Stabilization and fault-tolerance in presence of unchangeable environment actions

Abstract

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 algorithms to declare failure to add fault-tolerance. We present algorithms for adding stabilizing and fault-tolerance. Since previous approaches for adding stabilizing and fault-tolerance to (disruptive and eventually terminating) faults cannot be extended for environment actions, we develop new algorithms that are sound, complete and in P (in the state space).