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<?php
/**
* Copyright 2017 Google Inc.
*
* 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.
*/
namespace Google\Cloud\Core\Lock;
use Google\Cloud\Core\SysvTrait;
/**
* Semaphore based lock implementation.
*
* @see http://php.net/manual/en/book.sem.php
* @experimental The experimental flag means that while we believe this method
* or class is ready for use, it may change before release in backwards-
* incompatible ways. Please use with caution, and test thoroughly when
* upgrading.
*/
class SemaphoreLock implements LockInterface
{
use LockTrait;
use SysvTrait;
/**
* @var int
*/
private $key;
/**
* @var resource|null
*/
private $semaphoreId;
/**
* @param int $key A key.
* @throws \InvalidArgumentException If an invalid key is provided.
* @throws \RuntimeException If the System V IPC extensions are missing.
*/
public function __construct($key)
{
if (!$this->isSysvIPCLoaded()) {
throw new \RuntimeException('SystemV IPC extensions are required.');
}
if (!is_int($key)) {
throw new \InvalidArgumentException('The provided key must be an integer.');
}
$this->key = $key;
}
/**
* Acquires a lock that will block until released.
*
* @param array $options [optional] {
* Configuration options.
*
* @type bool $blocking Whether the process should block while waiting
* to acquire the lock. **Defaults to** true.
* }
* @return bool
* @throws \RuntimeException If the lock fails to be acquired.
*/
public function acquire(array $options = [])
{
$options += [
'blocking' => true
];
if ($this->semaphoreId) {
return true;
}
$this->semaphoreId = $this->initializeId();
if (!sem_acquire($this->semaphoreId, !$options['blocking'])) {
$this->semaphoreId = null;
throw new \RuntimeException('Failed to acquire lock.');
}
return true;
}
/**
* Releases the lock.
*
* @throws \RuntimeException If the lock fails to release.
*/
public function release()
{
if ($this->semaphoreId) {
$released = sem_release($this->semaphoreId);
$this->semaphoreId = null;
if (!$released) {
throw new \RuntimeException('Failed to release lock.');
}
}
}
/**
* Initializes the semaphore ID.
*
* @return resource
* @throws \RuntimeException If semaphore ID fails to generate.
*/
private function initializeId()
{
$semaphoreId = sem_get($this->key);
if (!$semaphoreId) {
throw new \RuntimeException('Failed to generate semaphore ID.');
}
return $semaphoreId;
}
}
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