FreeBSD-5.3/lib/libthr/thread/thr_rwlock.c
/*-
* Copyright (c) 1998 Alex Nash
* Copyright (c) 2004 Michael Telahun Makonnen
* 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/libthr/thread/thr_rwlock.c,v 1.7 2004/07/30 17:13:00 mtm Exp $
*/
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <pthread.h>
#include "thr_private.h"
/* maximum number of times a read lock may be obtained */
#define MAX_READ_LOCKS (INT_MAX - 1)
/*
* For distinguishing operations on read and write locks.
*/
enum rwlock_type {RWT_READ, RWT_WRITE};
/* Support for staticaly initialized mutexes. */
static struct umtx init_lock = UMTX_INITIALIZER;
__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_timedwrlock, pthread_rwlock_timedwrlock);
__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);
static int insert_rwlock(struct pthread_rwlock *, enum rwlock_type);
static int rwlock_init_static(struct pthread_rwlock **rwlock);
static int rwlock_rdlock_common(pthread_rwlock_t *, int,
const struct timespec *);
static int rwlock_wrlock_common(pthread_rwlock_t *, int,
const struct timespec *);
int
_pthread_rwlock_destroy (pthread_rwlock_t *rwlock)
{
pthread_rwlock_t prwlock;
if (rwlock == NULL || *rwlock == NULL)
return (EINVAL);
prwlock = *rwlock;
if (prwlock->state != 0)
return (EBUSY);
pthread_mutex_destroy(&prwlock->lock);
pthread_cond_destroy(&prwlock->read_signal);
pthread_cond_destroy(&prwlock->write_signal);
free(prwlock);
*rwlock = NULL;
return (0);
}
int
_pthread_rwlock_init (pthread_rwlock_t *rwlock, const pthread_rwlockattr_t *attr)
{
pthread_rwlock_t prwlock;
int ret;
/* allocate rwlock object */
prwlock = (pthread_rwlock_t)malloc(sizeof(struct pthread_rwlock));
if (prwlock == NULL) {
ret = ENOMEM;
goto out;
}
/* initialize the lock */
if ((ret = pthread_mutex_init(&prwlock->lock, NULL)) != 0)
goto out;
/* initialize the read condition signal */
if ((ret = pthread_cond_init(&prwlock->read_signal, NULL)) != 0)
goto out_readcond;
/* initialize the write condition signal */
if ((ret = pthread_cond_init(&prwlock->write_signal, NULL)) != 0)
goto out_writecond;
/* success */
prwlock->state = 0;
prwlock->blocked_writers = 0;
*rwlock = prwlock;
return (0);
out_writecond:
pthread_cond_destroy(&prwlock->read_signal);
out_readcond:
pthread_mutex_destroy(&prwlock->lock);
out:
if (prwlock != NULL)
free(prwlock);
return(ret);
}
/*
* If nonblocking is 0 this function will wait on the lock. If
* it is greater than 0 it will return immediately with EBUSY.
*/
static int
rwlock_rdlock_common(pthread_rwlock_t *rwlock, int nonblocking,
const struct timespec *timeout)
{
struct rwlock_held *rh;
pthread_rwlock_t prwlock;
int ret;
rh = NULL;
if (rwlock == NULL)
return(EINVAL);
/*
* Check for validity of the timeout parameter.
*/
if (timeout != NULL &&
(timeout->tv_nsec < 0 || timeout->tv_nsec >= 1000000000))
return (EINVAL);
if ((ret = rwlock_init_static(rwlock)) !=0 )
return (ret);
prwlock = *rwlock;
/* grab the monitor lock */
if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
return(ret);
/* check lock count */
if (prwlock->state == MAX_READ_LOCKS) {
pthread_mutex_unlock(&prwlock->lock);
return (EAGAIN);
}
/* give writers priority over readers */
while (prwlock->blocked_writers || prwlock->state < 0) {
if (nonblocking) {
pthread_mutex_unlock(&prwlock->lock);
return (EBUSY);
}
/*
* If this lock is already held for writing we have
* a deadlock situation.
