freebsd-dev/lib/libthr/thread/thr_rwlock.c
2008-04-14 08:08:40 +00:00

379 lines
9.2 KiB
C

/*-
* 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.
*
* $FreeBSD$
*/
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include "namespace.h"
#include <pthread.h>
#include "un-namespace.h"
#include "thr_private.h"
__weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
__weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
__weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
__weak_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
__weak_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
__weak_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
__weak_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
__weak_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
__weak_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);
/*
* Prototypes
*/
static int
rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
{
pthread_rwlock_t prwlock;
prwlock = (pthread_rwlock_t)calloc(1, sizeof(struct pthread_rwlock));
if (prwlock == NULL)
return (ENOMEM);
*rwlock = prwlock;
return (0);
}
int
_pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
{
int ret;
if (rwlock == NULL)
ret = EINVAL;
else {
pthread_rwlock_t prwlock;
prwlock = *rwlock;
*rwlock = NULL;
free(prwlock);
ret = 0;
}
return (ret);
}
static int
init_static(struct pthread *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)
{
struct pthread *curthread = _get_curthread();
pthread_rwlock_t prwlock;
struct timespec ts, ts2, *tsp;
int flags;
int ret;
if (__predict_false(rwlock == NULL))
return (EINVAL);
prwlock = *rwlock;
/* check for static initialization */
if (__predict_false(prwlock == NULL)) {
if ((ret = init_static(curthread, rwlock)) != 0)
return (ret);
prwlock = *rwlock;
}
if (curthread->rdlock_count) {
/*
* 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 ;-)
*/
flags = URWLOCK_PREFER_READER;
} else {
flags = 0;
}
/*
* POSIX said the validity of the abstimeout parameter need
* not be checked if the lock can be immediately acquired.
*/
ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
if (ret == 0) {
curthread->rdlock_count++;
return (ret);
}
if (__predict_false(abstime &&
(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
return (EINVAL);
for (;;) {
if (abstime) {
clock_gettime(CLOCK_REALTIME, &ts);
TIMESPEC_SUB(&ts2, abstime, &ts);
if (ts2.tv_sec < 0 ||
(ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
return (ETIMEDOUT);
tsp = &ts2;
} else
tsp = NULL;
/* goto kernel and lock it */
ret = __thr_rwlock_rdlock(&prwlock->lock, flags, tsp);
if (ret != EINTR)
break;
/* if interrupted, try to lock it in userland again. */
if (_thr_rwlock_tryrdlock(&prwlock->lock, flags) == 0) {
ret = 0;
curthread->rdlock_count++;
break;
}
}
return (ret);
}
int
_pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
return (rwlock_rdlock_common(rwlock, NULL));
}
int
_pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
const struct timespec *abstime)
{
return (rwlock_rdlock_common(rwlock, abstime));
}
int
_pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
struct pthread *curthread = _get_curthread();
pthread_rwlock_t prwlock;
int flags;
int ret;
if (__predict_false(rwlock == NULL))
return (EINVAL);
prwlock = *rwlock;
/* check for static initialization */
if (__predict_false(prwlock == NULL)) {
if ((ret = init_static(curthread, rwlock)) != 0)
return (ret);
prwlock = *rwlock;
}
if (curthread->rdlock_count) {
/*
* 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 ;-)
*/
flags = URWLOCK_PREFER_READER;
} else {
flags = 0;
}
ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
if (ret == 0)
curthread->rdlock_count++;
return (ret);
}
int
_pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
struct pthread *curthread = _get_curthread();
pthread_rwlock_t prwlock;
int ret;
if (__predict_false(rwlock == NULL))
return (EINVAL);
prwlock = *rwlock;
/* check for static initialization */
if (__predict_false(prwlock == NULL)) {
if ((ret = init_static(curthread, rwlock)) != 0)
return (ret);
prwlock = *rwlock;
}
ret = _thr_rwlock_trywrlock(&prwlock->lock);
if (ret == 0)
prwlock->owner = curthread;
return (ret);
}
static int
rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
{
struct pthread *curthread = _get_curthread();
pthread_rwlock_t prwlock;
struct timespec ts, ts2, *tsp;
int ret;
if (__predict_false(rwlock == NULL))
return (EINVAL);
prwlock = *rwlock;
/* check for static initialization */
if (__predict_false(prwlock == NULL)) {
if ((ret = init_static(curthread, rwlock)) != 0)
return (ret);
prwlock = *rwlock;
}
/*
* POSIX said the validity of the abstimeout parameter need
* not be checked if the lock can be immediately acquired.
*/
ret = _thr_rwlock_trywrlock(&prwlock->lock);
if (ret == 0) {
prwlock->owner = curthread;
return (ret);
}
if (__predict_false(abstime &&
(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
return (EINVAL);
for (;;) {
if (abstime != NULL) {
clock_gettime(CLOCK_REALTIME, &ts);
TIMESPEC_SUB(&ts2, abstime, &ts);
if (ts2.tv_sec < 0 ||
(ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
return (ETIMEDOUT);
tsp = &ts2;
} else
tsp = NULL;
/* goto kernel and lock it */
ret = __thr_rwlock_wrlock(&prwlock->lock, tsp);
if (ret == 0) {
prwlock->owner = curthread;
break;
}
if (ret != EINTR)
break;
/* if interrupted, try to lock it in userland again. */
if (_thr_rwlock_trywrlock(&prwlock->lock) == 0) {
ret = 0;
prwlock->owner = curthread;
break;
}
}
return (ret);
}
int
_pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
return (rwlock_wrlock_common (rwlock, NULL));
}
int
_pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
const struct timespec *abstime)
{
return (rwlock_wrlock_common (rwlock, abstime));
}
int
_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
struct pthread *curthread = _get_curthread();
pthread_rwlock_t prwlock;
int ret;
int32_t state;
if (__predict_false(rwlock == NULL))
return (EINVAL);
prwlock = *rwlock;
if (__predict_false(prwlock == NULL))
return (EINVAL);
state = prwlock->lock.rw_state;
if (state & URWLOCK_WRITE_OWNER) {
if (__predict_false(prwlock->owner != curthread))
return (EPERM);
prwlock->owner = NULL;
}
ret = _thr_rwlock_unlock(&prwlock->lock);
if (ret == 0 && (state & URWLOCK_WRITE_OWNER) == 0)
curthread->rdlock_count--;
return (ret);
}