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Applications of a virtually synchronous environment are described for distributed programming, which underlies a collection of distributed programming tools in the ISIS2 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. It is argued 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.

This document describes applications of a new software abstraction called the virtually synchronous process group. Such a group consists of a set processes that cooperate to implement some distributed behavior in an environment where events like broadcasts to the group as an entity, process failures, and process recoveries appear to occur synchronously. The utility of this approach is illustrated by solving a number of classical problems using the authors methods. Many are problems that are quite difficult in the absence of some sort of support, and all are easily solved in the context of the mechanisms we propose here. They then describe a new version of the ISIS system, which is based on this abstraction. ISIS2 provides a number of high level mechanisms that facilitate the use of process groups in application software design, including addressing support atomic communication with the members of a single or several groups (even when their membership is changing), group RPC constructs, a package of distributed programming tools, a fault-tolerant asynchronous bulletin board mechanism, and resilient objects.

We describe applications of a new software abstraction called the virtually synchronous process group. Such a group consists of a set of processes that cooperate to implement some distributed behavior in an environment where events like broadcasts to the group as an entity, process failures, and process recoveries appear to occur synchronously. The utility of this approach is illustrated by solving a number of classical problems using our methods. Many are problems that are quite difficult in the absence of some sort of support, and all are easily solved in the context of the mechanisms we propose here. We then describe a new version of the ISIS system, which is based on this abstraction. ISIS2 provides a number of high level mechanisms that facilitate the use of process groups in application software design, including addressing support for atomic communication with the members of a single or several groups (even when their membership is changing), group RPC constructs, a package of distributed programming tools, a fault-tolerant asynchronous bulletin board mechanism, and resilient objects.

Applications of a virtually synchronous environment are described for distributed programming, which underlies a collection of distributed programming tools in the ISIS2 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. It is argued 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.