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//
// rwlock.c
//
// POSIX read-write locks
//
// Copyright (C) 2002 Michael Ringgaard. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
//
// 1. Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
// 3. Neither the name of the project nor the names of its contributors
// may be used to endorse or promote products derived from this software
// without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
#include <os.h>
#include <pthread.h>
int pthread_rwlockattr_init(pthread_rwlockattr_t *attr) {
if (!attr) return EINVAL;
attr->pshared = PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_rwlockattr_destroy(pthread_rwlockattr_t *attr) {
return 0;
}
int pthread_rwlockattr_getpshared(const pthread_rwlockattr_t *attr, int *pshared) {
if (!attr || !pshared) return EINVAL;
*pshared = attr->pshared;
return 0;
}
int pthread_rwlockattr_setpshared(pthread_rwlockattr_t *attr, int pshared) {
if (!attr) return EINVAL;
if (pshared != PTHREAD_PROCESS_PRIVATE && pshared != PTHREAD_PROCESS_SHARED) return EINVAL;
attr->pshared = pshared;
return 0;
}
int pthread_rwlock_init(pthread_rwlock_t *lock, const pthread_rwlockattr_t *attr) {
int rc;
if (!lock) return EINVAL;
if (attr && attr->pshared == PTHREAD_PROCESS_SHARED) return ENOSYS;
lock->num_active = 0;
lock->exclusive_waiters = 0;
lock->num_shared_waiters = 0;
lock->owner = NOHANDLE;
rc = pthread_mutex_init(&lock->mutex, NULL);
if (rc != 0) return rc;
lock->exclusive_waiters = mksem(0);
if (lock->exclusive_waiters < 0) return errno;
lock->shared_waiters = mksem(0);
if (lock->shared_waiters < 0) return errno;
return 0;
}
int pthread_rwlock_destroy(pthread_rwlock_t *lock) {
if (!lock) return EINVAL;
pthread_mutex_destroy(&lock->mutex);
if (close(lock->exclusive_waiters) < 0) return errno;
if (close(lock->shared_waiters) < 0) return errno;
return 0;
}
int pthread_rwlock_tryrdlock(pthread_rwlock_t *lock) {
int rc = 0;
pthread_mutex_lock(&lock->mutex);
if (lock->num_active < 0) {
if (pthread_equal(lock->owner, pthread_self())) {
lock->num_active--;
} else {
rc = EBUSY;
}
} else {
lock->num_active++;
}
pthread_mutex_unlock(&lock->mutex);
return rc;
}
int pthread_rwlock_trywrlock(pthread_rwlock_t *lock) {
int rc = 0;
pthread_mutex_lock(&lock->mutex);
if (lock->num_active == 0) {
// Lock is free
lock->num_active = -1;
lock->owner = pthread_self();
} else if (lock->num_active < 0) {
// Exclusive lock in progress
if (pthread_equal(lock->owner, pthread_self())) {
lock->num_active--;
} else {
rc = EBUSY;
}
}
pthread_mutex_unlock(&lock->mutex);
return 0;
}
int pthread_rwlock_rdlock(pthread_rwlock_t *lock) {
return pthread_rwlock_timedrdlock(lock, NULL);
}
int pthread_rwlock_timedrdlock(pthread_rwlock_t *lock, const struct timespec *abstime) {
pthread_mutex_lock(&lock->mutex);
while (1) {
if (lock->num_active < 0) {
if (pthread_equal(lock->owner, pthread_self())) {
lock->num_active--;
break;
}
lock->num_shared_waiters++;
pthread_mutex_unlock(&lock->mutex);
if (waitone(lock->shared_waiters, __abstime2timeout(abstime)) < 0) return errno;
pthread_mutex_lock(&lock->mutex);
} else {
lock->num_active++;
break;
}
}
pthread_mutex_unlock(&lock->mutex);
return 0;
}
int pthread_rwlock_wrlock(pthread_rwlock_t *lock) {
return pthread_rwlock_timedwrlock(lock, NULL);
}
int pthread_rwlock_timedwrlock(pthread_rwlock_t *lock, const struct timespec *abstime) {
pthread_mutex_lock(&lock->mutex);
while (1) {
if (lock->num_active == 0) {
// Lock is free
lock->num_active = -1;
lock->owner = pthread_self();
break;
} else if (lock->num_active < 0) {
// Exclusive lock in progress
if (pthread_equal(lock->owner, pthread_self())) {
lock->num_active--;
break;
}
}
// Wait for lock to be released
lock->exclusive_waiters++;
pthread_mutex_unlock(&lock->mutex);
if (waitone(lock->exclusive_waiters, __abstime2timeout(abstime)) < 0) return errno;
pthread_mutex_lock(&lock->mutex);
}
pthread_mutex_unlock(&lock->mutex);
return 0;
}
int pthread_rwlock_unlock(pthread_rwlock_t *lock) {
pthread_mutex_lock(&lock->mutex);
if (lock->num_active > 0) {
// Have one or more readers
if (--lock->num_active == 0) {
if (lock->num_exclusive_waiters > 0) {
lock->num_exclusive_waiters--;
semrel(lock->exclusive_waiters, 1);
}
}
} else if (lock->num_active < 0) {
// Have a writer, possibly recursive
if (++lock->num_active == 0) {
lock->owner = NOHANDLE;
if (lock->num_exclusive_waiters > 0) {
lock->num_exclusive_waiters--;
semrel(lock->exclusive_waiters, 1);
} else if (lock->num_shared_waiters > 0) {
int num = lock->num_shared_waiters;
lock->num_active = num;
lock->num_shared_waiters = 0;
semrel(lock->shared_waiters, num);
}
}
}
pthread_mutex_unlock(&lock->mutex);
return 0;
}