func (l *requestFIFO) Length() int {
	return l.Len()
}

func (l *requestFIFO) QueueSum() queueSum {
	return l.sum
}

func (l *requestFIFO) Enqueue(req *request) removeFromFIFOFunc {
	e := l.PushBack(req)
	addToQueueSum(&l.sum, req)

	return func() *request {
		if e.Value == nil {
			return nil
		}
		l.Remove(e)
		e.Value = nil
		deductFromQueueSum(&l.sum, req)
		return req
	}
}