Token-based read/write-locks for distributed mutual exclusion

Abstract

The contributions of this paper are twofold. First, a protocol for distributed mutual exclusion is introduced using a token-based decentralized approach, which allows either multiple concurrent readers or a single writer to enter their critical sections. This protocol utilizes a dynamic structure incorporating path compression to keep the messages overhead low resulting in an average complexity of O(log n) messages per request. Second, this protocol is evaluated in comparison with another protocol that uses a static structure instead of dynamic path compression. The measurements show that although concurrent readers may require at most one additional message per entry, the concurrent execution of critical sections results in faster responses of up to 30% for short critical sections. For longer critical sections, savings in the overall execution time increase with the fraction of readers to up to 50%. In particular applications with large fractions of readers, e.g., database queries, may exploit these benefits. The results further indicate that problems with fine-grained parallelism are more suitable for the dynamic protocol proposed here while the static protocol used for comparison performs equally well for coarse-grained parallelism. Overall, reader/writer distinction provides promising benefits in both cases.