*/
if (curthread->rwlockList != NULL && prwlock->state < 0) {
LIST_FOREACH(rh, curthread->rwlockList, rh_link) {
if (rh->rh_rwlock == prwlock &&
rh->rh_wrcount > 0) {
pthread_mutex_unlock(&prwlock->lock);
return (EDEADLK);
}
}
}
if (timeout == NULL)
ret = pthread_cond_wait(&prwlock->read_signal,
&prwlock->lock);
else
ret = pthread_cond_timedwait(&prwlock->read_signal,
&prwlock->lock, timeout);
if (ret != 0 && ret != EINTR) {
/* can't do a whole lot if this fails */
pthread_mutex_unlock(&prwlock->lock);
return(ret);
}
}
++prwlock->state; /* indicate we are locked for reading */
ret = insert_rwlock(prwlock, RWT_READ);
if (ret != 0) {
pthread_mutex_unlock(&prwlock->lock);
return (ret);
}
/*
* 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);
return(0);
}
int
_pthread_rwlock_rdlock (pthread_rwlock_t *rwlock)
{
return (rwlock_rdlock_common(rwlock, 0, NULL));
}
int
_pthread_rwlock_timedrdlock(pthread_rwlock_t *rwlock,
const struct timespec *timeout)
{
return (rwlock_rdlock_common(rwlock, 0, timeout));
}
int
_pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock)
{
return (rwlock_rdlock_common(rwlock, 1, NULL));
}
int
_pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
struct rwlock_held *rh;
pthread_rwlock_t prwlock;
int ret;
rh = NULL;
if (rwlock == NULL || *rwlock == NULL)
return(EINVAL);
prwlock = *rwlock;
/* grab the monitor lock */
if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
return(ret);
if (curthread->rwlockList != NULL) {
LIST_FOREACH(rh, curthread->rwlockList, rh_link) {
if (rh->rh_rwlock == prwlock)
break;
}
}
if (rh == NULL) {
ret = EPERM;
goto out;
}
if (prwlock->state > 0) {
PTHREAD_ASSERT(rh->rh_wrcount == 0,
"write count on a readlock should be zero!");
rh->rh_rdcount--;
if (--prwlock->state == 0 && prwlock->blocked_writers)
ret = pthread_cond_signal(&prwlock->write_signal);
} else if (prwlock->state < 0) {
PTHREAD_ASSERT(rh->rh_rdcount == 0,
"read count on a writelock should be zero!");
rh->rh_wrcount--;
prwlock->state = 0;
if (prwlock->blocked_writers)
ret = pthread_cond_signal(&prwlock->write_signal);
else
ret = pthread_cond_broadcast(&prwlock->read_signal);
} else {
/*
* No thread holds this lock. We should never get here.
*/
PTHREAD_ASSERT(0, "state=0 on read-write lock held by thread");
ret = EPERM;
goto out;
}
if (rh->rh_wrcount == 0 && rh->rh_rdcount == 0) {
LIST_REMOVE(rh, rh_link);
free(rh);
}
out:
/* see the comment on this in rwlock_rdlock_common */
pthread_mutex_unlock(&prwlock->lock);
return(ret);
}
int
_pthread_rwlock_wrlock (pthread_rwlock_t *rwlock)
{
return (rwlock_wrlock_common(rwlock, 0, NULL));
}
int
_pthread_rwlock_timedwrlock (pthread_rwlock_t *rwlock,
const struct timespec *timeout)
{
return (rwlock_wrlock_common(rwlock, 0, timeout));
}
int
_pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock)
{
return (rwlock_wrlock_common(rwlock, 1, NULL));
}
/*
* If nonblocking is 0 this function will wait on the lock. If
* it is greater than 0 it will return immediately with EBUSY.
*/
static int
rwlock_wrlock_common(pthread_rwlock_t *rwlock, int nonblocking,
const struct timespec *timeout)
{
struct rwlock_held *rh;
pthread_rwlock_t prwlock;
int ret;
rh = NULL;
if (rwlock == NULL)
return(EINVAL);
/*
* Check the timeout value for validity.
