andWainer G. Parallel environment for DEVS and Cell-DEVS models. Simulation 2007; 83: 449–471

Discrete Event System Specification (DEVS) is a sound formalism to describe generic dynamic sys-tems in a hierarchical and modular way. Cell-DEVS is a DEVS-based formalism intended to model complex physical systems as cell spaces. This work presents new techniques for executing DEVS and Cell-DEVS models in parallel and distributed environments based on the WARPED kernel, an im-plementation of the Time Warp protocol. The optimistic simulator PCD++, built as a new simulation engine for CD++, is a toolkit that implements the DEVS and Cell-DEVS formalisms. We redesign al-gorithms in CD++ to carry out optimistic simulations using a non-hierarchical approach that reduces the communication overhead. The message-passing organization is analyzed using a high-level ab-straction referred to as wall clock time slice. We propose a two-level user-controlled state-saving mechanism to achieve efficient and flexible state saving at runtime. Various optimization strategies are applied to PCD++ and their effects are analyzed quantitatively, including a risk-free message type-based state-saving strategy to reduce the number of states saved during the simulation sig-nificantly, and a one log file per node strategy to break the bottleneck caused by file I/O operations. It is shown that PCD++ markedly outperforms other alternatives and considerable speedups can be achieved in parallel and distributed simulations