A Dynamic Group Mutual Exclusion Algorithm Using Surrogate-Quorums

Abstract

The group mutual exclusion problem extends the traditional mutual exclusion problem by associating a type with each critical section. In this problem, processes requesting critical sections of the same type can execute their critical sections concurrently. However, processes requesting critical sections of different types must execute their critical sections in a mutually exclusive manner. In this paper, we provide a distributed algorithm for solving the group mutual exclusion problem based on the notion of surrogate-quorum. Intuitively, the algorithm uses the quorum that has been successfully locked by a request as a surrogate to service other compatible requests for the same type of critical section. Unlike the existing quorum-based algorithms for group mutual exclusion, the algorithm achieves a low message complexity of O(q), where q is the maximum size of a quorum, while maintaining both synchronization delay and waiting time at two message hops. Moreover, like the existing quorum-based algorithms, the algorithm has high maximum concurrency of n, where n is the number of processes in the system. The existing quorum-based algorithms assume that the number of groups is static and does not change during runtime. However, the algorithm can adapt without performance penalties to dynamic changes in the number of groups. Simulation results indicate that our algorithm outperforms the existing quorum-based algorithms for group mutual exclusion by as much as 50% in some cases