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/** BEGIN COPYRIGHT BLOCK
* 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.
*
* In addition, as a special exception, Red Hat, Inc. gives You the additional
* right to link the code of this Program with code not covered under the GNU
* General Public License ("Non-GPL Code") and to distribute linked combinations
* including the two, subject to the limitations in this paragraph. Non-GPL Code
* permitted under this exception must only link to the code of this Program
* through those well defined interfaces identified in the file named EXCEPTION
* found in the source code files (the "Approved Interfaces"). The files of
* Non-GPL Code may instantiate templates or use macros or inline functions from
* the Approved Interfaces without causing the resulting work to be covered by
* the GNU General Public License. Only Red Hat, Inc. may make changes or
* additions to the list of Approved Interfaces. You must obey the GNU General
* Public License in all respects for all of the Program code and other code used
* in conjunction with the Program except the Non-GPL Code covered by this
* exception. If you modify this file, you may extend this exception to your
* version of the file, but you are not obligated to do so. If you do not wish to
* provide this exception without modification, you must delete this exception
* statement from your version and license this file solely under the GPL without
* exception.
*
*
* Copyright (C) 2001 Sun Microsystems, Inc. Used by permission.
* Copyright (C) 2005 Red Hat, Inc.
* All rights reserved.
* END COPYRIGHT BLOCK **/
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
/*
* rwlock.c - generic multiple reader, single-writer locking routines.
*
* The general idea is:
*
* If you have a data structure which you'd like to allow multiple threads
* to read, but only one thread at a time to write, you include in your
* data structure a pointer to an rwl structure, and call rwl_new() to
* obtain an allocated and initialized rwl structure.
*
* Then, call the appropriate functions via the provided function pointers
* to acquire/relinquish read or write locks on your data structure. You
* may want to provide some convenience macros to make the code prettier.
*
* The semantics are:
* - a thread attempting to obtain a read lock will succeed immediately as
* long as there are no threads with write locks.
* - a thread attempting to obtain a write lock will wait until all readers
* have relinquished their read locks.
* - a thread attempting to obtain a write lock blocks other threads from
* obtaining read locks. As long as all readers release their locks,
* the write will eventually get the lock.
*/
#include "slap.h"
#include <prlock.h>
#include <prcvar.h>
#include "rwlock.h"
/*
* Function: __rwl_acquire_read_lock
*
* Description: acquire a read lock.
*
* Arguments: rp: pointer to an rwl stucture
*
* Returns: 0 on success, -1 on failure.
*/
static int
__rwl_acquire_read_lock( rwl *rp )
{
if ( rp == NULL ) {
return -1;
}
PR_Lock( rp->rwl_writers_mutex );
PR_Lock( rp->rwl_readers_mutex );
rp->rwl_num_readers++;
(void)PR_Unlock( rp->rwl_readers_mutex );
(void)PR_Unlock( rp->rwl_writers_mutex );
return 0;
}
/*
* Function: __rwl_acquire_write_lock
*
* Description: acquire a write lock.
*
* Arguments: rp: pointer to an rwl stucture
*
* Returns: 0 on success, -1 on failure.
*/
static int
__rwl_acquire_write_lock( rwl *rp )
{
if ( rp == NULL ) {
return -1;
}
PR_Lock( rp->rwl_writers_mutex );
PR_Lock( rp->rwl_readers_mutex );
rp->rwl_writer_waiting = 1;
while ( rp->rwl_num_readers > 0 ) {
if ( PR_WaitCondVar( rp->rwl_writer_waiting_cv, PR_INTERVAL_NO_TIMEOUT ) != 0 ) {
(void)PR_Unlock( rp->rwl_writers_mutex );
(void)PR_Unlock( rp->rwl_readers_mutex );
return -1;
}
}
/* XXXggood should rwl_writer_waiting be set zero here? */
return 0;
}
/*
* Function: __rwl_relinquish_read_lock
*
* Description: relinquish a read lock.
*
* Arguments: rp: pointer to an rwl stucture
*
* Returns: 0 on success, -1 on failure.
*/
static int
__rwl_relinquish_read_lock( rwl *rp )
{
if ( rp == NULL ) {
return -1;
}
PR_Lock( rp->rwl_readers_mutex );
if ( --rp->rwl_num_readers == 0 && rp->rwl_writer_waiting ) {
PR_NotifyCondVar( rp->rwl_writer_waiting_cv );
}
(void)PR_Unlock( rp->rwl_readers_mutex );
return 0;
}
/*
* Function: __rwl_relinquish_write_lock
*
* Description: relinquish a write lock.
*
* Arguments: rp: pointer to an rwl stucture
*
* Returns: 0 on success, -1 on failure.
*/
static int
__rwl_relinquish_write_lock( rwl *rp )
{
if ( rp == NULL ) {
return -1;
}
rp->rwl_writer_waiting = 0;
(void)PR_Unlock( rp->rwl_readers_mutex );
(void)PR_Unlock( rp->rwl_writers_mutex );
return 0;
}
/*
* Function: rwl_new
*
* Description: allocate and initialize a wrl structure.
*
* Arguments: none
*
* Returns: on success, returns a pointer to an allocated, initialized rwl structure.
* on failure, returns NULL.
*
*/
rwl *
rwl_new()
{
rwl *rp;
rp = (rwl *)slapi_ch_malloc( sizeof( rwl ));
if (( rp->rwl_readers_mutex = PR_NewLock()) == NULL ) {
slapi_ch_free( (void **)&rp );
return NULL;
}
if (( rp->rwl_writers_mutex = PR_NewLock()) == NULL ) {
PR_DestroyLock( rp->rwl_readers_mutex );
slapi_ch_free( (void **)&rp );
return NULL;
}
if (( rp->rwl_writer_waiting_cv = PR_NewCondVar( rp->rwl_readers_mutex )) == NULL ) {
PR_DestroyLock( rp->rwl_readers_mutex );
PR_DestroyLock( rp->rwl_writers_mutex );
slapi_ch_free( (void **)&rp );
}
rp->rwl_num_readers = rp->rwl_writer_waiting = 0;
rp->rwl_acquire_read_lock = __rwl_acquire_read_lock;
rp->rwl_relinquish_read_lock = __rwl_relinquish_read_lock;
rp->rwl_acquire_write_lock = __rwl_acquire_write_lock;
rp->rwl_relinquish_write_lock = __rwl_relinquish_write_lock;
return rp;
}
/*
* Function: rwl_free
*
* Description: deallocates and frees an rwl structure.
*
* Arguments: rh: handle to an rwl structure.
*
* Returns: nothing
*/
void
rwl_free( rwl **rh )
{
rwl *rp;
if ( rh == NULL || *rh == NULL ) {
return;
}
rp = *rh;
if ( rp->rwl_readers_mutex != NULL ) {
PR_DestroyLock( rp->rwl_readers_mutex );
}
if ( rp->rwl_writers_mutex != NULL ) {
PR_DestroyLock( rp->rwl_writers_mutex );
}
if ( rp->rwl_writer_waiting_cv != NULL ) {
PR_DestroyCondVar( rp->rwl_writer_waiting_cv );
}
memset( rp, '\0', sizeof( rwl ));
slapi_ch_free( (void **)&rp );
*rh = NULL;
}
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