php如何获取所有的sessionid或获取所有的session？

print_r($_SESSION);
print_r($_SESSION);

	class Session {		
	private static $handler=null;		
	private static $ip=null;		
	private static $lifetime=null;		
	private static $time=null;//初始化变量；		
	private static function init($handler){			
	self::$handler=$handler;			
	//$_SERVER["REMOTE_ADDR"]获取客户端路由地址；			
	self::$ip = !empty($_SERVER["REMOTE_ADDR"]) ? $_SERVER["REMOTE_ADDR"] : 'unknown';			
	//ini_get()获取配置文件变量；			
	self::$lifetime=ini_get('session.gc_maxlifetime');			
	self::$time=time();		
	}		
	static function start(PDO $pdo){			
	self::init($pdo);			
	//_CLASS_  代表本类；			
	session_set_save_handler(					
	array(__CLASS__,"open"),					
	array(__CLASS__,"close"),					
	array(__CLASS__,"read"),					
	array(__CLASS__,"write"),					
	array(__CLASS__,"destroy"),					
	array(__CLASS__,"gc")				
	);			
	session_start();		
	}		
	public static function open($path, $name){			
	return true;		
	}		
	public static function close(){			
	return true;		
	}				
	public static function read($PHPSESSID){			
	$sql="select PHPSESSID, update_time, client_ip, data from session where PHPSESSID= ?";			
	$stmt=self::$handler->prepare($sql);			
	$stmt->execute(array($PHPSESSID));						
	if(!$result=$stmt->fetch(PDO::FETCH_ASSOC)){				
	return '';			
	}			
	if( self::$ip  != $result["client_ip"]){				
	self::destroy($PHPSESSID);				
	return '';			
	}			
	if(($result["update_time"] + self::$lifetime) prepare($sql);			
	$stmt->execute(array($PHPSESSID));			
	if($result=$stmt->fetch(PDO::FETCH_ASSOC)){				
	if($result['data'] != $data || self::$time > ($result['update_time']+30)){					
	$sql="update session set update_time = ?, data =? where PHPSESSID = ?";										
	$stm=self::$handler->prepare($sql);					
	$stm->execute(array(self::$time, $data, $PHPSESSID));								
	}			
	}else{				
	if(!empty($data)){					
	$sql="insert into session(PHPSESSID, update_time, client_ip, data) values(?,?,?,?)";					
	$sth=self::$handler->prepare($sql);					
	$sth->execute(array($PHPSESSID, self::$time, self::$ip, $data));				
	}			
	}			
	return true;		
	}		
	public static function destroy($PHPSESSID){			
	$sql="delete from session where PHPSESSID = ?";			
	$stmt=self::$handler->prepare($sql);			
	$stmt->execute(array($PHPSESSID));			
	return true;		
	}		
	private static function gc($lifetime){			
	$sql = "delete from session where update_time prepare($sql);			
	$stmt->execute(array(self::$time-$lifetime));			
	return true;		
	}		
	}	
	try{		
	$pdo=new PDO("mysql:host=localhost;dbname=xsphpdb", "root", "123456");	
	}catch(PDOException $e){		
	echo $e->getMessage();	}	
	Session::start($pdo);

echo session_id()