Context-Bounded Model Checking of Concurrent Software

The interaction among concurrently executing threads of a program results in insidious programming errors that are difficult to reproduce and fix. Unfortunately, the problem of verifying a concurrent boolean program is undecidable [24]. In this paper, we prove that the problem is decidable, even in the presence of unbounded parallelism, if the analysis is restricted to executions in which the number of context switches is bounded by an arbitrary constant. Restricting the analysis to executions with a bounded number of context switches is unsound. However, the analysis can still discover intricate bugs and is sound up to the bound since within each context, a thread is fully explored for unbounded stack depth. We present an analysis of a real concurrent system by the zing model checker which demonstrates that the ability to model check with arbitrary but fixed context bound in the presence of unbounded parallelism is valuable in practice. Implementing contextbounded model checking in zing is left for future work.