Unfolding-Based Dynamic Partial Order Reduction of Asynchronous Distributed Programs

Abstract

Unfolding-based Dynamic Partial Order Reduction (UDPOR) is a recent technique mixing Dynamic Partial Order Reduction (DPOR) with concepts of concurrency such as unfoldings to efficiently mitigate state space explosion in model-checking of concurrent programs. It is optimal in the sense that each Mazurkiewicz trace, i.e. a class of interleavings equivalent by commuting independent actions, is explored exactly once. This paper shows that UDPOR can be extended to verify asynchronous distributed applications, where processes both communicate by messages and synchronize on shared resources. To do so, a general model of asynchronous distributed programs is formalized in TLA+. This allows to define an independence relation, a main ingredient of the unfolding semantics. Then, the adaptation of UDPOR, involving the construction of an unfolding, is made efficient by a precise analysis of dependencies. A prototype implementation gives promising experimental results.