Copies convergence in a distributed real-time collaborative environment

Abstract

In real-time collaborative systems, replicated objects, shared by users, are subject to concurrency constraints. In order to satisfy these, various algorithms, qualified as optimistic, [3, 5, 13, 17, 14, 15, 18], have been proposed that exploit the semantic properties of operations to serialize concurrent operations and achieve copy convergence of replicated objects. Their drawback is that they either require a condition on user's operations which is hard to verify when possible to ensure, or they need undoing then redoing operations in some situations. The main purpose of this paper is to present two new algorithms that overcome these drawbacks. They are based upon the implementation of a continuous global order which enables that condition to be released, and simplifies the operation integration process. In the second algorithm, thanks to deferred broadcast of operations to other sites, this process becomes even more simplified.