de1e74c6a5
a silly rwlock deadlock problem, the deadlock is caused by writer waiters, if a thread has already locked a reader lock, and wants to acquire another reader lock, it will be blocked by writer waiters, but we had already fixed it years ago.
347 lines
8.7 KiB
C
347 lines
8.7 KiB
C
/*-
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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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* $FreeBSD$
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*/
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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 "namespace.h"
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#include <pthread.h>
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#include "un-namespace.h"
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#include "thr_private.h"
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__weak_reference(_pthread_rwlock_destroy, pthread_rwlock_destroy);
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__weak_reference(_pthread_rwlock_init, pthread_rwlock_init);
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__weak_reference(_pthread_rwlock_rdlock, pthread_rwlock_rdlock);
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__weak_reference(_pthread_rwlock_timedrdlock, pthread_rwlock_timedrdlock);
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__weak_reference(_pthread_rwlock_tryrdlock, pthread_rwlock_tryrdlock);
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__weak_reference(_pthread_rwlock_trywrlock, pthread_rwlock_trywrlock);
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__weak_reference(_pthread_rwlock_unlock, pthread_rwlock_unlock);
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__weak_reference(_pthread_rwlock_wrlock, pthread_rwlock_wrlock);
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__weak_reference(_pthread_rwlock_timedwrlock, pthread_rwlock_timedwrlock);
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#define CHECK_AND_INIT_RWLOCK \
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if (__predict_false((prwlock = (*rwlock)) <= THR_RWLOCK_DESTROYED)) { \
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if (prwlock == THR_RWLOCK_INITIALIZER) { \
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int ret; \
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ret = init_static(_get_curthread(), rwlock); \
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if (ret) \
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return (ret); \
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} else if (prwlock == THR_RWLOCK_DESTROYED) { \
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return (EINVAL); \
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} \
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prwlock = *rwlock; \
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}
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/*
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* Prototypes
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*/
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static int
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rwlock_init(pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr __unused)
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{
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pthread_rwlock_t prwlock;
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prwlock = (pthread_rwlock_t)calloc(1, sizeof(struct pthread_rwlock));
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if (prwlock == NULL)
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return (ENOMEM);
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*rwlock = prwlock;
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return (0);
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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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pthread_rwlock_t prwlock;
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int ret;
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prwlock = *rwlock;
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if (prwlock == THR_RWLOCK_INITIALIZER)
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ret = 0;
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else if (prwlock == THR_RWLOCK_DESTROYED)
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ret = EINVAL;
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else {
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*rwlock = THR_RWLOCK_DESTROYED;
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free(prwlock);
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ret = 0;
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}
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return (ret);
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}
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static int
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init_static(struct pthread *thread, pthread_rwlock_t *rwlock)
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{
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int ret;
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THR_LOCK_ACQUIRE(thread, &_rwlock_static_lock);
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if (*rwlock == THR_RWLOCK_INITIALIZER)
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ret = rwlock_init(rwlock, NULL);
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else
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ret = 0;
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THR_LOCK_RELEASE(thread, &_rwlock_static_lock);
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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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*rwlock = NULL;
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return (rwlock_init(rwlock, attr));
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}
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static int
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rwlock_rdlock_common(pthread_rwlock_t *rwlock, const struct timespec *abstime)
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{
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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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struct timespec ts, ts2, *tsp;
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int flags;
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int ret;
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CHECK_AND_INIT_RWLOCK
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if (curthread->rdlock_count) {
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/*
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* To avoid having to track all the rdlocks held by
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* a thread or all of the threads that hold a rdlock,
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* we keep a simple count of all the rdlocks held by
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* a thread. If a thread holds any rdlocks it is
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* possible that it is attempting to take a recursive
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* rdlock. If there are blocked writers and precedence
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* is given to them, then that would result in the thread
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* deadlocking. So allowing a thread to take the rdlock
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* when it already has one or more rdlocks avoids the
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* deadlock. I hope the reader can follow that logic ;-)
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*/
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flags = URWLOCK_PREFER_READER;
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} else {
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flags = 0;
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}
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/*
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* POSIX said the validity of the abstimeout parameter need
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* not be checked if the lock can be immediately acquired.
