Effective Access to the Committed Global State in Speculative Parallel Discrete Event Simulation on Multi-core Machines

Output production and predicate detection are critical in speculative parallel discrete event simulation, since they need to take place accessing past state values-which have become committed-rather than the current state of the simulation objects, which is possibly affected by causality errors related to speculative event processing. In this article, we present an architecture that enables an effective management of the access to the committed state of any simulation object while still guaranteeing: (i) minimal impact on the forward execution of the simulation in terms of synchronization (and roll-back generation) and (ii) highly balanced distribution of the tasks among all the threads running the simulation application. Our architecture is devised for speculative simulation engines running on top of shared-memory parallel machines, where worker threads full share the simulation workload. We exploit kernel-level facilities-targeting the Linux operating system-and user level ones, which work together for enabling a suited wall-clock-time collocation of the threads' activities for the access to the committed global state of the simulation. We integrated our proposal within the USE (Ultimate Share-Everything) open-source simulation platform, and provide an experimental assessment of it.