SemaphoreLockStrategy.php

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<?php
 
/*
 * 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!
 */
 
namespace ‪TYPO3\CMS\Core\Locking;
 
use ‪TYPO3\CMS\Core\Core\Environment;
use ‪TYPO3\CMS\Core\Locking\Exception\LockAcquireException;
use ‪TYPO3\CMS\Core\Locking\Exception\LockCreateException;
use ‪TYPO3\CMS\Core\Security\BlockSerializationTrait;
use ‪TYPO3\CMS\Core\Utility\GeneralUtility;
 
class ‪SemaphoreLockStrategy implements ‪LockingStrategyInterface
{
    use ‪BlockSerializationTrait;
 
    const ‪FILE_LOCK_FOLDER = 'lock/';
    const ‪DEFAULT_PRIORITY = 25;
 
    protected ‪$id;
 
    protected ‪$resource;
 
    protected ‪$filePath = '';
 
    protected ‪$isAcquired = false;
 
    public function ‪__construct($subject)
    {
        /*
         * Tests if the directory for semaphore locks is available.
         * If not, the directory will be created. The lock path is usually
         * below typo3temp/var, typo3temp/var itself should exist already (or root-path/var/ respectively)
         */
        if (‪$GLOBALS['TYPO3_CONF_VARS']['SYS']['locking']['strategies'][self::class]['lockFileDir'] ?? false) {
            $path = ‪Environment::getProjectPath() . '/'
                    . trim(‪$GLOBALS['TYPO3_CONF_VARS']['SYS']['locking']['strategies'][self::class]['lockFileDir'], ' /')
                    . '/';
        } else {
            $path = ‪Environment::getVarPath() . '/' . ‪self::FILE_LOCK_FOLDER;
        }
        if (!is_dir($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 ‪$GLOBALS['TYPO3_CONF_VARS']['SYS']['locking']['strategies'][self::class]['priority']
            ?? ‪self::DEFAULT_PRIORITY;
    }
 
    public function ‪destroy()
    {
        if ($this->resource) {
            sem_remove($this->resource);
            @unlink($this->filePath);
        }
    }
}