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<?php
/**
* StudipLock.class.php
* class with methods to perform cooperative advisory locking
* using the GET_LOCK feature from Mysql
* https://dev.mysql.com/doc/refman/5.0/en/miscellaneous-functions.html#function_get-lock
*
* This program 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.
*
* @author André Noack <noack@data-quest.de>
* @copyright 2013 Stud.IP Core-Group
* @license http://www.gnu.org/licenses/gpl-2.0.html GPL version 2
* @category Stud.IP
*/
class StudipLock
{
/**
* name of active lock
* @var string
*/
private static $current;
/**
* returns the name of the current active lock
* @return string name of active lock
*/
public static function getCurrent()
{
return self::$current;
}
/**
* Tries to obtain a lock with a name given by the string $lockname,
* using a timeout of $timeout seconds. Returns 1 if the lock was obtained
* successfully, 0 if the attempt timed out
* (for example, because another client has previously locked the name),
* or NULL if an error occurred
* If a name has been locked by one client, any request by another client
* for a lock with the same name is blocked.
*
* @param string $lockname
* @param number $timeout in seconds
* @throws UnexpectedValueException if there is already an active lock
* @return integer 1 if the lock was obtained successfully, 0 if the attempt timed out
*/
public static function get($lockname, $timeout = 10)
{
if (self::$current !== null) {
throw new UnexpectedValueException(sprintf('could not acquire new lock, %s still active'));
}
$ok = DBManager::get()->fetchColumn("SELECT GET_LOCK(?,?)", [self::lockname($lockname), $timeout]);
if ($ok) {
self::$current = $lockname;
}
return $ok;
}
/**
* check if lock with given name is available
*
* @param string $lockname
* @return integer 1 if lock is available
*/
public static function isFree($lockname)
{
return DBManager::get()->fetchColumn("SELECT IS_FREE_LOCK(?)", [self::lockname($lockname)]);
}
/**
* release the current lock
*
* @return integer 1 if the lock could be released
*/
public static function release()
{
if (self::$current) {
return DBManager::get()->fetchColumn("SELECT RELEASE_LOCK(?)", [self::lockname(self::$current)]);
}
}
/**
* prepends the name of current database to lockname
* because locks are server-wide
*
* @param string $lockname
* @return string
*/
public static function lockname($lockname)
{
return $GLOBALS['DB_STUDIP_DATABASE'] . '_' . $lockname;
}
}
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