Concurrent Timestamping made simple

Abstract

Concurrent Timestamp Systems (ctss) allow processes to temporally order concurrent events in an asynchronous shared memory system. Bounded memory constructions of a ctss are extremely powerful tools for concurrency control, and are the basis for solutions to many coordination problems including mutual exclusion, randomized consensus, and multiwriter atomic registers. Unfortunately, known bounded ctss constructions seem to be complex from the algorithmic point of view. Due to the importance of bounded ctss, the rather involved original construction by Dolev and Shavit was followed by a series of papers that tried to provide more easily verifiable ctss constructions.

In this paper, we present what we believe is the simplest, most modular, and most easily proven bounded ctss algorithm known to date. The algorithm is constructed and its correctness proven using several tools. Our algorithm combines the labeling method of the Dolev-Shavit ctss with the atomic snapshot algorithm proposed in Afek et al. in a way that limits the amount of interleavings that can occur. We prove the correctness of our algorithm by showing that it implements a simple, unbounded, real-number based ctss specification. Our proof methodology is based on forward simulation techniques of the I/O Automata model.