Mobile Barriers for occam-pi: Semantics, Implementation and Application

This paper introduces a safe language binding for CSP multiway events (barriers -- both static and mobile) that has been built into occam-pi (an extension of the classical occam language with dynamic parallelism, mobile processes and mobile channels). Barriers provide a simple way for synchronising multiple processes and are the fundamental control mechanism underlying both CSP (Communicating Sequential Processes) and BSP (Bulk Synchronous Parallelism). Formal semantics (through modelling in classical CSP), implementation details and early performance benchmarks (16 nanoseconds per process per barrier synchronisation on a 3.2 GHz Pentium IV) are presented, along with some likely directions for future research. Applications are outlined for the fine-grained modelling of dynamic systems, where barriers are used for maintaining simulation time and the phased execution of time steps, coordinating safe and desired patterns of communication between millions (and more) of processes. This work forms part of our TUNA project, investigating emergent properties in large dynamic systems (nanite assemblies).