*/
if (timeout != NULL &&
(timeout->tv_nsec < 0 || timeout->tv_nsec >= 1000000000))
return (EINVAL);
if ((ret = rwlock_init_static(rwlock)) !=0 )
return (ret);
prwlock = *rwlock;
/* grab the monitor lock */
if ((ret = pthread_mutex_lock(&prwlock->lock)) != 0)
return(ret);
while (prwlock->state != 0) {
if (nonblocking) {
pthread_mutex_unlock(&prwlock->lock);
return (EBUSY);
}
/*
* If this thread already holds the lock for reading
* or writing we have a deadlock situation.
*/
if (curthread->rwlockList != NULL) {
LIST_FOREACH(rh, curthread->rwlockList, rh_link) {
if (rh->rh_rwlock == prwlock) {
PTHREAD_ASSERT((rh->rh_rdcount > 0 ||
rh->rh_wrcount > 0),
"Invalid 0 R/RW count!");
pthread_mutex_unlock(&prwlock->lock);
return (EDEADLK);
break;
}
}
}
++prwlock->blocked_writers;
if (timeout == NULL)
ret = pthread_cond_wait(&prwlock->write_signal,
&prwlock->lock);
else
ret = pthread_cond_timedwait(&prwlock->write_signal,
&prwlock->lock, timeout);
if (ret != 0 && ret != EINTR) {
--prwlock->blocked_writers;
pthread_mutex_unlock(&prwlock->lock);
return(ret);
}
--prwlock->blocked_writers;
}
/* indicate we are locked for writing */
prwlock->state = -1;
ret = insert_rwlock(prwlock, RWT_WRITE);
if (ret != 0) {
pthread_mutex_unlock(&prwlock->lock);
return (ret);
}
/* see the comment on this in pthread_rwlock_rdlock */
pthread_mutex_unlock(&prwlock->lock);
return(0);
}
static int
insert_rwlock(struct pthread_rwlock *prwlock, enum rwlock_type rwt)
{
struct rwlock_held *rh;
/*
* Initialize the rwlock list in the thread. Although this function
* may be called for many read-write locks, the initialization
* of the the head happens only once during the lifetime of
* the thread.
*/
if (curthread->rwlockList == NULL) {
curthread->rwlockList =
(struct rwlock_listhead *)malloc(sizeof(struct rwlock_listhead));
if (curthread->rwlockList == NULL) {
return (ENOMEM);
}
LIST_INIT(curthread->rwlockList);
}
LIST_FOREACH(rh, curthread->rwlockList, rh_link) {
if (rh->rh_rwlock == prwlock) {
if (rwt == RWT_READ)
rh->rh_rdcount++;
else if (rwt == RWT_WRITE)
rh->rh_wrcount++;
return (0);
}
}
/*
* This is the first time we're holding this lock,
* create a new entry.
*/
rh = (struct rwlock_held *)malloc(sizeof(struct rwlock_held));
if (rh == NULL)
return (ENOMEM);
rh->rh_rwlock = prwlock;
rh->rh_rdcount = 0;
rh->rh_wrcount = 0;
if (rwt == RWT_READ)
rh->rh_rdcount = 1;
else if (rwt == RWT_WRITE)
rh->rh_wrcount = 1;
LIST_INSERT_HEAD(curthread->rwlockList, rh, rh_link);
return (0);
}
/*
* There are consumers of rwlocks, inluding our own libc, that depend on
* a PTHREAD_RWLOCK_INITIALIZER to do for rwlocks what
* a similarly named symbol does for statically initialized mutexes.
* This symbol was dropped in The Open Group Base Specifications Issue 6
* and does not exist in IEEE Std 1003.1, 2003, but it should still be
* supported for backwards compatibility.
*/
static int
rwlock_init_static(struct pthread_rwlock **rwlock)
{
int error;
error = 0;
UMTX_LOCK(&init_lock);
if (*rwlock == PTHREAD_RWLOCK_INITIALIZER)
error = _pthread_rwlock_init(rwlock, NULL);
UMTX_UNLOCK(&init_lock);
return (error);
}