State saving for interactive optimistic simulation

Abstract

Time Warp's optimistic scheduling requires the maintenance of simulation state history to support rollback in the event of causality violations. State history, and the ability to rollback the simulation, can provide unique functionality for human-in-the-loop simulation environments. This paper investigates the use of Time Warp to output valid simulation state in a near real-time manner, re-execute portions of the simulation, and interactively probe simulation values to ascertain underlying causes of transient behavior.A shared-memory, multi-threaded interactive simulation architecture is presented and the additional state saving requirements imposed by interactivity are examined. The shortcomings of existing state saving schemes lead us to propose Multiplexed State Saving (MSS). By interleaving checkpointing and incremental state logs MSS provides bounded rollback costs and asynchronous access to prior simulation state. The interaction algorithms and MSS form a scalable, bounded cost component suitable for use in a real-time interactive Time Warp system.

Cloning parallel simulations

“…Related work in interactive parallel discrete event simulation is described in [Steinman 1991] and in [Franks et al 1997]. In [Steinman 1991] a message type called an external event enables interaction with the simulator.…”

“…These events can steer, sample and query the simulation in progress. The approach of [Franks et al 1997] allows for the testing of what-if scenarios provided they are interjected before a deadline. Alternatives are examined sequentially by using a rollback mechanism to erase exploration of one path in order to begin exploration of another.…”

Latency Hiding with Optimistic Computations

“…Related work in interactive parallel discrete event simulation is described in [4,7,12]. In [12] a message type referred to as an external event enables interaction with the simulator.…”

“…These events can steer, sample, and query the simulation in progress. The approach of [4] allows for the testing of what-if scenarios provided they are interjected before a deadline. Ghosh's approach enables optimistic computations in a real-time environment by avoiding sending incorrect messages [7].…”

Event history based sparse state saving in time warp

“…In order to guarantee the reconstructability of past states, Time Warp simulators are provided with well known checkpointing schemes such as copy, sparse and incremental state saving (recently schemes that mix features of both sparse and incremental approaches have been proposed in [6,181).…”