Consistent implementations of replicated objects

Shared objects are used in the distributed environment for synchronization, date sharing and service provision. They are usually replicated in a distr ibuted system for higher availability and fault tolerance. Coherent or stro ngly consistent implementation of replicated objects has been studied exten sively in the literature. This paper concentrates on a general method for s pecifying and implementing replicated objects that may require weaker consi stency conditions. The weakness of the objects is left open and users are a llowed to specify their objects by defining how concurrent sets of operatio ns should be performed. The implementation of a replicated object consists of two modules: one module is an algorithm to identify concurrent sets from a distributed computation and the other module is a user-defined procedure to process the concurrent sets. We show examples of weaker objects that ca n be defined and implemented more efficiently because of the less stringent requirements imposed on these objects. Several objects, including a shared dictionary, are used to demonstrate our scheme and we show that non-blocki ng implementations of some of these objects are possible.