Abstract

We address the problem of the impossibility of implementing synchronous fault-tolerant service specifications in asynchronous distributed systems. We introduce a method for weakening a synchronous service specification so that it becomes implementable in "timed" asynchronous systems, that is, asynchronous systems in which processes have access to local hardware clocks. The method (1) adds to a service interface an exception indicator so that a client knows at any time if a server is currently providing its standard "synchronous" semantics or some other specified exceptional semantics, (2) the standard behavior provided when the exception indicator does not signal an exception is "similar" to the original synchronous service behavior, and (3) a server has to provide its standard semantics whenever the underlying communication and process services exhibit "synchronous behavior ". To illustrate our method, we show how the specification of a synchronous datagram service and an internal clock synchronization service can be transformed into a fail-aware service specification. Further illustrations of the usefulness of fail-aware services are provided by describing a railway crossing service and a fail-aware weak group membership service.

Citations