code: func (c *CheckTTL) run() {
  	for {
  		select {
  		case <-c.timer.C:
  			c.Logger.Printf("[WARN] agent: Check %q missed TTL, is now critical",
  				c.CheckID)
  			c.Notify.UpdateCheck(c.CheckID, api.HealthCritical, c.getExpiredOutput())
  
  		case <-c.stopCh:
  			return
  		}
  	}
  }
docs: // run is used to handle TTL expiration and to update the check status