A Process-Oriented Architecture for Complex System Modelling

A fine-grained massively-parallel process-oriented model of platelets (potentially artificial) within a blood vessel is presented. This is a CSP inspired design, expressed and implemented using the occam-pi language. It is part of the TUNA pilot study on nanite assemblers at the universities of York, Surrey and Kent. The aim for this model is to engineer emergent behaviour from the platelets, such that they respond to a wound in the blood vessel wall in a way similar to that found in the human body -- i.e. the formation of clots to stem blood flow from the wound and facilitate healing. An architecture for a three dimensional model (relying strongly on the dynamic and mobile capabilities of occam-pi) is given, along with mechanisms for visualisation and interaction. The biological accuracy of the current model is very approximate. However, its process-oriented nature enables simple refinement (through the addition of processes modelling different stimulants/inhibitors of the clotting reaction, different platelet types and other participating organelles) to greater and greater realism. Even with the current system, simple experiments are possible and have scientific interest (e.g. the effect of platelet density on the success of the clotting mechanism in stemming blood flow: too high or too low and the process fails). 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 em by design, employing a small set of synchronisation patterns for which we have proven safety theorems

An evaluation of Intel’s Restricted Transactional Memory for CPAs,

Abstract. With the release of their latest processor microarchitecture, codenamed Haswell, Intel added new Transactional Synchronization Extensions (TSX) to their processors' instruction set. These extensions include support for Restricted Transactional Memory (RTM), a programming model in which arbitrary sized units of memory can be read and written in an atomic manner. This paper describes the low-level RTM programming model, benchmarks the performance of its instructions and speculates on how it may be used to implement and enhance Communicating Process Architectures

Transactional Sapphire: Lessons in High Performance, On-the-fly Garbage Collection

Constructing a high-performance garbage collector is hard. Constructing a fully concurrent 'on-the-fly', compacting collector is much more so. We describe our experience of implementing the Sapphire algorithm as the first on-the-fly, parallel, replication copying, garbage collector for the Jikes RVM Java virtual machine. In part, we explain our innovations such as copying with hardware and software transactions, on-the-fly management of Java's reference types and simple, yet correct, lock-free management of volatile fields in a replicating collector. We fully evaluate, for the first time, and using realistic benchmarks, Sapphire's performance and suitability as a low latency collector. An important contribution of this work is a detailed description of our experience of building an on-the-fly copying collector for a complete JVM with some assurance that it is correct. A key aspect of this is model checking of critical components of this complicated and highly concurrent system

Virtual Machine Based Debugging for occam-pi

While we strive to create robust language constructs and design patterns which prevent the introduction of faults during software development, an inevitable element of human error still remains. We must therefore endeavor to ease and accelerate the process of diagnosing and fixing software faults, commonly known as 'debugging'. Current support for debugging occam-pi programs is fairly limited. At best the developer is presented with a reference to the last known code line executed before their program abnormally terminated. This assumes the program does in fact terminate, and does not instead live-lock. In cases where this support is not sufficient, developers must instrument their own tracing support, ``printf style''. An exercise which typically enlightens one as to the true meaning of concurrency... In this paper we explore previous work in the field of debugging occam programs and introduce a new method for run-time monitoring of occam-pi applications, based on the Transterpreter virtual machine interpreter. By adding a set of extensions to the Transterpreter, we give occam-pi processes the ability to interact with their execution environment. Use of a virtual machine allows us to expose program execution state which would otherwise require non-portable or specialised hardware support. Using a model which bears similarities to that applied when debugging embedded systems with a JTAG connection, we describe debugging occam-pi by mediating the execution of one execution process from another

A Process Oriented Approach to USB Driver Development

Operating-systems are the core software component of many modern computer systems, ranging from small specialised embedded systems through to large distributed operating-systems. The demands placed upon these systems are increasingly complex, in particular the need to handle concurrency: to exploit increasingly parallel (multicore) hardware; support increasing numbers of user and system processes; and to take advantage of increasingly distributed and decentralised systems. The languages and designs that existing operating-systems employ provide little support for concurrency, leading to unmanageable programming complexities and ultimately errors in the resulting systems; hard to detect, hard to remove, and almost impossible to prove correct. Implemented in occam-pi, a CSP derived language that provides guarantees of freedom from race-hazards and aliasing error, the RMoX operating-system represents a novel approach to operating-systems, utilising concurrency at all levels to simplify design and implementation. This paper presents the USB (universal serial bus) devicedriver infrastructure used in the RMoX system, demonstrating that a highly concurrent process-orientated approach to device-driver design and implementation is feasible, efficient and results in systems that are reliable, secure and scalable

An Evaluation of Intel's Restricted Transactional Memory for CPAs

With the release of their latest processor microarchitecture, codenamed Haswell, Intel added new Transactional Synchronization Extensions (TSX) to their processors' instruction set. These extensions include support for Restricted Transactional Memory (RTM), a programming model in which arbitrary sized units of memory can be read and written in an atomic manner. This paper describes the low-level RTM programming model, benchmarks the performance of its instructions and speculates on how it may be used to implement and enhance Communicating Process Architectures

Exploring Garbage Collection with Haswell Hardware Transactional Memory

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

Video Processing in occam-pi

The occam-pi language provides many novel features for concurrent software development. This paper describes a video processing framework that explores the use of these features for multimedia applications. Processes are used to encapsulate operations on video and audio streams; mobile data types are used to transfer data between them efficiently, and mobile channels allow the process network to be dynamically reconfigured at runtime. We present demonstration applications including an interactive video player. Preliminary benchmarks show that the framework has comparable overhead to multimedia systems programmed using traditional methods

Safe parallelism for robotic control

During the Spring 2008 semester at Olin College, we introduced the programming language occam-pi to undergraduates as part of their first course in robotics. Students were able to explore image processing and autonomous behavioral control in a parallel programming language on a small mobile robotics platform with just two weeks of tutorial instruction. Our experiences to date suggest that the language and tools we have developed allow the concise expression of complex robotic control systems, and enable the integration of events from the environment in a consistent and safe model for parallel control that is directly expressed in software