A formal framework for specifying and verifying time warp optimizations

Abstract

Parallel and distributed systems are representative of large and complex systems that require the application of formal methods. These systems are often unreliable because implementors design and develop these systems without a complete understanding of the problem domain; in addition, the nondeterministic nature of certain parallel and distributed systems make system validation difficult if not impossible. To address this issue, the application of formal specification and verification to a class of parallel and distributed software systems is presented in this paper. Specifically, the Prototype Verification System (PVS) is applied to the specification and verification of the Time Warp protocol, a distributed optimistic discrete event simulation algorithm. The paper discusses how the specification of the Time Warp protocol can be mechanized within a general-purpose higher-order theorem proving framework like PVS. In addition, the paper presents the extensibility of the specification to address and verify different aspects and optimizations of the basic Time Warp protocol. As an illustrative example, our experiences in specifying and verifying the infrequent state saving optimization to the basic Time Warp protocol is reported in the paper.