React\Mysql传入WorkerMan的$loop报错

$loop     = Worker::getEventLoop();
// $loop     = React\EventLoop\Factory::create();
self::$db = new React\MySQL\Connection($loop, array(
    'host'   => DBHOST,
    'dbname' => DBNAME,
    'user'   => DBUSER,
    'passwd' => DBPASS,
));