Using message semantics to reduce rollback in the time warp mechanism

Abstract

The time warp mechanism is one of the most favorite paradigm to carry out a distributed discrete event simulation, where the synchronization of events can be determined a priori when the program is being executed. The forward computation performed optimistically has to be rolled back when an out-of-order synchronization message is received. This excessive amount of rollback often haunts the performance of a time warp mechanism. We propose in this paper that the semantics of the synchronization messages being sent in a time warp execution can be exploited to reduce the amount of rollback. In particular, we illustrate with some examples how the commutativity and dependency properties of messages can be used to avoid certain types of rollback. For example, two commutative messages can be processed in any order and the resultant computation remains valid. We present a protocol for message handling in the time warp mechanism. We also give a correctness argument for the protocol, leaving the formal proof in the full paper. In the discussion, we suggest several optimization techniques that can be used in our protocol for a better improvement.