Producing Scheduling that Causes Concurrent Programs to Fail

A noise maker is a tool that seeds a concurrent program with conditional synchronization primitives (such as yield()) for the purpose of increasing the likelihood that a bug manifest itself. This work explores the theory and practice of choosing where in the program to induce such thread switches at runtime. We introduce a novel fault model that classifies locations as .good., .neutral., or .bad,. based on the effect of a thread switch at the location. Using the model we explore the terms in which efficient search for real-life concurrent bugs can be carried out. We accordingly justify the use of probabilistic algorithms for this search and gain a deeper insight of the work done so far on noise-making. We validate our approach by experimenting with a set of programs taken from publicly available multi-threaded benchmark. Our empirical evidence demonstrates that real-life behavior is similar to what our model predicts

Controllability problems in MSC-based testing

This is a pre-copyedited, author-produced PDF of an article accepted for publication in The Computer Journal following peer review. The definitive publisher-authenticated version [Dan, H and Hierons, RM (2012), "Controllability Problems in MSC-Based Testing", The Computer Journal, 55(11), 1270-1287] is available online at: http://comjnl.oxfordjournals.org/content/55/11/1270. Copyright @ The Authors 2011.In testing systems with distributed interfaces/ports, we may place a separate tester at each port. It is known that this approach can introduce controllability problems which have received much attention in testing from finite state machines. Message sequence charts (MSCs) form an alternative, commonly used, language for modelling distributed systems. However, controllability problems in testing from MSCs have not been thoroughly investigated. In this paper, controllability problems in MSC test cases are analysed with three notions of observability: local, tester and global. We identify two types of controllability problem in MSC-based testing. It transpires that each type of controllability problem is related to a type of MSC pathology. Controllability problems of timing are caused by races but not every race causes controllability problems; controllability problems of choice are caused by non-local choices and not every non-local choice causes controllability problems. We show that some controllability problems of timing are avoidable and some controllability problems of choice can be overcome when testers have better observational power. Algorithms are provided to tackle both types of controllability problems. Finally, we show how one can overcome controllability problems using a coordination service with status messages based on algorithms developed in this paper.EPSR

Post-Election Audits: Restoring Trust in Elections

With the intention of assisting legislators, election officials and the public to make sense of recent literature on post-election audits and convert it into realistic audit practices, the Brennan Center and the Samuelson Law, Technology and Public Policy Clinic at Boalt Hall School of Law (University of California Berkeley) convened a blue ribbon panel (the "Audit Panel") of statisticians, voting experts, computer scientists and several of the nation's leading election officials. Following a review of the literature and extensive consultation with the Audit Panel, the Brennan Center and the Samuelson Clinic make several practical recommendations for improving post-election audits, regardless of the audit method that a jurisdiction ultimately decides to adopt