FileLockStrategy.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\LockAcquireWouldBlockException;
use TYPO3\CMS\Core\Locking\Exception\LockCreateException;
use TYPO3\CMS\Core\Utility\GeneralUtility;

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

    protected $filePointer;

    protected $filePath;

    protected $isAcquired = false;

    public function __construct($subject)
    {
        /*
         * Tests if the directory for simple locks is available.
         * If not, the directory will be created. The lock path is usually
         * below typo3temp, typo3temp itself should exist already
         */
        $path = PATH_site . self::FILE_LOCK_FOLDER;
        if (!is_dir($path)) {
            // Not using mkdir_deep on purpose here, if typo3temp 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 ' . $path, 1395140007);
            }
        }
        if (!is_writable($path)) {
            throw new LockCreateException('Cannot write to directory ' . $path, 1396278700);
        }
        $this->filePath = $path . 'flock_' . md5((string)$subject);
    }

    public function __destruct()
    {
        $this->release();
    }

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

        $this->filePointer = fopen($this->filePath, 'c');
        if ($this->filePointer === false) {
            throw new LockAcquireException('Lock file could not be opened', 1294586099);
        }
        GeneralUtility::fixPermissions($this->filePath);

        $operation = $mode & self::LOCK_CAPABILITY_EXCLUSIVE ? LOCK_EX : LOCK_SH;
        if ($mode & self::LOCK_CAPABILITY_NOBLOCK) {
            $operation |= LOCK_NB;
        }

        $wouldBlock = 0;
        $this->isAcquired = flock($this->filePointer, $operation, $wouldBlock);

        if ($mode & self::LOCK_CAPABILITY_NOBLOCK && !$this->isAcquired && $wouldBlock) {
            throw new LockAcquireWouldBlockException('Failed to acquire lock because the request would block.', 1428700748);
        }

        return $this->isAcquired;
    }

    public function release()
    {
        if (!$this->isAcquired) {
            return true;
        }
        $success = true;
        if (is_resource($this->filePointer)) {
            if (flock($this->filePointer, LOCK_UN) === false) {
                $success = false;
            }
            fclose($this->filePointer);
        }
        $this->isAcquired = false;
        return $success;
    }

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

    public static function getPriority()
    {
        return 75;
    }

    public static function getCapabilities()
    {
        if (PHP_SAPI === 'isapi') {
            // From php docs: When using a multi-threaded server API like ISAPI you may not be able to rely on flock()
            // to protect files against other PHP scripts running in parallel threads of the same server instance!
            return 0;
        }
        $capabilities = self::LOCK_CAPABILITY_EXCLUSIVE | self::LOCK_CAPABILITY_SHARED;
        if (TYPO3_OS !== 'WIN'
            || version_compare(PHP_VERSION, '5.5.22', '>') && version_compare(PHP_VERSION, '5.6.0', '<')
            || version_compare(PHP_VERSION, '5.6.6', '>')
        ) {
            $capabilities |= self::LOCK_CAPABILITY_NOBLOCK;
        }

        return $capabilities;
    }

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