Abstract. This paper presents a new model for mobile processes in occam-π. A process, embedded anywhere in a dynamically evolving network, may suspend itself mid-execution, be safely disconnected from its local environment, moved (by communication along a channel), reconnected to a new environment and reactivated. Upon reactivation, the process resumes execution from the same state (i.e. data values and code positions) it held when it suspended. Its view of its environment is unchanged, since that is abstracted by its synchronisation (e.g. channels and barriers) interface and that remains constant. The environment behind that interface will (usually) be completely different. The mobile process itself may contain any number of levels of dynamic sub-network. This model is simpler and, in some ways, more powerful than our earlier proposal, which required a process to terminate before it could be moved. Its formal semantics and implementation, however, throw up extra challenges. We present details and performance of an initial implementation.

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[1,2,3] as captured by the JCSP [4,5,6,7,8,9]

Abstract. We consider models of emergence, adding downward causation to conventional models where causation permeates from low-level elements to high-level behaviour. We describe an architecture and prototype simulation medium for tagging and modelling emergent features in CA-like systems. This is part of ongoing work on engineering emergence.

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.