Robust distributed mutual exclusion

A token based algorithm for distributed mutual exclusion is presented. It uses a distributed counter to tolerate faults due to site failures and communication failures. This eliminates the need for expensive election protocols that are commonly employed in existing token-based algorithms. As in many existing fault-tolerant mutual exclusion algorithms, timeouts are used to detect failures. Our algorithm has the unique property that even if timeout periods are incorrectly assumed, the safety requirement of mutual exclusion is still guaranteed. It is, therefore, suitable for highly asynchronous distributed environments. Performance analysis shows that the algorithm is also efficient in terms of the average number of messages required per critical section, and the average time delay to enter the critical section. Finally, we show how to obtain a bounded algorithm from the basic unbounded algorithm.