Wordpress Comet缓存在session_start（）之后第一次没有启动？

I am using this code and after first entry of new user to page comet cache will not send cached content.

$status = session_status();
if($status == PHP_SESSION_NONE){
    session_start();
}
if (isset($_SESSION['comparison']) && is_array($_SESSION['comparison']) && count($_SESSION['comparison'])>0){
            define('DONOTCACHEPAGE', TRUE);
    }