A generalised sweep-line method for safety properties

Abstract

The recently developed sweep-line method exploits progress present in many concurrent systems to explore the full state space of the system while storing only small fragments of the state space in memory at a time. A disadvantage of the sweep-line method is that it relies on a monotone and global notion of progress. This prevents the method from being used for many reactive systems. In this paper we generalise the sweep-line method such that it can be used for verifying safety properties of reactive systems exhibiting local progress. The basic idea is to relax the monotone notion of progress and to recognise the situations where this could cause the state space exploration not to terminate. The generalised sweep-line method explores all reachable states of the system, but may explore a state several times. We demonstrate the practical application of the generalised sweep-line method on two case studies demonstrating a reduction in peak memory usage to typically 10% compared to the use of ordinary full state spaces.