function onServerStop(Worker $worker) {
        if (is_callable($this->_on_stop))
            call_user_func($this->_on_stop, $worker);
    }
function onServerStop(Worker $worker) {
        if (is_callable($this->_on_stop))
            call_user_func($this->_on_stop, $worker);
    }
服务停止回调

@param Worker $worker