Global virtual time and distributed synchronization

Global Virtual Time (GVT) is the fundamental synchronization concept in optimistic simulations. It is defined as the earliest time tag within the set of unprocessed pending events in a distributed simulation. A number of techniques for determining GVT have been proposed in recent years, each having their own intrinsic properties. However, most of these techniques either focus on specific types of simulation problems or assume specific hardware support. This paper specifically addresses the GVT problem in the context of the following areas: Scalability, Efficiency, Portability, Flow control, Interactive support, Real time use. A new GVT algorithm, called SPEEDES GVT, has been developed in the Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES) framework. The new algorithm runs periodically but does not disrupt event processing. It provides flow control by processing events risk-free while flushing out messages during the GVT computation. SPEEDES GVT is built from a set of global reduction operations that are easily implementable on any hardware system