xref: /dflybsd-src/lib/libthread_xu/thread/thr_rwlock.c (revision cf8046a92768d53e67d2533fb51b137d5506248d)

/*-
 * Copyright (c) 1998 Alex Nash
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
 *
 * $FreeBSD: src/lib/libpthread/thread/thr_rwlock.c,v 1.14 2004/01/08 15:37:09 deischen Exp $
 */

#include "namespace.h"
#include <machine/tls.h>
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <pthread.h>
#include "un-namespace.h"
#include "thr_private.h"

#ifdef _PTHREADS_DEBUGGING

#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <sys/file.h>

#endif

/* maximum number of times a read lock may be obtained */
#define	MAX_READ_LOCKS		(INT_MAX - 1)

umtx_t	_rwlock_static_lock;

#ifdef _PTHREADS_DEBUGGING

static
void
rwlock_log(const char *ctl, ...)
{
	char buf[256];
	va_list va;
	size_t len;

	va_start(va, ctl);
	len = vsnprintf(buf, sizeof(buf), ctl, va);
	va_end(va);
	_thr_log(buf, len);
}

#else

static __inline
void
rwlock_log(const char *ctl __unused, ...)
{
}

#endif

static int
rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
{
	pthread_rwlock_t prwlock;
	int ret;

	/* allocate rwlock object */
	prwlock = __malloc(sizeof(struct __pthread_rwlock_s));
	if (prwlock == NULL)
		return (ENOMEM);

	/* initialize the lock */
	if ((ret = _pthread_mutex_init(&prwlock->lock, NULL)) != 0) {
		__free(prwlock);
	} else {
		/* initialize the read condition signal */
		ret = _pthread_cond_init(&prwlock->read_signal, NULL);

		if (ret != 0) {
			_pthread_mutex_destroy(&prwlock->lock);
			__free(prwlock);
		} else {
			/* initialize the write condition signal */
			ret = _pthread_cond_init(&prwlock->write_signal, NULL);

			if (ret != 0) {
				_pthread_cond_destroy(&prwlock->read_signal);
				_pthread_mutex_destroy(&prwlock->lock);
				__free(prwlock);
			} else {
				/* success */
				prwlock->state = 0;
				prwlock->blocked_writers = 0;
				*rwlock = prwlock;
			}
		}
	}

	return (ret);
}

#if 0
void
_rwlock_reinit(pthread_rwlock_t prwlock)
{
	_mutex_reinit(&prwlock->lock);
	_cond_reinit(prwlock->read_signal);
	prwlock->state = 0;
	prwlock->blocked_writers = 0;
}
#endif

int
_pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
{
	int ret;

	if (rwlock == NULL) {
		ret = EINVAL;
	} else if (*rwlock == NULL) {
		ret = 0;
	} else {
		pthread_rwlock_t prwlock;

		prwlock = *rwlock;
		rwlock_log("rwlock_destroy %p\n", prwlock);

		_pthread_mutex_destroy(&prwlock->lock);
		_pthread_cond_destroy(&prwlock->read_signal);
		_pthread_cond_destroy(&prwlock->write_signal);
		__free(prwlock);

		*rwlock = NULL;

		ret = 0;
	}
	return (ret);
}

static int
init_static(pthread_t thread, pthread_rwlock_t *rwlock)
{
	int ret;

	THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);

	if (*rwlock == NULL)
		ret = rwlock_init(rwlock, NULL);
	else
		ret = 0;

	THR_LOCK_RELEASE(thread, &_rwlock_static_lock);

	return (ret);
}

int
_pthread_rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
	*rwlock = NULL;
	return (rwlock_init(rwlock, attr));
}

static int
rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
	pthread_t curthread = tls_get_curthread();
	pthread_rwlock_t prwlock;
	int ret;

	if (rwlock == NULL)
		return (EINVAL);

	prwlock = *rwlock;

	/* check for static initialization */
	if (prwlock == NULL) {
		if ((ret = init_static(curthread, rwlock)) != 0)
			return (ret);

		prwlock = *rwlock;
	}
	rwlock_log("rwlock_rdlock_common %p\n", prwlock);

