SUMMARYA fine-grained massively parallel and process-oriented architecture for the modelling of complex systems is presented. We propose that the concurrency in the model simplifies its design and construction by directly reflecting the processes in the natural world. The architecture is based on CSP, extended with mechanisms for process mobility from the pi-calculus; implementations are presented using the occam-pi language. A case study, modelling platelets (possibly artificial) within a blood vessel, is described. The aim for this model is to engineer emergent behaviour: the clotting of platelets in response to a wound in the blood vessel wall and the staunching of blood loss. A three-dimensional model is constructed, along with mechanisms for visualization and interaction. Its expressiveness and efficiency relies strongly on the dynamic and mobile capabilities of occam-pi. General principles for the design of large and complex system models are drawn. The described case study runs to millions of processes engaged in ever-changing communication topologies. It is free from deadlock, livelock, race hazards and starvation by design, employing a small set of synchronization patterns for which we have proven safety theorems. Compiled occam-p codes automatically and efficiently exploit all cores in a shared-memory multiprocessor system. They are also straightforward to distribute over standard cluster architectures.

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Intel's latest processor microarchitecture, Haswell, adds support for a restricted form of transactional memory to the x86 programming model. We explore how this can be applied to three garbage collection scenarios in Jikes RVM: parallel copying, concurrent copying and bitmap marking. We demonstrate gains in concurrent copying speed over traditional synchronisation mechanisms of 48-101%. We also show how similar but portable performance gains can be achieved through software transactional memory techniques. We identify the architectural overhead of capturing sufficient work for transactional execution as a major stumbling block to the effective use of transactions in the other scenarios.

Process orientation is an approach to concurrency that uses concepts of processes and message-passing communication, with whole systems constructed from layered and dynamically evolving networks of communicating processes. The work described in this paper relates to the automatic model generation and verification of systems developed in processoriented languages. We discuss some early applications of this technique to our experimental operating system, RMoX, as a means to giving a guarantee of correct system behaviour at a range of levels.

Abstract. Process-oriented programming is a design methodology in which software applications are constructed from communicating concurrent processes. A process-oriented design is typically composed of a large number of small isolated concurrent components. These components allow for the scalable parallel execution of the resulting application on both shared-memory and distributed-memory architectures. In this paper we present a runtime designed to support process-oriented programming by providing lightweight processes and communication primitives. Our runtime scheduler, implemented using lock-free algorithms, automatically executes concurrent components in parallel on multicore systems. Runtime heuristics dynamically group processes into cache-affine work units based on communication patterns. Work units are then distributed via wait-free work-stealing. Initial performance analysis shows that, using the algorithms presented in this paper, process-oriented software can execute with an efficiency approaching that of optimised sequential and coarse-grain threaded designs.