class.t3lib_lock.php

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<?php
/***************************************************************
*  Copyright notice
*
*  (c) 2008 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: class.t3lib_lock.php 3510 2008-04-01 20:42:57Z flyguide $
 *
 * @author  Michael Stucki <michael@typo3.org>
 */

require_once(PATH_t3lib.'class.t3lib_div.php');














/**
 * 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.





    /**
     * 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, $steps=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');
                    $i = 0;
                    while ($i<$this->loops) {
                        $i++;
                        usleep($this->step*1000);
                        clearstatcache();
                        if (!is_file($this->resource)) {    // Lock became free, leave the loop
                            $this->sysLog('Different process released the lock');
                            $noWait = false;
                            break;
                        }
                    }
                } else {
                    $noWait = true;
                }

                if (($this->filepointer = touch($this->resource)) == false) {
                    throw new Exception('Lock file could not be created');
                }
            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 (unlink($this->resource) == false) {
                    $success = false;
                }
            break;
            case 'flock':
                if (flock($this->filepointer, LOCK_UN) == false) {
                    $success = false;
                }
                fclose($this->filepointer);
                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;
    }

    /**
     * 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, $severity=0) {
        t3lib_div::sysLog('Locking ['.$this->method.'::'.$this->id.']: '.trim($message), 'cms', $severity);
    }
}


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

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