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/*
* thread_rwlock.c
*
* $Id$
*
* Read-write locks implementation
*
* This file is part of the OpenLink Software Virtuoso Open-Source (VOS)
* project.
*
* Copyright (C) 1998-2012 OpenLink Software
*
* This project 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; only version 2 of the License, dated June 1991.
*
* 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 02110-1301 USA
*
*
*/
#include "thread_int.h"
struct rwlock_s {
dk_mutex_t *mtx;
semaphore_t *read_sem;
semaphore_t *write_sem;
int state; /* 0 = idle >0 = # of readers -1 = writer */
int blocked_writers;
int blocked_readers;
};
rwlock_t *
rwlock_allocate (void)
{
NEW_VARZ (rwlock_t, l);
l->mtx = mutex_allocate ();
l->read_sem = semaphore_allocate (0);
l->write_sem = semaphore_allocate (0);
l->state = 0;
l->blocked_writers = 0;
l->blocked_readers = 0;
return l;
}
void
rwlock_free (rwlock_t *l)
{
mutex_free (l->mtx);
semaphore_free (l->read_sem);
semaphore_free (l->write_sem);
dk_free (l, sizeof (*l));
}
void
rwlock_rdlock (rwlock_t *l)
{
mutex_enter (l->mtx);
while (l->blocked_writers || l->state < 0)
{
++l->blocked_readers;
mutex_leave (l->mtx);
semaphore_enter (l->read_sem);
mutex_enter (l->mtx);
--l->blocked_readers;
}
++l->state;
mutex_leave (l->mtx);
}
int
rwlock_tryrdlock (rwlock_t *l)
{
mutex_enter (l->mtx);
if (l->blocked_writers || l->state < 0)
{
mutex_leave (l->mtx);
return 0;
}
++l->state;
mutex_leave (l->mtx);
return 1;
}
void
rwlock_wrlock (rwlock_t *l)
{
mutex_enter (l->mtx);
while (l->state)
{
++l->blocked_writers;
mutex_leave (l->mtx);
semaphore_enter (l->write_sem);
mutex_enter (l->mtx);
--l->blocked_writers;
}
l->state = -1;
mutex_leave (l->mtx);
}
int
rwlock_trywrlock (rwlock_t *l)
{
mutex_enter (l->mtx);
if (l->state)
{
mutex_leave (l->mtx);
return 0;
}
l->state = -1;
mutex_leave (l->mtx);
return 1;
}
void
rwlock_unlock (rwlock_t *l)
{
mutex_enter (l->mtx);
if (l->state > 0)
{
if (--l->state == 0 && l->blocked_writers)
semaphore_leave (l->write_sem);
}
else if (l->state < 0)
{
l->state = 0;
if (l->blocked_writers)
{
/*
* wake up a waiting writer
*/
semaphore_leave (l->write_sem);
}
else
{
/*
* wake up all the waiting readers
*/
int i;
for (i = 0; i < l->blocked_readers; i++)
semaphore_leave (l->read_sem);
}
}
mutex_leave (l->mtx);
}
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