = errno; } if ((result2 = pthread_mutex_unlock (&(cv->mtxUnblockLock))) == 0) { result2 = pthread_mutex_destroy (&(cv->mtxUnblockLock)); } /* Unlink the CV from the list */ if (pte_cond_list_head == cv) { pte_cond_list_head = cv->next; } else { cv->prev->next = cv->next; } if (pte_cond_list_tail == cv) { pte_cond_list_tail = cv->prev; } else { cv->next->prev = cv->prev; } (void) free (cv); } pte_osMutexUnlock(pte_cond_list_lock); } else { /* * See notes in pte_cond_check_need_init() above also. */ pte_osMutexLock (pte_cond_test_init_lock); /* * Check again. */ if (*cond == PTHREAD_COND_INITIALIZER) { /* * This is all we need to do to destroy a statically * initialised cond that has not yet been used (initialised). * If we get to here, another thread waiting to initialise * this cond will get an EINVAL. That's OK. */ *cond = NULL; } else { /* * The cv has been initialised while we were waiting * so assume it's in use. */ result = EBUSY; } pte_osMutexUnlock(pte_cond_test_init_lock); } return ((result != 0) ? result : ((result1 != 0) ? result1 : result2)); }