SemaphoreLockStrategy.php

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<?php
namespace TYPO3\CMS\Core\Locking;

/*
 * This file is part of the TYPO3 CMS project.
 *
 * It is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License, either version 2
 * of the License, or any later version.
 *
 * For the full copyright and license information, please read the
 * LICENSE.txt file that was distributed with this source code.
 *
 * The TYPO3 project - inspiring people to share!
 */

use TYPO3\CMS\Core\Locking\Exception\LockAcquireException;
use TYPO3\CMS\Core\Locking\Exception\LockCreateException;
use TYPO3\CMS\Core\Utility\GeneralUtility;

class SemaphoreLockStrategy implements LockingStrategyInterface
{
    const FILE_LOCK_FOLDER = 'typo3temp/var/locks/';

    protected $id;

    protected $resource;

    protected $filePath = '';

    protected $isAcquired = false;

    public function __construct($subject)
    {
        $path = PATH_site . self::FILE_LOCK_FOLDER;
        if (!is_dir($path)) {
            // Not using mkdir_deep on purpose here, if typo3temp/var itself
            // does not exist, this issue should be solved on a different
            // level of the application.
            if (!GeneralUtility::mkdir($path)) {
                throw new LockCreateException('Cannot create directory ' . $path, 1460976250);
            }
        }
        if (!is_writable($path)) {
            throw new LockCreateException('Cannot write to directory ' . $path, 1460976320);
        }
        $this->filePath = $path . 'sem_' . md5((string)$subject);
        touch($this->filePath);
        $this->id = ftok($this->filePath, 'A');
        if ($this->id === false) {
            throw new LockCreateException('Cannot create key for semaphore using path ' . $this->filePath, 1396278734);
        }
    }

    public function __destruct()
    {
        $this->release();
        // We do not call sem_remove() since this would remove the resource for other processes,
        // we leave that to the system. This is not clean, but there's no other way to determine when
        // a semaphore is no longer needed as a website is generally running endlessly
        // and we have no way to detect if there is a process currently waiting on that lock
        // or if the server is shutdown
    }

    public function release()
    {
        if (!$this->isAcquired) {
            return true;
        }
        $this->isAcquired = false;
        return (bool)@sem_release($this->resource);
    }

    public function isAcquired()
    {
        return $this->isAcquired;
    }

    public static function getCapabilities()
    {
        if (function_exists('sem_get')) {
            return self::LOCK_CAPABILITY_EXCLUSIVE;
        }
        return 0;
    }

    public function acquire($mode = self::LOCK_CAPABILITY_EXCLUSIVE)
    {
        if ($this->isAcquired) {
            return true;
        }

        $this->resource = sem_get($this->id, 1);
        if ($this->resource === false) {
            throw new LockAcquireException('Unable to get semaphore with id ' . $this->id, 1313828196);
        }

        $this->isAcquired = (bool)sem_acquire($this->resource);
        return $this->isAcquired;
    }

    public static function getPriority()
    {
        return 25;
    }

    public function destroy()
    {
        if ($this->resource) {
            sem_remove($this->resource);
            @unlink($this->filePath);
        }
    }
}