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File: class.t3lib_lock.php
<?php
/***************************************************************
 *  Copyright notice
 *
 *  (c) 2008-2011 Michael Stucki (michael@typo3.org)
 *  All rights reserved
 *
 *  This script is part of the TYPO3 project. The TYPO3 project is
 *  free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  The GNU General Public License can be found at
 *  http://www.gnu.org/copyleft/gpl.html.
 *  A copy is found in the textfile GPL.txt and important notices to the license
 *  from the author is found in LICENSE.txt distributed with these scripts.
 *
 *
 *  This script is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  This copyright notice MUST APPEAR in all copies of the script!
 ***************************************************************/
/**
 * Class for providing locking features in TYPO3
 *
 * $Id$
 *
 * @author	Michael Stucki <michael@typo3.org>
 */


/**
 * TYPO3 locking class
 * This class provides an abstract layer to various locking features for TYPO3
 *
 * It is intended to blocks requests until some data has been generated.
 * This is especially useful if two clients are requesting the same website short after each other. While the request of client 1 triggers building and caching of the website, client 2 will be waiting at this lock.
 *
 * @author	Michael Stucki <michael@typo3.org>
 * @package TYPO3
 * @subpackage t3lib
 * @see	class.t3lib_tstemplate.php, class.tslib_fe.php
 */
class t3lib_lock {
	protected $method;
	protected $id; // Identifier used for this lock
	protected $resource; // Resource used for this lock (can be a file or a semaphore resource)
	protected $filepointer;
	protected $isAcquired = FALSE;

	protected $loops = 150; // Number of times a locked resource is tried to be acquired. This is only used by manual locks like the "simple" method.
	protected $step = 200; // Milliseconds after lock acquire is retried. $loops * $step results in the maximum delay of a lock. Only used by manual locks like the "simple" method.
	protected $syslogFacility = 'cms';
	protected $isLoggingEnabled = TRUE;


	/**
	 * Constructor:
	 * initializes locking, check input parameters and set variables accordingly.
	 *
	 * @param	string		ID to identify this lock in the system
	 * @param	string		Define which locking method to use. Defaults to "simple".
	 * @param	integer		Number of times a locked resource is tried to be acquired. This is only used by manual locks like the "simple" method.
	 * @param	integer		Milliseconds after lock acquire is retried. $loops * $step results in the maximum delay of a lock. Only used by manual locks like the "simple" method.
	 * @return	boolean		Returns true unless something went wrong
	 */
	public function __construct($id, $method = '', $loops = 0, $step = 0) {

			// Input checks
		$id = (string) $id; // Force ID to be string
		if (intval($loops)) {
			$this->loops = intval($loops);
		}
		if (intval($step)) {
			$this->step = intval($step);
		}

			// Detect locking method
		if (in_array($method, array('disable', 'simple', 'flock', 'semaphore'))) {
			$this->method = $method;
		} else {
			throw new Exception('No such method "' . $method . '"');
		}

		$success = FALSE;
		switch ($this->method) {
			case 'simple':
			case 'flock':
				$path = PATH_site . 'typo3temp/locks/';
				if (!is_dir($path)) {
					t3lib_div::mkdir($path);
				}
				$this->id = md5($id);
				$this->resource = $path . $this->id;
				$success = TRUE;
			break;
			case 'semaphore':
				$this->id = abs(crc32($id));
				if (($this->resource = sem_get($this->id, 1)) == TRUE) {
					$success = TRUE;
				}
			break;
			case 'disable':
				return FALSE;
			break;
		}

		return $success;
	}

	/**
	 * Destructor:
	 * Releases lock automatically when instance is destroyed.
	 *
	 * @return	void
	 */
	function __destruct() {
		$this->release();
	}

	/**
	 * Acquire a lock and return when successful. If the lock is already open, the client will be
	 *
	 * It is important to know that the lock will be acquired in any case, even if the request was blocked first. Therefore, the lock needs to be released in every situation.
	 *
	 * @return	boolean		Returns true if lock could be acquired without waiting, false otherwise.
	 */
	public function acquire() {
		$noWait = TRUE; // Default is TRUE, which means continue without caring for other clients. In the case of TYPO3s cache management, this has no negative effect except some resource overhead.
		$isAcquired = TRUE;

		switch ($this->method) {
			case 'simple':
				if (is_file($this->resource)) {
					$this->sysLog('Waiting for a different process to release the lock');
					$maxExecutionTime = ini_get('max_execution_time');
					$maxAge = time() - ($maxExecutionTime ? $maxExecutionTime : 120);
					if (@filectime($this->resource) < $maxAge) {
						@unlink($this->resource);
						$this->sysLog('Unlink stale lockfile');
					}
				}

