Discrete-Event Simulation and the Event Horizon Part 2: Event List Management

The event horizon is a very important concept that applies to both parallel and sequential discrete-event simulations. By exploiting the event horizon, parallel simulations can processes events optimistically in a risk-free manner (i.e., without requiring antimessages) using adaptable "breathing" time cycles with variable time widths. Additionally, exploiting the event horizon can significantly reduce the overhead of event list management that is common to virtually all discrete-event simulations. This paper is a continuation of work previously reported at PADS94. In that report, a complete mathematical formulation of the event horizon was derived under equilibrium conditions using the hold model. Various forms of the beta density function were consequently used to verify the predicted results of the analytic model. This second report describes how the concept of the event horizon can also be applied to event list management. By exploiting the event horizon, the performance of several priority queue data structures are improved including: linked lists, various binary trees, and heaps. A somewhat detailed description of these modified data structures along with other relevant background information is provided for completeness. Performance results for each of these priority queue data structure is provided.