Barrier Synchronisation for occam-pi

This paper introduces a safe language binding for CSP multiway events (barriers) that has been built into occampi (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). The occampi barriers are more general than those of BSP (an occampi system can contain any number of barriers, with some processes ignoring them and some registered with many). On the other hand, they are also, currently, less general than those of CSP (occampi processes must commit to barrier synchronisation -- it cannot be used as part of a choice or ALT). Structured support for resignation, a higher-level CSP design pattern, is also built into occampi barriers. Applications are outlined for fine-grained modelling of dynamic systems, where the barriers are used for maintaining simulation time and synchronising safe access to shared data between millions of processes. Implementation details and early performance benchmarks (16 nanoseconds per process per barrier synchronisation on a 3.2 GHz. Pentium IV) are also presented, along with some likely directions for future research.