Efficient Detection of Channel Predicates in Distributed Systems

This paper discusses efficient detection of global predicates in a distributed program. Previous work in this area required predicates to be specified as a conjunction of predicates defined on individual processes. Many properties in distributed systems, however, use the state of channels such as “the channel is empty,” or “there is a token in the channel”. In this paper, we introduce the concept of a linear channel predicate and provide efficient centralized and distributed algorithms to detect any conjunction of local and linear channel predicates. The class of linear predicates is fairly broad. For example, classic problems such as detection of termination and computation of global virtual time are instances of conjunctions of linear channel predicates. Linear predicates can be functions of the number of messages in the channel, or can be based upon the actual contents of the messages. The main application of our results are in debugging and testing of distributed programs. For these applications it is important to detect the first state where some predicate is true. We show that this first state is uniquely defined if and only if linear predicates are used.