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/* Copyright 2000-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/*Read/Write locking implementation based on the MultiLock code from
* Stephen Beaulieu <hippo@be.com>
*/
#include "apr_arch_thread_rwlock.h"
#include "apr_strings.h"
#include "apr_portable.h"
#define BIG_NUM 100000
static apr_status_t _thread_rw_cleanup(void * data)
{
apr_thread_rwlock_t *mutex = (apr_thread_rwlock_t*)data;
if (mutex->ReadCount != 0) {
while (atomic_add(&mutex->ReadCount , -1) > 1){
release_sem (mutex->Read);
}
}
if (mutex->WriteCount != 0) {
while (atomic_add(&mutex->WriteCount , -1) > 1){
release_sem (mutex->Write);
}
}
if (mutex->LockCount != 0) {
while (atomic_add(&mutex->LockCount , -1) > 1){
release_sem (mutex->Lock);
}
}
delete_sem(mutex->Read);
delete_sem(mutex->Write);
delete_sem(mutex->Lock);
return APR_SUCCESS;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_create(apr_thread_rwlock_t **rwlock,
apr_pool_t *pool)
{
apr_thread_rwlock_t *new;
new = (apr_thread_rwlock_t *)apr_pcalloc(pool, sizeof(apr_thread_rwlock_t));
if (new == NULL){
return APR_ENOMEM;
}
new->pool = pool;
/* we need to make 3 locks... */
new->ReadCount = 0;
new->WriteCount = 0;
new->LockCount = 0;
new->Read = create_sem(0, "APR_ReadLock");
new->Write = create_sem(0, "APR_WriteLock");
new->Lock = create_sem(0, "APR_Lock");
if (new->Lock < 0 || new->Read < 0 || new->Write < 0) {
_thread_rw_cleanup(new);
return -1;
}
apr_pool_cleanup_register(new->pool, (void *)new, _thread_rw_cleanup,
apr_pool_cleanup_null);
(*rwlock) = new;
return APR_SUCCESS;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_rdlock(apr_thread_rwlock_t *rwlock)
{
int32 rv = APR_SUCCESS;
if (find_thread(NULL) == rwlock->writer) {
/* we're the writer - no problem */
rwlock->Nested++;
} else {
/* we're not the writer */
int32 r = atomic_add(&rwlock->ReadCount, 1);
if (r < 0) {
/* Oh dear, writer holds lock, wait for sem */
rv = acquire_sem_etc(rwlock->Read, 1, B_DO_NOT_RESCHEDULE,
B_INFINITE_TIMEOUT);
}
}
return rv;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock)
{
return APR_ENOTIMPL;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_wrlock(apr_thread_rwlock_t *rwlock)
{
int rv = APR_SUCCESS;
if (find_thread(NULL) == rwlock->writer) {
rwlock->Nested++;
} else {
/* we're not the writer... */
if (atomic_add(&rwlock->LockCount, 1) >= 1) {
/* we're locked - acquire the sem */
rv = acquire_sem_etc(rwlock->Lock, 1, B_DO_NOT_RESCHEDULE,
B_INFINITE_TIMEOUT);
}
if (rv == APR_SUCCESS) {
/* decrement the ReadCount to a large -ve number so that
* we block on new readers...
*/
int32 readers = atomic_add(&rwlock->ReadCount, -BIG_NUM);
if (readers > 0) {
/* readers are holding the lock */
rv = acquire_sem_etc(rwlock->Write, readers, B_DO_NOT_RESCHEDULE,
B_INFINITE_TIMEOUT);
}
if (rv == APR_SUCCESS)
rwlock->writer = find_thread(NULL);
}
}
return rv;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock)
{
return APR_ENOTIMPL;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_unlock(apr_thread_rwlock_t *rwlock)
{
apr_status_t rv = APR_SUCCESS;
int32 readers;
/* we know we hold the lock, so don't check it :) */
if (find_thread(NULL) == rwlock->writer) {
/* we know we hold the lock, so don't check it :) */
if (rwlock->Nested > 1) {
/* we're recursively locked */
rwlock->Nested--;
return APR_SUCCESS;
}
/* OK so we need to release the sem if we have it :) */
readers = atomic_add(&rwlock->ReadCount, BIG_NUM) + BIG_NUM;
if (readers > 0) {
rv = release_sem_etc(rwlock->Read, readers, B_DO_NOT_RESCHEDULE);
}
if (rv == APR_SUCCESS) {
rwlock->writer = -1;
if (atomic_add(&rwlock->LockCount, -1) > 1) {
rv = release_sem_etc(rwlock->Lock, 1, B_DO_NOT_RESCHEDULE);
}
}
} else {
/* We weren't the Writer, so just release the ReadCount... */
if (atomic_add(&rwlock->ReadCount, -1) < 0) {
/* we have a writer waiting for the lock, so release it */
rv = release_sem_etc(rwlock->Write, 1, B_DO_NOT_RESCHEDULE);
}
}
return rv;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_destroy(apr_thread_rwlock_t *rwlock)
{
apr_status_t stat;
if ((stat = _thread_rw_cleanup(rwlock)) == APR_SUCCESS) {
apr_pool_cleanup_kill(rwlock->pool, rwlock, _thread_rw_cleanup);
return APR_SUCCESS;
}
return stat;
}
APR_POOL_IMPLEMENT_ACCESSOR(thread_rwlock)
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