public static function __shutdownCleanup()
    {
        $now = time();

        if (is_array(self::$lockFiles)) {
            foreach (self::$lockFiles as $lockFile => $meta) {
                if (($now - $meta['time'] > $meta['ttl']) && file_exists($lockFile)) {
                    unlink($lockFile);
                }
            }
        }
    }