Data Requirements for Implementation of N-Process Mutual Exclusion Using a Single Shared Variable

Abstract

An analysis is made of the shared memory requirements for implementing mutual excluslon of N asynchronous parallel processes m a model where the only primitive communication mechamsm is a general test-and-set operation on a single shared variable. While two variable values suffice to tmplement simple mutual exclusion without deadlock, it is shown that any solution whJch avoids possJble lockout of processes requires at least 2i + values A technical restnctmn on the model increases this requtrement to N/2 values, while achieving a fixed bound on wamng further increases the reqmrement to N + 1 values. These bounds are shown to be nearly optimal, for algorithms are exhibited for the last two cases which use [N/2J + 9 and N + 3 values, respectively All of the lower bounds apply afortiori to the space requirements for weaker primitives, such as P and V, using busy waiting. © 1982, ACM. All rights reserved.