	/* grab the monitor lock */
	if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
		rwlock_log("rwlock_rdlock_common %p (failedA)\n", prwlock);
		return (ret);
	}

	/* check lock count */
	if (prwlock->state == MAX_READ_LOCKS) {
		_pthread_mutex_unlock(&prwlock->lock);
		rwlock_log("rwlock_rdlock_common %p (failedB)\n", prwlock);
		return (EAGAIN);
	}

	curthread = tls_get_curthread();
	if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
		/*
		 * To avoid having to track all the rdlocks held by
		 * a thread or all of the threads that hold a rdlock,
		 * we keep a simple count of all the rdlocks held by
		 * a thread.  If a thread holds any rdlocks it is
		 * possible that it is attempting to take a recursive
		 * rdlock.  If there are blocked writers and precedence
		 * is given to them, then that would result in the thread
		 * deadlocking.  So allowing a thread to take the rdlock
		 * when it already has one or more rdlocks avoids the
		 * deadlock.  I hope the reader can follow that logic ;-)
		 */
		;	/* nothing needed */
	} else {
		/*
		 * Give writers priority over readers
		 *
		 * WARNING: pthread_cond*() temporarily releases the
		 *	    mutex.
		 */
		while (prwlock->blocked_writers || prwlock->state < 0) {
			if (abstime) {
				ret = _pthread_cond_timedwait(
					    &prwlock->read_signal,
					    &prwlock->lock, abstime);
			} else {
				ret = _pthread_cond_wait(
					    &prwlock->read_signal,
					    &prwlock->lock);
			}
			if (ret != 0) {
				/* can't do a whole lot if this fails */
				_pthread_mutex_unlock(&prwlock->lock);
				rwlock_log("rwlock_rdlock_common %p "
					   "(failedC)\n", prwlock);
				return (ret);
			}
		}
	}

	curthread->rdlock_count++;
	prwlock->state++; /* indicate we are locked for reading */

	/*
	 * Something is really wrong if this call fails.  Returning
	 * error won't do because we've already obtained the read
	 * lock.  Decrementing 'state' is no good because we probably
	 * don't have the monitor lock.
	 */
	_pthread_mutex_unlock(&prwlock->lock);
	rwlock_log("rwlock_rdlock_common %p (return %d)\n", prwlock, ret);

	return (ret);
}

int
_pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
	return (rwlock_rdlock_common(rwlock, NULL));
}

int
_pthread_rwlock_timedrdlock (pthread_rwlock_t * __restrict rwlock,
    const struct timespec * __restrict abstime)
{
	return (rwlock_rdlock_common(rwlock, abstime));
}

int
_pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
	pthread_t curthread = tls_get_curthread();
	pthread_rwlock_t prwlock;
	int ret;

	if (rwlock == NULL)
		return (EINVAL);

	prwlock = *rwlock;

	/* check for static initialization */
	if (prwlock == NULL) {
		if ((ret = init_static(curthread, rwlock)) != 0)
			return (ret);

		prwlock = *rwlock;
	}

	/* grab the monitor lock */
	if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
		return (ret);

	curthread = tls_get_curthread();
	if (prwlock->state == MAX_READ_LOCKS)
		ret = EAGAIN;
	else if ((curthread->rdlock_count > 0) && (prwlock->state > 0)) {
		/* see comment for pthread_rwlock_rdlock() */
		curthread->rdlock_count++;
		prwlock->state++;
	}
	/* give writers priority over readers */
	else if (prwlock->blocked_writers || prwlock->state < 0)
		ret = EBUSY;
	else {
		curthread->rdlock_count++;
		prwlock->state++; /* indicate we are locked for reading */
	}

	/* see the comment on this in pthread_rwlock_rdlock */
	_pthread_mutex_unlock(&prwlock->lock);

	return (ret);
}

int
_pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
	pthread_t curthread = tls_get_curthread();
	pthread_rwlock_t prwlock;
	int ret;

	if (rwlock == NULL)
		return (EINVAL);

	prwlock = *rwlock;

	/* check for static initialization */
	if (prwlock == NULL) {
		if ((ret = init_static(curthread, rwlock)) != 0)
			return (ret);

		prwlock = *rwlock;
	}

	/* grab the monitor lock */
	if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
		return (ret);

	if (prwlock->state != 0)
		ret = EBUSY;
	else
		/* indicate we are locked for writing */
		prwlock->state = -1;

