<?php

/**

 * Zend Framework

 *

 * LICENSE

 *

 * This source file is subject to the new BSD license that is bundled

 * with this package in the file LICENSE.txt.

 * It is also available through the world-wide-web at this URL:

 * http://framework.zend.com/license/new-bsd

 * If you did not receive a copy of the license and are unable to

 * obtain it through the world-wide-web, please send an email

 * to license@zend.com so we can send you a copy immediately.

 *

 * @category   Zend

 * @package    Zend_Search_Lucene

 * @copyright  Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)

 * @license    http://framework.zend.com/license/new-bsd     New BSD License

 * @version    $Id: LockManager.php 20096 2010-01-06 02:05:09Z bkarwin $

 */

/** Zend_Search_Lucene_Storage_Directory */

require_once 'Zend/Search/Lucene/Storage/Directory.php';

/** Zend_Search_Lucene_Storage_File */

require_once 'Zend/Search/Lucene/Storage/File.php';

/**

 * This is an utility class which provides index locks processing functionality

 *

 * @category   Zend

 * @package    Zend_Search_Lucene

 * @copyright  Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)

 * @license    http://framework.zend.com/license/new-bsd     New BSD License

 */

class Zend_Search_Lucene_LockManager

{

    /**

     * consts for name of file to show lock status

     */

    const WRITE_LOCK_FILE                = 'write.lock.file';

    const READ_LOCK_FILE                 = 'read.lock.file';

    const READ_LOCK_PROCESSING_LOCK_FILE = 'read-lock-processing.lock.file';

    const OPTIMIZATION_LOCK_FILE         = 'optimization.lock.file';

    /**

     * Obtain exclusive write lock on the index

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     * @return Zend_Search_Lucene_Storage_File

     * @throws Zend_Search_Lucene_Exception

     */

    public static function obtainWriteLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->createFile(self::WRITE_LOCK_FILE);

        if (!$lock->lock(LOCK_EX)) {

            require_once 'Zend/Search/Lucene/Exception.php';

            throw new Zend_Search_Lucene_Exception('Can\'t obtain exclusive index lock');

        }

        return $lock;

    }

    /**

     * Release exclusive write lock

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     */

    public static function releaseWriteLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->getFileObject(self::WRITE_LOCK_FILE);

        $lock->unlock();

    }

    /**

     * Obtain the exclusive "read escalation/de-escalation" lock

     *

     * Required to protect the escalate/de-escalate read lock process

     * on GFS (and potentially other) mounted filesystems.

     *

     * Why we need this:

     *  While GFS supports cluster-wide locking via flock(), it's

     *  implementation isn't quite what it should be.  The locking

     *  semantics that work consistently on a local filesystem tend to

     *  fail on GFS mounted filesystems.  This appears to be a design defect

     *  in the implementation of GFS.  How this manifests itself is that

     *  conditional promotion of a shared lock to exclusive will always

     *  fail, lock release requests are honored but not immediately

     *  processed (causing erratic failures of subsequent conditional

     *  requests) and the releasing of the exclusive lock before the

     *  shared lock is set when a lock is demoted (which can open a window

     *  of opportunity for another process to gain an exclusive lock when

     *  it shoudln't be allowed to).

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     * @return Zend_Search_Lucene_Storage_File

     * @throws Zend_Search_Lucene_Exception

     */

    private static function _startReadLockProcessing(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->createFile(self::READ_LOCK_PROCESSING_LOCK_FILE);

        if (!$lock->lock(LOCK_EX)) {

            require_once 'Zend/Search/Lucene/Exception.php';

            throw new Zend_Search_Lucene_Exception('Can\'t obtain exclusive lock for the read lock processing file');

        }

        return $lock;

    }

    /**

     * Release the exclusive "read escalation/de-escalation" lock

     *

     * Required to protect the escalate/de-escalate read lock process

     * on GFS (and potentially other) mounted filesystems.

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     */

    private static function _stopReadLockProcessing(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->getFileObject(self::READ_LOCK_PROCESSING_LOCK_FILE);

        $lock->unlock();

    }

    /**

     * Obtain shared read lock on the index

     *

     * It doesn't block other read or update processes, but prevent index from the premature cleaning-up

     *

     * @param Zend_Search_Lucene_Storage_Directory $defaultLockDirectory

     * @return Zend_Search_Lucene_Storage_File

     * @throws Zend_Search_Lucene_Exception

     */

    public static function obtainReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->createFile(self::READ_LOCK_FILE);

        if (!$lock->lock(LOCK_SH)) {

            require_once 'Zend/Search/Lucene/Exception.php';

            throw new Zend_Search_Lucene_Exception('Can\'t obtain shared reading index lock');

        }

        return $lock;

    }

    /**

     * Release shared read lock

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     */

    public static function releaseReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);

        $lock->unlock();

    }

    /**

     * Escalate Read lock to exclusive level

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     * @return boolean

     */

    public static function escalateReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        self::_startReadLockProcessing($lockDirectory);

        $lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);

        // First, release the shared lock for the benefit of GFS since

        // it will fail the conditional request to promote the lock to

        // "exclusive" while the shared lock is held (even when we are

        // the only holder).

        $lock->unlock();

        // GFS is really poor.  While the above "unlock" returns, GFS

        // doesn't clean up it's tables right away (which will potentially

        // cause the conditional locking for the "exclusive" lock to fail.

        // We will retry the conditional lock request several times on a

        // failure to get past this.  The performance hit is negligible

        // in the grand scheme of things and only will occur with GFS

        // filesystems or if another local process has the shared lock

        // on local filesystems.

        for ($retries = 0; $retries < 10; $retries++) {

            if ($lock->lock(LOCK_EX, true)) {

                // Exclusive lock is obtained!

                self::_stopReadLockProcessing($lockDirectory);

                return true;

            }

            // wait 1 microsecond

            usleep(1);

        }

        // Restore lock state

        $lock->lock(LOCK_SH);

        self::_stopReadLockProcessing($lockDirectory);

        return false;

    }

    /**

     * De-escalate Read lock to shared level

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     */

    public static function deEscalateReadLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->getFileObject(self::READ_LOCK_FILE);

        $lock->lock(LOCK_SH);

    }

    /**

     * Obtain exclusive optimization lock on the index

     *

     * Returns lock object on success and false otherwise (doesn't block execution)

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     * @return mixed

     */

    public static function obtainOptimizationLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->createFile(self::OPTIMIZATION_LOCK_FILE);

        if (!$lock->lock(LOCK_EX, true)) {

            return false;

        }

        return $lock;

    }

    /**

     * Release exclusive optimization lock

     *

     * @param Zend_Search_Lucene_Storage_Directory $lockDirectory

     */

    public static function releaseOptimizationLock(Zend_Search_Lucene_Storage_Directory $lockDirectory)

    {

        $lock = $lockDirectory->getFileObject(self::OPTIMIZATION_LOCK_FILE);

        $lock->unlock();

    }

}