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-rw-r--r--mysys/thr_rwlock.c377
1 files changed, 377 insertions, 0 deletions
diff --git a/mysys/thr_rwlock.c b/mysys/thr_rwlock.c
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+++ b/mysys/thr_rwlock.c
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+/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
+
+ 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
+
+/* Synchronization - readers / writer thread locks */
+
+#include "mysys_priv.h"
+#if defined(NEED_MY_RW_LOCK)
+#include <errno.h>
+
+#ifdef _WIN32
+
+int my_rw_init(my_rw_lock_t *rwp)
+{
+ InitializeSRWLock(&rwp->srwlock);
+ rwp->have_exclusive_srwlock = FALSE;
+ return 0;
+}
+
+
+int my_rw_rdlock(my_rw_lock_t *rwp)
+{
+ AcquireSRWLockShared(&rwp->srwlock);
+ return 0;
+}
+
+
+int my_rw_tryrdlock(my_rw_lock_t *rwp)
+{
+ if (!TryAcquireSRWLockShared(&rwp->srwlock))
+ return EBUSY;
+ return 0;
+}
+
+
+int my_rw_wrlock(my_rw_lock_t *rwp)
+{
+ AcquireSRWLockExclusive(&rwp->srwlock);
+ rwp->have_exclusive_srwlock= TRUE;
+ return 0;
+}
+
+int my_rw_trywrlock(my_rw_lock_t *rwp)
+{
+ if (!TryAcquireSRWLockExclusive(&rwp->srwlock))
+ return EBUSY;
+ rwp->have_exclusive_srwlock= TRUE;
+ return 0;
+}
+
+
+int my_rw_unlock(my_rw_lock_t *rwp)
+{
+ if (rwp->have_exclusive_srwlock)
+ {
+ rwp->have_exclusive_srwlock= FALSE;
+ ReleaseSRWLockExclusive(&rwp->srwlock);
+ }
+ else
+ {
+ ReleaseSRWLockShared(&rwp->srwlock);
+ }
+ return 0;
+}
+
+int my_rw_destroy(my_rw_lock_t* rwp)
+{
+ DBUG_ASSERT(!rwp->have_exclusive_srwlock);
+ return 0;
+}
+
+#else
+
+/*
+ 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.
+*
+*
+* 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)
+{
+ 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
+
+ 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)
+ 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)
+ 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);
+}
+
+#endif /* !defined _WIN32 */
+#endif /* NEED_MY_RW_LOCK*/
+
+
+int rw_pr_init(rw_pr_lock_t *rwlock)
+{
+ pthread_mutex_init(&rwlock->lock, NULL);
+ pthread_cond_init(&rwlock->no_active_readers, NULL);
+ rwlock->active_readers= 0;
+ rwlock->writers_waiting_readers= 0;
+ rwlock->active_writer= FALSE;
+#ifdef SAFE_MUTEX
+ rwlock->writer_thread= 0;
+#endif
+ return 0;
+}
+
+
+int rw_pr_destroy(rw_pr_lock_t *rwlock)
+{
+ pthread_cond_destroy(&rwlock->no_active_readers);
+ pthread_mutex_destroy(&rwlock->lock);
+ return 0;
+}
+
+
+int rw_pr_rdlock(rw_pr_lock_t *rwlock)
+{
+ pthread_mutex_lock(&rwlock->lock);
+ /*
+ The fact that we were able to acquire 'lock' mutex means
+ that there are no active writers and we can acquire rd-lock.
+ Increment active readers counter to prevent requests for
+ wr-lock from succeeding and unlock mutex.
+ */
+ rwlock->active_readers++;
+ pthread_mutex_unlock(&rwlock->lock);
+ return 0;
+}
+
+
+int rw_pr_wrlock(rw_pr_lock_t *rwlock)
+{
+ pthread_mutex_lock(&rwlock->lock);
+
+ if (rwlock->active_readers != 0)
+ {
+ /* There are active readers. We have to wait until they are gone. */
+ rwlock->writers_waiting_readers++;
+
+ while (rwlock->active_readers != 0)
+ pthread_cond_wait(&rwlock->no_active_readers, &rwlock->lock);
+
+ rwlock->writers_waiting_readers--;
+ }
+
+ /*
+ We own 'lock' mutex so there is no active writers.
+ Also there are no active readers.
+ This means that we can grant wr-lock.
+ Not releasing 'lock' mutex until unlock will block
+ both requests for rd and wr-locks.
+ Set 'active_writer' flag to simplify unlock.
+
+ Thanks to the fact wr-lock/unlock in the absence of
+ contention from readers is essentially mutex lock/unlock
+ with a few simple checks make this rwlock implementation
+ wr-lock optimized.
+ */
+ rwlock->active_writer= TRUE;
+#ifdef SAFE_MUTEX
+ rwlock->writer_thread= pthread_self();
+#endif
+ return 0;
+}
+
+
+int rw_pr_unlock(rw_pr_lock_t *rwlock)
+{
+ if (rwlock->active_writer)
+ {
+ /* We are unlocking wr-lock. */
+#ifdef SAFE_MUTEX
+ rwlock->writer_thread= 0;
+#endif
+ rwlock->active_writer= FALSE;
+ if (rwlock->writers_waiting_readers)
+ {
+ /*
+ Avoid expensive cond signal in case when there is no contention
+ or it is wr-only.
+
+ Note that from view point of performance it would be better to
+ signal on the condition variable after unlocking mutex (as it
+ reduces number of contex switches).
+
+ Unfortunately this would mean that such rwlock can't be safely
+ used by MDL subsystem, which relies on the fact that it is OK
+ to destroy rwlock once it is in unlocked state.
+ */
+ pthread_cond_signal(&rwlock->no_active_readers);
+ }
+ pthread_mutex_unlock(&rwlock->lock);
+ }
+ else
+ {
+ /* We are unlocking rd-lock. */
+ pthread_mutex_lock(&rwlock->lock);
+ rwlock->active_readers--;
+ if (rwlock->active_readers == 0 &&
+ rwlock->writers_waiting_readers)
+ {
+ /*
+ If we are last reader and there are waiting
+ writers wake them up.
+ */
+ pthread_cond_signal(&rwlock->no_active_readers);
+ }
+ pthread_mutex_unlock(&rwlock->lock);
+ }
+ return 0;
+}
+
+
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