	/* see the comment on this in pthread_rwlock_rdlock */
	_pthread_mutex_unlock(&prwlock->lock);

	return (ret);
}

int
_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
	pthread_t curthread;
	pthread_rwlock_t prwlock;
	int ret;

	if (rwlock == NULL)
		return (EINVAL);

	prwlock = *rwlock;

	if (prwlock == NULL)
		return (EINVAL);

	rwlock_log("rwlock_unlock %p\n", prwlock);

	/* grab the monitor lock */
	if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0)
		return (ret);

	curthread = tls_get_curthread();
	if (prwlock->state > 0) {
		/*
		 * Unlock reader
		 */
		curthread->rdlock_count--;
		prwlock->state--;
		if (prwlock->state == 0 && prwlock->blocked_writers)
			ret = _pthread_cond_signal(&prwlock->write_signal);
	} else if (prwlock->state < 0) {
		/*
		 * unlock writer
		 */
		prwlock->state = 0;

		if (prwlock->blocked_writers)
			ret = _pthread_cond_signal(&prwlock->write_signal);
		else
			ret = _pthread_cond_broadcast(&prwlock->read_signal);
	} else {
		ret = EINVAL;
	}

	/* see the comment on this in pthread_rwlock_rdlock */
	_pthread_mutex_unlock(&prwlock->lock);
	rwlock_log("rwlock_unlock %p (return %d)\n", prwlock, ret);

	return (ret);
}

static int
rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
	pthread_t curthread = tls_get_curthread();
	pthread_rwlock_t prwlock;
	int ret;

	if (rwlock == NULL)
		return (EINVAL);

	prwlock = *rwlock;

	/* check for static initialization */
	if (prwlock == NULL) {
		if ((ret = init_static(curthread, rwlock)) != 0)
			return (ret);

		prwlock = *rwlock;
	}
	rwlock_log("rwlock_wrlock_common %p\n", prwlock);

	/* grab the monitor lock */
	if ((ret = _pthread_mutex_lock(&prwlock->lock)) != 0) {
		rwlock_log("rwlock_wrlock_common %p (failedA)\n", prwlock);
		return (ret);
	}

	while (prwlock->state != 0) {
		prwlock->blocked_writers++;

		/*
		 * WARNING: pthread_cond*() temporarily releases the
		 *	    mutex.
		 */
		if (abstime != NULL) {
			ret = _pthread_cond_timedwait(&prwlock->write_signal,
						      &prwlock->lock,
						      abstime);
		} else {
			ret = _pthread_cond_wait(&prwlock->write_signal,
						 &prwlock->lock);
		}

		/*
		 * Undo on failure.  When the blocked_writers count drops
		 * to 0 we may have to wakeup blocked readers.
		 */
		if (ret != 0) {
			prwlock->blocked_writers--;
			if (prwlock->blocked_writers == 0 &&
			    prwlock->state >= 0) {
				_pthread_cond_broadcast(&prwlock->read_signal);
			}
			_pthread_mutex_unlock(&prwlock->lock);
			rwlock_log("rwlock_wrlock_common %p (failedB %d)\n",
				   prwlock, ret);
			return (ret);
		}

		prwlock->blocked_writers--;
	}

	/* indicate we are locked for writing */
	prwlock->state = -1;

	/* see the comment on this in pthread_rwlock_rdlock */
	_pthread_mutex_unlock(&prwlock->lock);
	rwlock_log("rwlock_wrlock_common %p (returns %d)\n", prwlock, ret);

	return (ret);
}

int
_pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
	return (rwlock_wrlock_common (rwlock, NULL));
}

int
_pthread_rwlock_timedwrlock (pthread_rwlock_t * __restrict rwlock,
    const struct timespec * __restrict abstime)
{
	return (rwlock_wrlock_common (rwlock, abstime));
}

__strong_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
__strong_reference(_pthread_rwlock_init, pthread_rwlock_init);
__strong_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
__strong_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
__strong_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
__strong_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
__strong_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
__strong_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
__strong_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);