Adding networks

Abstract

An adding network is a distributed data structure that supports a concurrent, lock-free, low-contention implementation of a fetch&add counter; a counting network is an instance of an adding network that supports only fetch&increment. We present a lower bound showing that adding networks have inherently high latency. Any adding network powerful enough to support addition by at least two values a and b, where |a| l> |b| > 0, has sequential executions in which each token traverses Ω(n/c) switching elements, where n is the number of concurrent processes, and c is a quantity we call one-shot contention; for a large class of switching networks and for conventional counting networks the one-shot contention is constant. On the contrary, counting networks have O(log n) latency [4,7]. This bound is tight. We present the first concurrent, lock-free, lowcontention networked data structure that supports arbitrary fetch&add operations.