public function set_as_session_store($session_expire_time = null)
    {
        if ($session_expire_time != null) {
            $this->session_expire_time = $session_expire_time;
        }
        session_set_save_handler(
            array($this, 'session_open'),
            array($this, 'session_close'),
            array($this, 'session_read'),
            array($this, 'session_write'),
            array($this, 'session_destroy'),
            array($this, 'session_gc')
        );
    }