Non-intrusive Repair of Safety and Liveness Violations in Reactive Programs

We show how, under certain conditions, programs written in the behavioral programming approach can be modified (e.g., as a result of new requirements or discovered bugs) using automatically-generated code modules. Given a trace of undesired behavior, one can generate a relatively small piece of code, whose execution is interwoven at run time with the rest of the system, and which brings about the desired changes without modifying existing code and without introducing new bugs. At the core of our approach is the ability of a thread of behavior to prevent the triggering of events from other threads. Our repair algorithms apply model checking of safety and liveness properties to the program and transform the counterexamples produced by the model-checker into corrective modules. The work is supported by a proof-of-concept tool, which creates understandable modules that can be further manually managed as part of a process of ongoing incremental system development.