				$isAcquired = FALSE;
				for ($i = 0; $i < $this->loops; $i++) {
					$filepointer = @fopen($this->resource, 'x');
					if ($filepointer !== FALSE) {
						fclose($filepointer);
						$this->sysLog('Lock aquired');
						$noWait = ($i === 0);
						$isAcquired = TRUE;
						break;
					}
					usleep($this->step * 1000);
				}

				if (!$isAcquired) {
					throw new Exception('Lock file could not be created');
				}

				t3lib_div::fixPermissions($this->resource);
			break;
			case 'flock':
				if (($this->filepointer = fopen($this->resource, 'w+')) == FALSE) {
					throw new Exception('Lock file could not be opened');
				}

				if (flock($this->filepointer, LOCK_EX | LOCK_NB) == TRUE) { // Lock without blocking
					$noWait = TRUE;
				} elseif (flock($this->filepointer, LOCK_EX) == TRUE) { // Lock with blocking (waiting for similar locks to become released)
					$noWait = FALSE;
				} else {
					throw new Exception('Could not lock file "' . $this->resource . '"');
				}
			break;
			case 'semaphore':
				if (sem_acquire($this->resource)) {
						// Unfortunately it seems not possible to find out if the request was blocked, so we return FALSE in any case to make sure the operation is tried again.
					$noWait = FALSE;
				}
			break;
			case 'disable':
				$noWait = FALSE;
				$isAcquired = FALSE;
			break;
		}

		$this->isAcquired = $isAcquired;
		return $noWait;
	}

	/**
	 * Release the lock
	 *
	 * @return	boolean		Returns TRUE on success or FALSE on failure
	 */
	public function release() {
		if (!$this->isAcquired) {
			return TRUE;
		}

		$success = TRUE;
		switch ($this->method) {
			case 'simple':
				if (t3lib_div::isAllowedAbsPath($this->resource) && t3lib_div::isFirstPartOfStr($this->resource, PATH_site . 'typo3temp/locks/')) {
					if (unlink($this->resource) == FALSE) {
						$success = FALSE;
					}
				}
			break;
			case 'flock':
				if (flock($this->filepointer, LOCK_UN) == FALSE) {
					$success = FALSE;
				}
				fclose($this->filepointer);
				if (t3lib_div::isAllowedAbsPath($this->resource) && t3lib_div::isFirstPartOfStr($this->resource, PATH_site . 'typo3temp/locks/')) {
					unlink($this->resource);
				}
			break;
			case 'semaphore':
				if (@sem_release($this->resource)) {
					sem_remove($this->resource);
				} else {
					$success = FALSE;
				}
			break;
			case 'disable':
				$success = FALSE;
			break;
		}

		$this->isAcquired = FALSE;
		return $success;
	}

	/**
	 * Return the locking method which is currently used
	 *
	 * @return	string		Locking method
	 */
	public function getMethod() {
		return $this->method;
	}

	/**
	 * Return the ID which is currently used
	 *
	 * @return	string		Locking ID
	 */
	public function getId() {
		return $this->id;
	}

	/**
	 * Return the resource which is currently used.
	 * Depending on the locking method this can be a filename or a semaphore resource.
	 *
	 * @return	mixed		Locking resource (filename as string or semaphore as resource)
	 */
	public function getResource() {
		return $this->resource;
	}

	/**
	 * Return the status of a lock
	 *
	 * @return	string		Returns TRUE if lock is acquired, FALSE otherwise
	 */
	public function getLockStatus() {
		return $this->isAcquired;
	}

	/**
	 * Sets the facility (extension name) for the syslog entry.
	 *
	 * @param string $syslogFacility
	 */
	public function setSyslogFacility($syslogFacility) {
		$this->syslogFacility = $syslogFacility;
	}

	/**
	 * Enable/ disable logging
	 *
	 * @param boolean $isLoggingEnabled
	 */
	public function setEnableLogging($isLoggingEnabled) {
		$this->isLoggingEnabled = $isLoggingEnabled;
	}

	/**
	 * Adds a common log entry for this locking API using t3lib_div::sysLog().
	 * Example: 25-02-08 17:58 - cms: Locking [simple::0aeafd2a67a6bb8b9543fb9ea25ecbe2]: Acquired
	 *
	 * @param	string		$message: The message to be logged
	 * @param	integer		$severity: Severity - 0 is info (default), 1 is notice, 2 is warning, 3 is error, 4 is fatal error
	 * @return	void
	 */
	public function sysLog($message, $severity = 0) {
		if ($this->isLoggingEnabled) {
			t3lib_div::sysLog('Locking [' . $this->method . '::' . $this->id . ']: ' . trim($message), $this->syslogFacility, $severity);
		}
	}
}


if (defined('TYPO3_MODE') && isset($GLOBALS['TYPO3_CONF_VARS'][TYPO3_MODE]['XCLASS']['t3lib/class.t3lib_lock.php'])) {
	include_once($GLOBALS['TYPO3_CONF_VARS'][TYPO3_MODE]['XCLASS']['t3lib/class.t3lib_lock.php']);
}
?>