code: function event(string $event, callable $callback) {
          if (self::$_status > self::_STATUS_INITIAL) {
              Console::warning('Cannot set event callback once the service is started.');
              return;
          }
          if (!is_callable($callback)) {
              Console::warning('Failed to set event callback. Not callable.');
              return;
          }
          switch ($event) {
              case 'WorkerStart':
                  $this->_on_start = $callback;
                  break;
              case 'WorkerStop':
                  $this->_on_stop = $callback;
                  break;
              case 'Message':
                  $this->_on_message = $callback;
                  break;
              default:
                  $this->_worker->{'on'.$event} = $callback;
          }
      }
docs: 绑定事件回调
  
  @param string $event
  @param callable $callback