// Parameters are the same as in the constructor.
func (d *dynamicSleeper) Update(factor float64, maxWait time.Duration) error {
	d.mu.Lock()
	defer d.mu.Unlock()
	if math.Abs(d.factor-factor) < 1e-10 && d.maxSleep == maxWait {
		return nil
	}
	// Update values and cycle waiting.
	xioutil.SafeClose(d.cycle)
	d.factor = factor
	d.maxSleep = maxWait
	d.cycle = make(chan struct{})