Mutual exclusion is one of the well-studied fundamental primitives in distributed systems, and a number of vital solutions have been proposed to achieve the same. However, the emerging Peer to Peer systems bring forward several challenges to protect consistent and concurrent access to shared resources, as classical peer-to-peer systems, like Napster, Gnutella, et cetera, have been mainly used for sharing files with read only permission. In this chapter, the authors propose a quorum based mutual exclusion algorithm that can be used over any Peer to Peer Distributed Hash Table (DHT). The proposed approach can be seen as extension to traditional Sigma protocol for mutual exclusion in Peer to Peer systems. The basic idea is to reduce message overhead with use of smart nodes present in each quorum set and message passing between the current owners of resource with next resource requester nodes.
A Fault-tolerant Mutual Exclusion Algorithm in Asynchronous Distributed Systems