code: func New(timeout time.Duration, timeoutFunc func()) *Heartbeat {
  	hb := &Heartbeat{
  		timeout: int64(timeout),
  		timer:   time.AfterFunc(timeout, timeoutFunc),
  	}
  	return hb
  }
docs: // New creates new Heartbeat with specified duration. timeoutFunc will be called
  // if timeout for heartbeat is expired. Note that in case of timeout you need to
  // call Beat() to reactivate Heartbeat.