Exploiting virtual synchrony in distributed systems

We describe applications of a virtually synchronous environment for distributed programming, which underlies a collection of distributed programming tools in the ISIS 2 system. A virtually synchronous environment allows processes to be structured into process groups , and makes events like broadcasts to the group as an entity, group membership changes, and even migration of an activity from one place to another appear to occur instantaneously — in other words, synchronously. A major advantage to this approach is that many aspects of a distributed application can be treated independently without compromising correctness. Moreover, user code that is designed as if the system were synchronous can often be executed concurrently. We argue that this approach to building distributed and fault-tolerant software is more straightforward, more flexible, and more likely to yield correct solutions than alternative approaches.