Abstract. Directed model checking is a well-established technique to efficiently tackle the state explosion problem when the aim is to find error states in concurrent systems. Although directed model checking has proved to be very successful in the past, additional search techniques provide much potential to efficiently handle larger and larger systems. In this work, we propose a novel technique for traversing the state space based on interference contexts. The basic idea is to preferably explore transitions that interfere with previously applied transitions, whereas other transitions are deferred accordingly. Our approach is orthogonal to the model checking process and can be applied to a wide range of search methods. We have implemented our method and empirically evaluated its potential on a range of non-trivial case studies. Compared to standard model checking techniques, we are able to detect subtle bugs with shorter error traces, consuming less memory and time. 1

Abstract. While exhaustive state space traversal is not feasible in reasonable time for complex concurrent programs, many techniques for efficient detection of concurrency errors and testing of concurrent programs have been introduced in recent years, such as directed search and context-bounded model checking. We propose to use depth-first traversal with randomized backtracking, where it is possible to backtrack from a state before all outgoing transitions have been explored, and the whole process is driven by random number choices. Experiments with a prototype implementation in JPF on several Java programs show that, in most cases, fewer states must be explored to find an error with our approach than using the existing techniques. 1

c t i v it y e p o r t

Abstract—The use of randomized backtracking in state space traversal is a technique for efficient detection of errors that we proposed recently. In this paper we summarize the basic approach and results of our initial experiments, and then we discuss possible extensions and optimizations. Keywords-state space traversal, randomization, backtracking, error detection, Java Pathfinder I.

Abstract. Directed model checking is a well-established technique for detecting error states in concurrent systems efficiently. As error traces are important for debugging purposes, it is preferable to find as short error traces as possible. A wide spread method to find provably shortest error traces is to apply the A ∗ search algorithm with distance heuristics that never overestimate the real error distance. An important class of such distance estimators is the class of pattern database heuristics, which are built on abstractions of the system under consideration. In this paper, we propose a systematic approach for the construction of pattern database heuristics. We formally define a concept to measure the accuracy of abstractions. Based on this technique, we address the challenge of finding abstractions that are succinct on the one hand, and accurate to produce informed pattern databases on the other hand. We evaluate our approach on large and complex industrial problems. The experiments show that the resulting distance heuristic impressively advances the state of the art. 1