Distributed Mutual Exclusion on a Ring of Processes

Abstract

A set of processes called "masters" are sharing a critical section on a mutual exclusion basis. The servers communicate with each other in a ring. Three solutions for solving the mutual exclusion problem are presented. They all rely on the presence of a unique privilege in the ring. The notation used extends CSP input and output commands with a Boolean primitive, the "probe", which makes it possible to determine whether a communication action is pending on a channel. A master communicates only with its private "server". In the correctness proofs, the concept of "trace" is introduced, i.e. a total ordering of actions corresponding to a possible interleaving of the atomic actions of a concurrent computation. [Note: report includes the date April 83/October 83 but published in 1984]