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<?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) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
* @license http://framework.zend.com/license/new-bsd New BSD License
* @version $Id: LockManager.php 16971 2009-07-22 18:05:45Z mikaelkael $
*/
/** 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) 2005-2009 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();
}
}
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