Fast and Scalable Group Mutual Exclusion

The group mutual exclusion (GME) problem is a generalization of the classical mutual exclusion problem in which every critical section is associated with a type or session. Critical sections belonging to the same session can execute concurrently, whereas critical sections belonging to different sessions must be executed serially. The well-known read-write mutual exclusion problem is a special case of the group mutual exclusion problem. In this work, we present a novel GME algorithm for an asynchronous shared-memory system that, in addition to satisfying lockout freedom, bounded exit and concurrent entering properties, has O(1) step-complexity when the system contains no conflicting requests as well as O(1) space-complexity per GME object when the system contains sufficient number of GME objects. To the best of our knowledge, no existing GME algorithm has O(1) step-complexity for concurrent entering. Moreover, most existing GME algorithms have {\Omega}(n) space complexity per GME object, where n denotes the number of processes in the system. We also show that our GME algorithm can be easily modified to use bounded space variables.