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*/
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ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
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if (ret == 0) {
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curthread->rdlock_count++;
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return (ret);
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}
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if (__predict_false(abstime &&
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(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
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return (EINVAL);
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for (;;) {
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if (abstime) {
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clock_gettime(CLOCK_REALTIME, &ts);
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TIMESPEC_SUB(&ts2, abstime, &ts);
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if (ts2.tv_sec < 0 ||
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(ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
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return (ETIMEDOUT);
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tsp = &ts2;
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} else
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tsp = NULL;
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/* goto kernel and lock it */
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ret = __thr_rwlock_rdlock(&prwlock->lock, flags, tsp);
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if (ret != EINTR)
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break;
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/* if interrupted, try to lock it in userland again. */
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if (_thr_rwlock_tryrdlock(&prwlock->lock, flags) == 0) {
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ret = 0;
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break;
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}
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}
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if (ret == 0)
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curthread->rdlock_count++;
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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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return (rwlock_rdlock_common(rwlock, NULL));
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}
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int
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_pthread_rwlock_timedrdlock (pthread_rwlock_t *rwlock,
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const struct timespec *abstime)
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{
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return (rwlock_rdlock_common(rwlock, abstime));
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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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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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int flags;
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int ret;
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CHECK_AND_INIT_RWLOCK
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if (curthread->rdlock_count) {
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/*
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* To avoid having to track all the rdlocks held by
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* a thread or all of the threads that hold a rdlock,
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* we keep a simple count of all the rdlocks held by
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* a thread. If a thread holds any rdlocks it is
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* possible that it is attempting to take a recursive
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* rdlock. If there are blocked writers and precedence
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* is given to them, then that would result in the thread
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* deadlocking. So allowing a thread to take the rdlock
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* when it already has one or more rdlocks avoids the
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* deadlock. I hope the reader can follow that logic ;-)
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*/
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flags = URWLOCK_PREFER_READER;
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} else {
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flags = 0;
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}
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ret = _thr_rwlock_tryrdlock(&prwlock->lock, flags);
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if (ret == 0)
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curthread->rdlock_count++;
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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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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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int ret;
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CHECK_AND_INIT_RWLOCK
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ret = _thr_rwlock_trywrlock(&prwlock->lock);
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if (ret == 0)
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prwlock->owner = curthread;
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return (ret);
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}
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static int
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rwlock_wrlock_common (pthread_rwlock_t *rwlock, const struct timespec *abstime)
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{
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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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struct timespec ts, ts2, *tsp;
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int ret;
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CHECK_AND_INIT_RWLOCK
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/*
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* POSIX said the validity of the abstimeout parameter need
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* not be checked if the lock can be immediately acquired.
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*/
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ret = _thr_rwlock_trywrlock(&prwlock->lock);
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if (ret == 0) {
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prwlock->owner = curthread;
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return (ret);
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}
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if (__predict_false(abstime &&
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(abstime->tv_nsec >= 1000000000 || abstime->tv_nsec < 0)))
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return (EINVAL);
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for (;;) {
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if (abstime != NULL) {
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clock_gettime(CLOCK_REALTIME, &ts);
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TIMESPEC_SUB(&ts2, abstime, &ts);
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if (ts2.tv_sec < 0 ||
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(ts2.tv_sec == 0 && ts2.tv_nsec <= 0))
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return (ETIMEDOUT);
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tsp = &ts2;
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} else
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tsp = NULL;
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/* goto kernel and lock it */
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ret = __thr_rwlock_wrlock(&prwlock->lock, tsp);
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if (ret == 0) {
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prwlock->owner = curthread;
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break;
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}
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if (ret != EINTR)
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break;
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/* if interrupted, try to lock it in userland again. */
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if (_thr_rwlock_trywrlock(&prwlock->lock) == 0) {
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ret = 0;
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prwlock->owner = curthread;
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break;
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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_wrlock (pthread_rwlock_t *rwlock)
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{
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return (rwlock_wrlock_common (rwlock, NULL));
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}
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int
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_pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
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const struct timespec *abstime)
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{
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return (rwlock_wrlock_common (rwlock, abstime));
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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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struct pthread *curthread = _get_curthread();
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pthread_rwlock_t prwlock;
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int ret;
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int32_t state;
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prwlock = *rwlock;
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if (__predict_false(prwlock <= THR_RWLOCK_DESTROYED))
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return (EINVAL);
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state = prwlock->lock.rw_state;
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if (state & URWLOCK_WRITE_OWNER) {
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if (__predict_false(prwlock->owner != curthread))
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return (EPERM);
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prwlock->owner = NULL;
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}
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ret = _thr_rwlock_unlock(&prwlock->lock);
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if (ret == 0 && (state & URWLOCK_WRITE_OWNER) == 0)
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curthread->rdlock_count--;
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return (ret);
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}
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