Parallelizing Deadlock Resolution in Symbolic Synthesis of Distributed Programs

Previous work has shown that there are two major complexity barriers in the synthesis of fault-tolerant distributed programs: (1) generation of fault-span, the set of states reachable in the presence of faults, and (2) resolving deadlock states, from where the program has no outgoing transitions. Of these, the former closely resembles with model checking and, hence, techniques for efficient verification are directly applicable to it. Hence, we focus on expediting the latter with the use of multi-core technology. We present two approaches for parallelization by considering different design choices. The first approach is based on the computation of equivalence classes of program transitions (called group computation) that are needed due to the issue of distribution (i.e., inability of processes to atomically read and write all program variables). We show that in most cases the speedup of this approach is close to the ideal speedup and in some cases it is superlinear. The second approach uses traditional technique of partitioning deadlock states among multiple threads. However, our experiments show that the speedup for this approach is small. Consequently, our analysis demonstrates that a simple approach of parallelizing the group computation is likely to be the effective method for using multi-core computing in the context of deadlock resolution

Diconic addition of failsafe fault-tolerance

We present a divide-and-conquer method, called DiConic, for automatic addition of failsafe fault-tolerance to distributed programs, where a failsafe program guarantees to meet its safety specification even when faults occur. Specifically, instead of adding fault-tolerance to a program as a whole, we separately revise program actions so that the entire program becomes failsafe fault-tolerant. Our DiConic algorithm has the potential to utilize the processing power of a large number of machines working in parallel, thereby enabling automatic addition of failsafe fault-tolerance to distributed programs with a large number of processes. We formulate our DiConic synthesis algorithm in terms of the satisfiability problem and demonstrate our approach for the Byzantine Generals problem and an industrial application. Copyright 2007 ACM