We give a formal specification and an implementation for a partitionable group communication service in asynchronous distributed systems. Our specification is motivated by the requirements for building “partition-aware ” applications that can continue operating without blocking in multiple concurrent partitions and reconfigure themselves dynamically when partitions merge. The specified service guarantees liveness and excludes trivial solutions; it constitutes a useful basis for building realistic partition-aware applications; and it is implementable in practical asynchronous distributed systems where certain stability conditions hold.

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We describe the design and implementation of Jgroup: a middleware system that integrates group technology with distributed objects and is based on Java RMI. Jgroup supports a programming paradigm called object groups and enables development of dependable network services based on replication. Among the novel features of Jgroup is a uniform object-oriented interface for programming both services and their clients. The fact that Jgroup exposes network effects, including partitions, to applications makes it particularly suitable for developing highly-available services in partitionable distributed systems. 1

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This tutorial gives a brief introduction to Java Remote Method Invocation, an overview and some details of the services provided by the Jgroup Group Communication System and explains how to develop distributed applications using Jgroup. It also gives a brief overview of the Autonomous Replication Management framework. 1

S. All local authors can be reached via e-mail at the address last-name@cs.unibo.it. Questions and comments should be addressed to tr-admin@cs.unibo.it. Recent Titles from the UBLCS Technical Report Series 96-16 Fault Tolerance through View Synchrony in Partitionable Asynchronous Distributed Systems, A. Montresor, December 1996. 96-17 A Tutorial on EMPA: A Theory of Concurrent Processes with Nondeterminism, Priorities, Probabilities and Time, M. Bernardo, R. Gorrieri, December 1996 (Revised January 1997). 97-1 Partitionable Group Membership: Specification and Algorithms, O. Babao glu, R. Davoli, A. Montresor, January 1997. 97-2 A Truly Concurrent View of Linda Interprocess Communication, N. Busi, R. Gorrieri, G. Zavattaro, February 1997. 97-3 Knowledge-Level Speech Acts, M. Gaspari, March 1997. 97-4 An Algebra of Actors, M. Gaspari, G. Zavattaro, May 1997. 97-5 On the Turing Equivalence of Linda Coordination Primitives, N. Busi, R. Gorrieri, G. Zavattaro, May 1997 (Revised October 19...

We present the design and implementation of a replication management framework for partition-aware applications based on Jgroup. Jgroup offers an extension to Java RMI based on the group communication paradigm, enabling development of dependable applications in partitionable distributed systems.

AbstractÐWe give a formal specification and an implementation for a partitionable group communication service in asynchronous distributed systems. Our specification is motivated by the requirements for building ªpartition-awareº applications that can continue operating without blocking in multiple concurrent partitions and reconfigure themselves dynamically when partitions merge. The specified service guarantees liveness and excludes trivial solutions, it constitutes a useful basis for building realistic partition-aware applications, and it is implementable in practical asynchronous distributed systems where certain stability conditions hold.