Constraint Based Automated Synthesis of Nonmasking and Stabilizing Fault-Tolerance

We focus on constraint based automated addition of nonmasking and stabilizing fault-tolerance to hierarchical programs. We specify legitimate states of the program in terms of constraints that should be satisfied in those states. To deal with faults that may violate these constraints, we add recovery actions while ensuring interference freedom among the recovery actions added for satisfying different constraints. Since the constraint based manual design of fault tolerance is well known to be applicable in the manual design of nonmasking fault tolerance, we expect our approach to have a significant benefit in automation of fault tolerant programs. We illustrate our algorithms with three case studies: stabilizing mutual exclusion, stabilizing diffusing computation, and a data dissemination problem in sensor networks. With experimental results,we show that the complexity of synthesis is reasonable and that it can be reduced using the structure of the hierarchical systems. To our knowledge, this is the first instance where automated synthesis has been successfully used in synthesizing programs that are correct under fairness assumptions. Moreover, in two of the case studies considered in this paper, the structure of the recovery paths is too complex to permit existing heuristic based approaches for adding recovery.