ToMAL: Token-Based Fair Mutual Exclusion Algorithm

Abstract

Token-based mutual exclusion (ME) algorithms for distributed systems have gained much attention over the years due to their inherent safety property. Safety property ensures that only one process executes the critical section at any instant of time. Raymond, et al. have proposed a token-based ME algorithm that uses an inverted-tree topology. The solution is simple, fast, and widely accepted by the community. However, a major drawback of Raymond’s algorithm is that it fails to satisfy the fairness property in terms of the first-come-first-serve policy among equal-priority processes requesting the token. Several attempts have been initiated to resolve this issue. In this work, we provide a new token-based ME algorithm (ToMAL) that, similar to Raymond’s algorithm, works on inverted tree topology. The proposed solution not only ensures the fairness property but also requires very little additional storage in a node. We have compared our proposed approach ToMAL with another existing work. The comparative performances are studied in terms of storage space and control messages.