mariadb/mysys/thr_rwlock.c
Dmitry Lenev 6b5c4a9ef6 Fix for bug #51105 "MDL deadlock in rqg_mdl_stability test
on Windows".

On platforms where read-write lock implementation does not
prefer readers by default (Windows, Solaris) server might
have deadlocked while detecting MDL deadlock.

MDL deadlock detector relies on the fact that read-write
locks which are used in its implementation prefer readers
(see new comment for MDL_lock::m_rwlock for details).
So far MDL code assumed that default implementation of
read/write locks for the system has this property.
Indeed, this turned out ot be wrong, for example, for
Windows or Solaris. Thus MDL deadlock detector might have
deadlocked on these systems.

This fix simply adds portable implementation of read/write
lock which prefer readers and changes MDL code to use this
new type of synchronization primitive.

No test case is added as existing rqg_mdl_stability test can
serve as one.

config.h.cmake:
  Check for presence of pthread_rwlockattr_setkind_np to be
  able to determine if system natively supports read-write
  locks for which we can specify if readers or writers should
  be preferred.
configure.cmake:
  Check for presence of pthread_rwlockattr_setkind_np to be
  able to determine if system natively supports read-write
  locks for which we can specify if readers or writers should
  be preferred.
configure.in:
  Check for presence of pthread_rwlockattr_setkind_np to be
  able to determine if system natively supports read-write
  locks for which we can specify if readers or writers should
  be preferred.
include/my_pthread.h:
  Added support for portable read-write locks which prefer
  readers.
  To do so extended existing my_rw_lock_t implementation to
  support selection of whom to prefer depending on a flag.
mysys/thr_rwlock.c:
  Extended existing my_rw_lock_t implementation to support
  selection of whom to prefer depending on a flag.
  Added rw_pr_init() function implementing initialization of
  read-write locks preferring readers.
sql/mdl.cc:
  Use portable read-write locks which prefer readers instead of
  relying on that system implementation of read-write locks has
  this property (this was true for Linux/NPTL but was false,
  for example, for Windows and Solaris).
  Added comment explaining why preferring readers is important
  for MDL deadlock detector (thanks to Serg for example!).
sql/mdl.h:
  Use portable read-write locks which prefer readers instead of
  relying on that system implementation of read-write locks has
  this property (this was true for Linux/NPTL but was false,
  for example, for Windows and Solaris).
2010-02-28 07:35:09 +03:00

203 lines
5.2 KiB
C

/* 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;
/* 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)
{
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 */
while (rwp->state)
pthread_cond_wait(&rwp->writers, &rwp->lock);
rwp->state = -1;
rwp->waiters--;
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;
}
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);
if (rwp->state == -1) /* writer releasing */
{
rwp->state= 0; /* mark as available */
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) */