Predetermined Rollbacks: An extension to Time Warp for spatially parallel agent-based simulation

Abstract

Time management is an important factor that affects the speed of parallel and distributed simulations. Conservative time management mechanisms advance simulation time after synchronization of logical processes, whereas optimistic time management mechanisms loosen synchronization among processes to speed up simulation. Because of loosened synchronization, the optimistic approaches are vulnerable to causality faults that must be addressed by logical processes during run-time. Repairing a simulation, by means of a rollback mechanism, is one of the most time-consuming processes of optimistic approaches. In this paper, we propose a method that considers precautionary measures against possible future rollbacks for Time Warp mechanism due to Jefferson. Our proposed method, named Predetermined Rollbacks, uses a modified simulation engine that can detect and avoid unnecessary rollbacks. Our experiments demonstrate that the proposed method can significantly improve the speedup of Time Warp in agent-based simulations, where agents communicate in a shared environment.