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/* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
#include "apr.h"
#include "apr_private.h"
#include "apr_general.h"
#include "apr_strings.h"
#include "apr_arch_thread_rwlock.h"
#include "apr_portable.h"
static apr_status_t thread_rwlock_cleanup(void *data)
{
apr_thread_rwlock_t *rwlock = data;
if (! CloseHandle(rwlock->read_event))
return apr_get_os_error();
if (! CloseHandle(rwlock->write_mutex))
return apr_get_os_error();
return APR_SUCCESS;
}
APR_DECLARE(apr_status_t)apr_thread_rwlock_create(apr_thread_rwlock_t **rwlock,
apr_pool_t *pool)
{
*rwlock = apr_palloc(pool, sizeof(**rwlock));
(*rwlock)->pool = pool;
(*rwlock)->readers = 0;
if (! ((*rwlock)->read_event = CreateEvent(NULL, TRUE, FALSE, NULL))) {
*rwlock = NULL;
return apr_get_os_error();
}
if (! ((*rwlock)->write_mutex = CreateMutex(NULL, FALSE, NULL))) {
CloseHandle((*rwlock)->read_event);
*rwlock = NULL;
return apr_get_os_error();
}
apr_pool_cleanup_register(pool, *rwlock, thread_rwlock_cleanup,
apr_pool_cleanup_null);
return APR_SUCCESS;
}
static apr_status_t apr_thread_rwlock_rdlock_core(apr_thread_rwlock_t *rwlock,
DWORD milliseconds)
{
DWORD code = WaitForSingleObject(rwlock->write_mutex, milliseconds);
if (code == WAIT_FAILED || code == WAIT_TIMEOUT)
return APR_FROM_OS_ERROR(code);
/* We've successfully acquired the writer mutex, we can't be locked
* for write, so it's OK to add the reader lock. The writer mutex
* doubles as race condition protection for the readers counter.
*/
InterlockedIncrement(&rwlock->readers);
if (! ResetEvent(rwlock->read_event))
return apr_get_os_error();
if (! ReleaseMutex(rwlock->write_mutex))
return apr_get_os_error();
return APR_SUCCESS;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_rdlock(apr_thread_rwlock_t *rwlock)
{
return apr_thread_rwlock_rdlock_core(rwlock, INFINITE);
}
APR_DECLARE(apr_status_t)
apr_thread_rwlock_tryrdlock(apr_thread_rwlock_t *rwlock)
{
return apr_thread_rwlock_rdlock_core(rwlock, 0);
}
static apr_status_t
apr_thread_rwlock_wrlock_core(apr_thread_rwlock_t *rwlock, DWORD milliseconds)
{
DWORD code = WaitForSingleObject(rwlock->write_mutex, milliseconds);
if (code == WAIT_FAILED || code == WAIT_TIMEOUT)
return APR_FROM_OS_ERROR(code);
/* We've got the writer lock but we have to wait for all readers to
* unlock before it's ok to use it.
*/
if (rwlock->readers) {
/* Must wait for readers to finish before returning, unless this
* is an trywrlock (milliseconds == 0):
*/
code = milliseconds
? WaitForSingleObject(rwlock->read_event, milliseconds)
: WAIT_TIMEOUT;
if (code == WAIT_FAILED || code == WAIT_TIMEOUT) {
/* Unable to wait for readers to finish, release write lock: */
if (! ReleaseMutex(rwlock->write_mutex))
return apr_get_os_error();
return APR_FROM_OS_ERROR(code);
}
}
return APR_SUCCESS;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_wrlock(apr_thread_rwlock_t *rwlock)
{
return apr_thread_rwlock_wrlock_core(rwlock, INFINITE);
}
APR_DECLARE(apr_status_t)apr_thread_rwlock_trywrlock(apr_thread_rwlock_t *rwlock)
{
return apr_thread_rwlock_wrlock_core(rwlock, 0);
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_unlock(apr_thread_rwlock_t *rwlock)
{
apr_status_t rv = 0;
/* First, guess that we're unlocking a writer */
if (! ReleaseMutex(rwlock->write_mutex))
rv = apr_get_os_error();
if (rv == APR_FROM_OS_ERROR(ERROR_NOT_OWNER)) {
/* Nope, we must have a read lock */
if (rwlock->readers &&
! InterlockedDecrement(&rwlock->readers) &&
! SetEvent(rwlock->read_event)) {
rv = apr_get_os_error();
}
else {
rv = 0;
}
}
return rv;
}
APR_DECLARE(apr_status_t) apr_thread_rwlock_destroy(apr_thread_rwlock_t *rwlock)
{
return apr_pool_cleanup_run(rwlock->pool, rwlock, thread_rwlock_cleanup);
}
APR_POOL_IMPLEMENT_ACCESSOR(thread_rwlock)
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