Scoped Synchronization Constraints for Large Scale Actor Systems

Very large scale systems of autonomous concurrent objects (Actors) require coordination models to meet two competing goals. On the one hand, the coordination models must allow Actors to dynamically modify protocols in order to adapt to requirement changes over the, likely extensive, lifetime of the system. On the other hand, the coordination models must enforce protocols on potentially uncooperative Actors, while preventing deadlocks caused by malicious or faulty Actors. To meet these competing requirements, we introduce a novel, scoped semantics for Synchronizers [7,6]--a coordination model based on declarative synchronization constraints. The mechanism used to limit the scope of the synchronization constraints is based on capabilities and works without central authority. We show that the mechanism closes an attack vector in the original Synchronizer approach which allowed malicious Actors to intentionally deadlock other Actors.