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/* Copyright (C) 2000 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/* Synchronization - readers / writer thread locks */
#include "mysys_priv.h"
#if defined(THREAD)
#if defined(NEED_MY_RW_LOCK)
#include <errno.h>
/*
Source base from Sun Microsystems SPILT, simplified for MySQL use
-- Joshua Chamas
Some cleanup and additional code by Monty
*/
/*
* Multithreaded Demo Source
*
* Copyright (C) 1995 by Sun Microsystems, Inc.
* All rights reserved.
*
* This file is a product of SunSoft, Inc. and is provided for
* unrestricted use provided that this legend is included on all
* media and as a part of the software program in whole or part.
* Users may copy, modify or distribute this file at will.
*
* THIS FILE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
* THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR
* PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE.
*
* This file is provided with no support and without any obligation on the
* part of SunSoft, Inc. to assist in its use, correction, modification or
* enhancement.
*
* SUNSOFT AND SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT
* TO THE INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS
* FILE OR ANY PART THEREOF.
*
* IN NO EVENT WILL SUNSOFT OR SUN MICROSYSTEMS, INC. BE LIABLE FOR ANY
* LOST REVENUE OR PROFITS OR OTHER SPECIAL, INDIRECT AND CONSEQUENTIAL
* DAMAGES, EVEN IF THEY HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGES.
*
* SunSoft, Inc.
* 2550 Garcia Avenue
* Mountain View, California 94043
*/
int my_rw_init(my_rw_lock_t *rwp, my_bool *prefer_readers_attr)
{
pthread_condattr_t cond_attr;
pthread_mutex_init( &rwp->lock, MY_MUTEX_INIT_FAST);
pthread_condattr_init( &cond_attr );
pthread_cond_init( &rwp->readers, &cond_attr );
pthread_cond_init( &rwp->writers, &cond_attr );
pthread_condattr_destroy(&cond_attr);
rwp->state = 0;
rwp->waiters = 0;
#ifdef SAFE_MUTEX
rwp->write_thread = 0;
#endif
/* If attribute argument is NULL use default value - prefer writers. */
rwp->prefer_readers= prefer_readers_attr ? *prefer_readers_attr : FALSE;
return(0);
}
int my_rw_destroy(my_rw_lock_t *rwp)
{
DBUG_ASSERT(rwp->state == 0);
pthread_mutex_destroy( &rwp->lock );
pthread_cond_destroy( &rwp->readers );
pthread_cond_destroy( &rwp->writers );
return(0);
}
int my_rw_rdlock(my_rw_lock_t *rwp)
{
pthread_mutex_lock(&rwp->lock);
/* active or queued writers */
while (( rwp->state < 0 ) ||
(rwp->waiters && ! rwp->prefer_readers))
pthread_cond_wait( &rwp->readers, &rwp->lock);
rwp->state++;
pthread_mutex_unlock(&rwp->lock);
return(0);
}
int my_rw_tryrdlock(my_rw_lock_t *rwp)
{
int res;
pthread_mutex_lock(&rwp->lock);
if ((rwp->state < 0 ) ||
(rwp->waiters && ! rwp->prefer_readers))
res= EBUSY; /* Can't get lock */
else
{
res=0;
rwp->state++;
}
pthread_mutex_unlock(&rwp->lock);
return(res);
}
int my_rw_wrlock(my_rw_lock_t *rwp)
{
pthread_mutex_lock(&rwp->lock);
rwp->waiters++; /* another writer queued */
my_rw_lock_assert_not_write_owner(rwp);
while (rwp->state)
pthread_cond_wait(&rwp->writers, &rwp->lock);
rwp->state = -1;
rwp->waiters--;
#ifdef SAFE_MUTEX
rwp->write_thread= pthread_self();
#endif
pthread_mutex_unlock(&rwp->lock);
return(0);
}
int my_rw_trywrlock(my_rw_lock_t *rwp)
{
int res;
pthread_mutex_lock(&rwp->lock);
if (rwp->state)
res= EBUSY; /* Can't get lock */
else
{
res=0;
rwp->state = -1;
#ifdef SAFE_MUTEX
rwp->write_thread= pthread_self();
#endif
}
pthread_mutex_unlock(&rwp->lock);
return(res);
}
int my_rw_unlock(my_rw_lock_t *rwp)
{
DBUG_PRINT("rw_unlock",
("state: %d waiters: %d", rwp->state, rwp->waiters));
pthread_mutex_lock(&rwp->lock);
DBUG_ASSERT(rwp->state != 0);
if (rwp->state == -1) /* writer releasing */
{
my_rw_lock_assert_write_owner(rwp);
rwp->state= 0; /* mark as available */
#ifdef SAFE_MUTEX
rwp->write_thread= 0;
#endif
if ( rwp->waiters ) /* writers queued */
pthread_cond_signal( &rwp->writers );
else
pthread_cond_broadcast( &rwp->readers );
}
else
{
if ( --rwp->state == 0 && /* no more readers */
rwp->waiters)
pthread_cond_signal( &rwp->writers );
}
pthread_mutex_unlock( &rwp->lock );
return(0);
}
int rw_pr_init(struct st_my_rw_lock_t *rwlock)
{
my_bool prefer_readers_attr= TRUE;
return my_rw_init(rwlock, &prefer_readers_attr);
}
#else
/*
We are on system which has native read/write locks which support
preferring of readers.
*/
int rw_pr_init(rw_pr_lock_t *rwlock)
{
pthread_rwlockattr_t rwlock_attr;
pthread_rwlockattr_init(&rwlock_attr);
pthread_rwlockattr_setkind_np(&rwlock_attr, PTHREAD_RWLOCK_PREFER_READER_NP);
pthread_rwlock_init(rwlock, NULL);
pthread_rwlockattr_destroy(&rwlock_attr);
return 0;
}
#endif /* defined(NEED_MY_RW_LOCK) */
#endif /* defined(THREAD) */
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