Group communication in partitionable distributed systems

We give a formal specification and an implementation for a partitionable gr oup communication service in asynchronous distributed systems. Our specific ation is motivated by the requirements for building "partition-aware" appli cations that can continue operating without blocking in multiple concurrent partitions and reconfigure themselves dynamically when partitions merge. T he specified service guarantees liveness and excludes trivial solutions; it constitutes a useful basis for building realistic partition-aware applicat ions; and it is implementable in practical asynchronous distributed systems where certain stability conditions hold.