334 lines
7.3 KiB
C
334 lines
7.3 KiB
C
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/*-
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* Copyright (c) 1998 Alex Nash
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $Id$
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*/
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#ifdef _THREAD_SAFE
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#include <errno.h>
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#include <limits.h>
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#include <stdlib.h>
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#include <pthread.h>
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#include "pthread_private.h"
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/* maximum number of times a read lock may be obtained */
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#define MAX_READ_LOCKS (INT_MAX - 1)
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static int init_static (pthread_rwlock_t *rwlock);
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static spinlock_t static_init_lock = _SPINLOCK_INITIALIZER;
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static int
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init_static (pthread_rwlock_t *rwlock)
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{
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int ret;
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_SPINLOCK(&static_init_lock);
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if (*rwlock == NULL)
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ret = pthread_rwlock_init(rwlock, NULL);
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else
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ret = 0;
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_SPINUNLOCK(&static_init_lock);
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return(ret);
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}
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int
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pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
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{
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int ret;
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if (rwlock == NULL)
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ret = EINVAL;
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else {
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pthread_rwlock_t prwlock;
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prwlock = *rwlock;
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pthread_mutex_destroy(&prwlock->lock);
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pthread_cond_destroy(&prwlock->read_signal);
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pthread_cond_destroy(&prwlock->write_signal);
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free(prwlock);
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*rwlock = NULL;
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}
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return(ret);
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}
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int
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pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
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{
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pthread_rwlock_t prwlock;
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int ret;
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/* allocate rwlock object */
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prwlock = (pthread_rwlock_t)malloc(sizeof(struct pthread_rwlock));
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if (prwlock == NULL)
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return(ENOMEM);
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/* initialize the lock */
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if ((ret = pthread_mutex_init(&prwlock->lock, NULL)) != 0)
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free(prwlock);
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else {
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/* initialize the read condition signal */
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ret = pthread_cond_init(&prwlock->read_signal, NULL);
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if (ret != 0) {
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pthread_mutex_destroy(&prwlock->lock);
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free(prwlock);
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} else {
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/* initialize the write condition signal */
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ret = pthread_cond_init(&prwlock->write_signal, NULL);
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if (ret != 0) {
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pthread_cond_destroy(&prwlock->read_signal);
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pthread_mutex_destroy(&prwlock->lock);
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free(prwlock);
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} else {
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/* success */
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prwlock->state = 0;
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prwlock->blocked_writers = 0;
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*rwlock = prwlock;
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}
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}
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}
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return(ret);
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}
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int
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pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
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{
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pthread_rwlock_t prwlock;
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int ret = 0;
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if (rwlock == NULL)
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return(EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if ((ret = init_static(rwlock)) != 0)
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return(ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
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return(ret);
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/* give writers priority over readers */
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while (prwlock->blocked_writers || prwlock->state < 0) {
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ret = pthread_cond_wait(&prwlock->read_signal, &prwlock->lock);
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if (ret != 0) {
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/* can't do a whole lot if this fails */
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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}
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/* check lock count */
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if (prwlock->state == MAX_READ_LOCKS)
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ret = EAGAIN;
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else
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++prwlock->state; /* indicate we are locked for reading */
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/*
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* Something is really wrong if this call fails. Returning
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* error won't do because we've already obtained the read
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* lock. Decrementing 'state' is no good because we probably
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* don't have the monitor lock.
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*/
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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int
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pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
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{
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pthread_rwlock_t prwlock;
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int ret = 0;
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if (rwlock == NULL)
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return(EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if ((ret = init_static(rwlock)) != 0)
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return(ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
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return(ret);
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/* give writers priority over readers */
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if (prwlock->blocked_writers || prwlock->state < 0)
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ret = EWOULDBLOCK;
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else if (prwlock->state == MAX_READ_LOCKS)
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ret = EAGAIN; /* too many read locks acquired */
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else
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++prwlock->state; /* indicate we are locked for reading */
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/* see the comment on this in pthread_rwlock_rdlock */
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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int
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pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
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{
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pthread_rwlock_t prwlock;
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int ret = 0;
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if (rwlock == NULL)
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return(EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if ((ret = init_static(rwlock)) != 0)
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return(ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
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return(ret);
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if (prwlock->state != 0)
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ret = EWOULDBLOCK;
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else
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/* indicate we are locked for writing */
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prwlock->state = -1;
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/* see the comment on this in pthread_rwlock_rdlock */
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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int
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pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
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{
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pthread_rwlock_t prwlock;
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int ret = 0;
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if (rwlock == NULL)
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return(EINVAL);
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prwlock = *rwlock;
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if (prwlock == NULL)
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return(EINVAL);
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/* grab the monitor lock */
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if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
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return(ret);
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if (prwlock->state > 0) {
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if (--prwlock->state == 0 && prwlock->blocked_writers)
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ret = pthread_cond_signal(&prwlock->write_signal);
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} else if (prwlock->state < 0) {
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prwlock->state = 0;
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if (prwlock->blocked_writers)
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ret = pthread_cond_signal(&prwlock->write_signal);
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else
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ret = pthread_cond_broadcast(&prwlock->read_signal);
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} else
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ret = EINVAL;
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/* see the comment on this in pthread_rwlock_rdlock */
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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int
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pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
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{
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pthread_rwlock_t prwlock;
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int ret = 0;
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if (rwlock == NULL)
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return(EINVAL);
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prwlock = *rwlock;
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/* check for static initialization */
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if (prwlock == NULL) {
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if ((ret = init_static(rwlock)) != 0)
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return(ret);
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prwlock = *rwlock;
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}
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/* grab the monitor lock */
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if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
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return(ret);
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while (prwlock->state != 0) {
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++prwlock->blocked_writers;
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ret = pthread_cond_wait(&prwlock->write_signal, &prwlock->lock);
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if (ret != 0) {
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--prwlock->blocked_writers;
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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--prwlock->blocked_writers;
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}
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/* indicate we are locked for writing */
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prwlock->state = -1;
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/* see the comment on this in pthread_rwlock_rdlock */
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pthread_mutex_unlock(&prwlock->lock);
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return(ret);
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}
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#endif /* _THREAD_SAFE */
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