Lukas Panneke

Nick Würdemann, Thomas Chatain, Stefan Haar et al.

Unfoldings are a well known partial-order semantics of P/T Petri nets that can be applied to various model checking or verification problems. For high-level Petri nets, the so-called symbolic unfolding generalizes this notion. A complete finite prefix of a P/T Petri net's unfolding contains all information to verify, e.g., reachability of markings. We unite these two concepts and define complete finite prefixes of the symbolic unfolding of high-level Petri nets. For a class of safe high-level Petri nets, we generalize the well-known algorithm by Esparza et al. for constructing small such prefixes. We evaluate this extended algorithm through a prototype implementation on four novel benchmark families. Additionally, we identify a more general class of nets with infinitely many reachable markings, for which an approach with an adapted cut-off criterion extends the complete prefix methodology, in the sense that the original algorithm cannot be applied to the P/T net represented by a high-level net.

Lukas Panneke, Heike Wehrheim

Folklore is often saying "The Java memory model is broken." Therefore, several approaches have proposed repairs, only to find new programs exhibiting unexpected, unintuitive behavior or the model forbidding standard compiler optimizations. The complexity of defining a memory model for concurrent Java lies in the fact that it requires a multi-execution model. Multi-execution models need to inspect the many potential executions of a program in order to find the valid ones. Tools automatically validating novel proposals of Java memory models are, however, largely lacking. To alleviate this problem, we introduce jMT, a novel tool for constructing multi-execution semantics for concurrent Java programs. jMT relies on single-execution models defining well-formed execution graphs, based on which it builds valid multi-execution semantics via causality checking. Thereby, jMT supports evaluating new proposals of Java memory models (JMMs) on a per-program basis. jMT can furthermore be employed for testing the conformance of JMMs to existing compilation schemes and compilers. Our evaluation of jMT on 169 litmus tests reveals a number of interesting insights into existing JMMs.