A Tight Bound on Time Complexity of Mutual Exclusion

In distributed shared memory multiprocessors, remote memory accesses generate processor-tomemory traffic which may result in a bottleneck. It is therefore important to design algorithms that minimize the number of remote memory accesses. We establish a lower bound of 3 on remote access time complexity for mutual exclusion algorithms in a model where processes communicate by means of a general read-modify-write primitive. Since a general read-modify-write primitive is a generalization of all atomic primitives that access at most one shared variable, our lower bound holds for any set of such primitives. Furthermore, this lower bound is tight because it matches the upper bound of Huang’s algorithm proposed in 1999.