if rt.maxParallelRequests < rt.parallelRequests {
		rt.maxParallelRequests = rt.parallelRequests
	}
	// increase the chance of collisions
	if rt.parallelRequestDelay > 0 {
		time.Sleep(rt.parallelRequestDelay)
	}
}

func (rt *requestTracker) incWithOptionalError() error {
	rt.Lock()
	defer rt.Unlock()
	rt.requests++
	if rt.err != nil && rt.requests >= rt.after {