Automatic Addition of Fault-Tolerance in Presence of Unchangeable Environment Actions .

We focus on the problem of adding fault-tolerance to an existing concurrent protocol in the presence of unchangeable environment actions. Such unchangeable actions occur in cases where a subset of components/processes cannot be modified since they represent third-party components or are constrained by physical laws. These actions differ from faults in that they are (1) simultaneously collaborative and disruptive, (2) essential for satisfying the specification and (3) possibly non-terminating. Hence, if these actions are modeled as faults while adding fault-tolerance, it causes existing model repair algorithms to declare failure to add fault-tolerance. We present a set of algorithms for adding stabilization and fault-tolerance for programs that run in the presence of environment actions. We prove the soundness, completeness and the complexity of our algorithms. We have implemented all of our algorithms using symbolic techniques in Java. The experimental results of our algorithms for various examples are also provided.