Approximate verification of concurrent systems using token structures and invariants

Distributed systems often rely on token structures to avoid undesired states and behave correctly. While conservative token structures ensure that a fixed number of tokens exist at all times, existential structures guarantee that tokens cannot be completely eliminated. In this paper, we show how a SAT/SMT checker can be used to automatically detect such token structures in concurrent systems and how to derive the natural invariants they preserve. We use these invariants to improve the precision of a deadlock-checking framework that is based on local analysis. Moreover, we conducted some practical experiments to demonstrate that this new framework is as efficient as similar incomplete techniques for deadlock-freedom analysis while handling a different class of systems.