心跳机制的发送间隔

    // 如果有设置心跳，则定时执行
    if($this->pingInterval > 0)
    {
        $timer_interval = $this->pingNotResponseLimit > 0 ? $this->pingInterval/2 : $this->pingInterval;
        Timer::add($timer_interval, array($this, 'ping'));
    }