rt-thread/components/pthreads/pthread_rwlock.c

#include <pthread.h>

int pthread_rwlockattr_init (pthread_rwlockattr_t * attr)
{
	if (!attr) return EINVAL;
	*attr = PTHREAD_PROCESS_PRIVATE;

	return 0;
}

int pthread_rwlockattr_destroy (pthread_rwlockattr_t * attr)
{
	if (!attr) return EINVAL;

	return 0;
}

int pthread_rwlockattr_getpshared (const pthread_rwlockattr_t * attr, int *pshared)
{
	if (!attr || !pshared) return EINVAL;

	*pshared = PTHREAD_PROCESS_PRIVATE;
	return 0;
}

int pthread_rwlockattr_setpshared (pthread_rwlockattr_t * attr, int pshared)
{
	if (!attr || pshared != PTHREAD_PROCESS_PRIVATE) return EINVAL;

	return 0;
}

int pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t * attr)
{
	if (!rwlock) return EINVAL;

	rwlock->attr = PTHREAD_PROCESS_PRIVATE;
	pthread_mutex_init(&(rwlock->rw_mutex), NULL);
	pthread_cond_init(&(rwlock->rw_condreaders), NULL);
	pthread_cond_init(&(rwlock->rw_condwriters), NULL);
	
	rwlock->rw_nwaitwriters = 0;
	rwlock->rw_nwaitreaders = 0;
	rwlock->rw_refcount = 0;

	return 0;
}

int pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) return 0; /* rwlock is not initialized */

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if (rwlock->rw_refcount != 0 ||
		rwlock->rw_nwaitreaders != 0 || rwlock->rw_nwaitwriters != 0)
	{
		result = EBUSY;
		return(EBUSY);
	}
	else
	{
		/* check whether busy */
		result = rt_sem_trytake(&(rwlock->rw_condreaders.sem));
		if (result == RT_EOK)
		{
			result = rt_sem_trytake(&(rwlock->rw_condwriters.sem));
			if (result == RT_EOK)
			{
				rt_sem_release(&(rwlock->rw_condreaders.sem));
				rt_sem_release(&(rwlock->rw_condwriters.sem));

				pthread_cond_destroy(&rwlock->rw_condreaders);
				pthread_cond_destroy(&rwlock->rw_condwriters);
			}
			else
			{
				rt_sem_release(&(rwlock->rw_condreaders.sem));
				result = EBUSY;
			}
		}
		else result = EBUSY;
	}

	pthread_mutex_unlock(&rwlock->rw_mutex);
	if (result == 0) pthread_mutex_destroy(&rwlock->rw_mutex);
	
	return result;
}

int pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	/* give preference to waiting writers */
	while (rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
	{
		rwlock->rw_nwaitreaders++;
		result = pthread_cond_wait(&rwlock->rw_condreaders, &rwlock->rw_mutex);
		rwlock->rw_nwaitreaders--;
		if (result != 0)
			break;
	}

	/* another reader has a read lock */
	if (result == 0) rwlock->rw_refcount++;

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return (result);
}

int pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ((result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if (rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
		result = EBUSY;                 /* held by a writer or waiting writers */
	else
		rwlock->rw_refcount++;          /* increment count of reader locks */

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return(result);
}

int pthread_rwlock_timedrdlock (pthread_rwlock_t * rwlock, const struct timespec *abstime)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	/* give preference to waiting writers */
	while (rwlock->rw_refcount < 0 || rwlock->rw_nwaitwriters > 0)
	{
		rwlock->rw_nwaitreaders++;
		result = pthread_cond_timedwait(&rwlock->rw_condreaders, &rwlock->rw_mutex, abstime);
		rwlock->rw_nwaitreaders--;
		if (result != 0)
			break;
	}

	/* another reader has a read lock */
	if (result == 0) rwlock->rw_refcount++;

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return (result);
}

int pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	while (rwlock->rw_refcount != 0)
	{
		rwlock->rw_nwaitwriters++;
		result = pthread_cond_timedwait(&rwlock->rw_condwriters, &rwlock->rw_mutex, abstime);
		rwlock->rw_nwaitwriters--;
		
		if (result != 0) break;
	}

	if (result == 0) rwlock->rw_refcount = -1;

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return(result);
}

int pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if (rwlock->rw_refcount != 0)
		result = EBUSY;                 /* held by either writer or reader(s) */
	else
		rwlock->rw_refcount = -1;   	/* available, indicate a writer has it */

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return(result);
}

int pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	if (rwlock->rw_refcount > 0)
		rwlock->rw_refcount--;              /* releasing a reader */
	else if (rwlock->rw_refcount == -1)
		rwlock->rw_refcount = 0;            /* releasing a reader */

	/* give preference to waiting writers over waiting readers */
	if (rwlock->rw_nwaitwriters > 0)
	{
		if (rwlock->rw_refcount == 0)
			result = pthread_cond_signal(&rwlock->rw_condwriters);
	}
	else if (rwlock->rw_nwaitreaders > 0)
	{
		result = pthread_cond_broadcast(&rwlock->rw_condreaders);
	}

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return(result);
}

int pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
	int result;

	if (!rwlock) return EINVAL;
	if (rwlock->attr == -1) pthread_rwlock_init(rwlock, NULL);

	if ( (result = pthread_mutex_lock(&rwlock->rw_mutex)) != 0)
		return(result);

	while (rwlock->rw_refcount != 0)
	{
		rwlock->rw_nwaitwriters++;
		result = pthread_cond_wait(&rwlock->rw_condwriters, &rwlock->rw_mutex);
		rwlock->rw_nwaitwriters--;
		
		if (result != 0) break;
	}

	if (result == 0) rwlock->rw_refcount = -1;

	pthread_mutex_unlock(&rwlock->rw_mutex);
	return(result);
}