Atomic Distributed Semaphores for Accessing Networked Data

Distributed hash tables (DHTs), based on consistent hashing, offer efficient lookup services for decentralized distributed systems. DHTs operate efficiently to handle large number of network nodes with continual node arrivals, departures, and failures. Upon addressing the crucial issues of communication efficiency and offering load balancing in dynamic networking environments, DHTs are the essential components for building structured peer-to-peer (P2P) overlay networks. Although structured overlays improve data availability and consistency, they do not provide strong semantics on distributed data mutual exclusion operations. For a robust network operating system, it is essential to provide atomic data access semantic services. In this paper, a distributed semaphore (DISEM) mechanism is proposed, and it is designed on top of a dynamic structured overlay. The proposed design circumvents the availability and consistency issues. Independent of any underlying overlay algorithms, DISEM provides a tunable level of data availability and consistency, while offering fault tolerance and reliable delivery services. A testbed prototype has been implemented to validate the mutual exclusiveness of networked replicas under different traffic loadings. The measured results indicate that DISEM offers high mutual exclusive access rates under different networking conditions.