Conjunctive Predicate Detection

This paper discusses eecient detection of global predicates in a distributed program. Previous work in detection of global predicates was restricted to predicates that could be speciied as a boolean formula of local predicates. Many properties in distributed systems, however, use the state of channels. In this paper, we introduce the concept of a channel predicate and provide an eecient algorithm to detect any boolean formula of local and channel predicates. We deene a property called monotonicity for channel predicates. Monotonicity is crucial for eecient detection of global predicates. We show that many problems studied earlier, such as detection of termination and computation of global virtual time are special cases of the problem considered in this paper. The message complexity of our algorithm is bounded by the number of messages used by the program. The main application of our results are in debug-ging and testing of distributed programs. Our algorithms have been incorporated in a distributed programming environment which runs on a network of IBM RS/6000 Workstations under AIX with the PVM environment.