Developing and refining an adaptive token-passing strategy

Token rotation algorithms play an important role in distributed computing, to support such activities as mutual exclusion, round-robin scheduling, group membership and group communication protocols. Ring-based protocols maximize throughput in busy systems but can incur a linear (in the number of processors) delay when a processor needs to obtain a token to perform an operation. This paper synthesizes new algorithmic techniques for improving the performance (responsiveness) of logical ring protocols. The parameterized technique presents the safety properties of ring protocols and maintains high throughput in busy systems, while reducing the delay in lightly loaded systems from a linear to a logarithmic function in the number of processors. The development in this paper is done using term rewriting systems, where our parameterized protocol is developed in a series of safety-preserving refinements of a basic specification.