code: func (tu *thresholdUpdater) Update(status error) {
  	tu.mu.Lock()
  	defer tu.mu.Unlock()
  
  	if status == nil {
  		tu.count = 0
  	} else if tu.count < tu.threshold {
  		tu.count++
  	}
  
  	tu.status = status
  }
docs: // thresholdUpdater implements the Updater interface, allowing asynchronous
  // access to the status of a Checker.