关于$_SESSION存取的问题

    public static function onMessage($client_id, $message) {
        Gateway::setSession($client_id, );
        $all = Gateway::getAllClientSessions();
        echo "all session:\n";
        print_r($all);

  }

    public static function onClose($client_id) {
                $uid = isset($_SESSION) ?: 0;
                echo "close:::clientid:$client_id,uid:$uid\n";
    }

public static function onClose($client_id) {
    $uid = isset($_SESSION) ?$_SESSION: 0;
    echo "close:::clientid:$client_id,uid:$uid\n";
}