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

The symbiosis of concurrency and verification: teaching and case studies

Concurrency is beginning to be accepted as a core knowledge area in the undergraduate CS curriculum—no longer isolated, for example, as a support mechanism in a module on operating systems or reserved as an advanced discipline for later study. Formal verification of system properties is often considered a difficult subject area, requiring significant mathematical knowledge and generally restricted to smaller systems employing sequential logic only. This paper presents materials, methods and experiences of teaching concurrency and verification as a unified subject, as early as possible in the curriculum, so that they become fundamental elements of our software engineering tool kit—to be used together every day as a matter of course. Concurrency and verification should live in symbiosis. Verification is essential for concurrent systems as testing becomes especially inadequate in the face of complex non-deterministic (and, therefore, hard to repeat) behaviours. Concurrency should simplify the expression of most scales and forms of computer system by reflecting the concurrency of the worlds in which they operate (and, therefore, have to model); simplified expression leads to simplified reasoning and, hence, verification. Our approach lets these skills be developed without requiring students to be trained in the underlying formal mathematics. Instead, we build on the work of those who have engineered that necessary mathematics into the concurrency models we use (CSP, ?-calculus), the model checker (FDR) that lets us explore and verify those systems, and the programming languages/libraries (occam-?, Go, JCSP, ProcessJ) that let us design and build efficient executable systems within these models. This paper introduces a workflow methodology for the development and verification of concurrent systems; it also presents and reflects on two open-ended case studies, using this workflow, developed at the authors’ two universities. Concerns analysed include safety (don’t do bad things), liveness (do good things) and low probability deadlock (that testing fails to discover). The necessary technical background is given to make this paper self-contained and its work simple to reproduce and extend

Assessing the quality of audio and video components in desktop multimedia conferencing

This thesis seeks to address the HCI (Human-Computer Interaction) research problem of how to establish the level of audio and video quality that end users require to successfully perform tasks via networked desktop videoconferencing. There are currently no established HCI methods of assessing the perceived quality of audio and video delivered in desktop videoconferencing. The transport of real-time speech and video information across new digital networks causes novel and different degradations, problems and issues to those common in the traditional telecommunications areas (telephone and television). Traditional assessment methods involve the use of very short test samples, are traditionally conducted outside a task-based environment, and focus on whether a degradation is noticed or not. But these methods cannot help establish what audio-visual quality is required by users to perform tasks successfully with the minimum of user cost, in interactive conferencing environments. This thesis addresses this research gap by investigating and developing a battery of assessment methods for networked videoconferencing, suitable for use in both field trials and laboratory-based studies. The development and use of these new methods helps identify the most critical variables (and levels of these variables) that affect perceived quality, and means by which network designers and HCI practitioners can address these problems are suggested. The output of the thesis therefore contributes both methodological (i.e. new rating scales and data-gathering methods) and substantive (i.e. explicit knowledge about quality requirements for certain tasks) knowledge to the HCI and networking research communities on the subjective quality requirements of real-time interaction in networked videoconferencing environments. Exploratory research is carried out through an interleaved series of field trials and controlled studies, advancing substantive and methodological knowledge in an incremental fashion. Initial studies use the ITU-recommended assessment methods, but these are found to be unsuitable for assessing networked speech and video quality for a number of reasons. Therefore later studies investigate and establish a novel polar rating scale, which can be used both as a static rating scale and as a dynamic continuous slider. These and further developments of the methods in future lab- based and real conferencing environments will enable subjective quality requirements and guidelines for different videoconferencing tasks to be established

Dynamics and pragmatics for high performance concurrency

This thesis is concerned with support at all levels for building highly concurrent and dynamic parallel processing systems. The CSP model of concurrency, as (largely) embodied in the occam programming language is used due to its simplicity, expressiveness, architecture- independent nature, and potential for high performance. Additionally, occam provides guarantees regarding freedom from aliasing and race-hazard error. This thesis addresses one of the grand challenges of present day computer science: providing a software technology that offers the dynamic flexibility and performance of mainstream object oriented environments with the level of safety, formal analysis, modularity and lightweight concurrency offered by CSP/occam. Two approaches to this challenge are possible: do something to make the mainstream languages (e.g. Java, C++) safe, or make occam dynamic -- without compromising its existing good properties. This thesis follows the latter route. The first part of this thesis concentrates on enhancing the occam language and run-time system, on a commodity platform (IBM PC) running the freely available Linux operating system. After a brief introduction to the various components of the kroc occam system, additions and extensions to the occam programming language and supporting run-time system are examined. These provide a greater degree of programming flexibility in occam (for example, by adding support for dynamic allocation, mobile semantics and dynamic network construction), without compromising the safety of programs which use them. Benchmarks are reported that demonstrate significant improvements in performance (for example, channel communication in tens of nano-seconds). The second part concentrates on improving the level of interaction between occam programs and the OS environment. Providing easy access to sockets and networking, for example. This thesis concludes with a discussion of the work presented herein, with consideration given to parallels with object-oriented languages. Also described are details of ongoing and potential future research. The modified language grammar, details of new compiler generated code, and miscellany are provided in the appendices.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Dynamics and pragmatics for high performance concurrency

This thesis is concerned with support at all levels for building highly concurrent and dynamic parallel processing systems. The CSP model of concurrency, as (largely) embodied in the occam programming language is used due to its simplicity, expressiveness, architecture- independent nature, and potential for high performance. Additionally, occam provides guarantees regarding freedom from aliasing and race-hazard error. This thesis addresses one of the grand challenges of present day computer science: providing a software technology that offers the dynamic flexibility and performance of mainstream object oriented environments with the level of safety, formal analysis, modularity and lightweight concurrency offered by CSP/occam. Two approaches to this challenge are possible: do something to make the mainstream languages (e.g. Java, C++) safe, or make occam dynamic -- without compromising its existing good properties. This thesis follows the latter route. The first part of this thesis concentrates on enhancing the occam language and run-time system, on a commodity platform (IBM PC) running the freely available Linux operating system. After a brief introduction to the various components of the kroc occam system, additions and extensions to the occam programming language and supporting run-time system are examined. These provide a greater degree of programming flexibility in occam (for example, by adding support for dynamic allocation, mobile semantics and dynamic network construction), without compromising the safety of programs which use them. Benchmarks are reported that demonstrate significant improvements in performance (for example, channel communication in tens of nano-seconds). The second part concentrates on improving the level of interaction between occam programs and the OS environment. Providing easy access to sockets and networking, for example. This thesis concludes with a discussion of the work presented herein, with consideration given to parallels with object-oriented languages. Also described are details of ongoing and potential future research. The modified language grammar, details of new compiler generated code, and miscellany are provided in the appendices

Spatio-temporal modelling for issues in crime and security

The distribution of incidents in time and space is a central issue in the study of crime, for both theoretical and practical reasons. It is also a context in which quantitative analysis and modelling has significant potential value: such research represents a means by which the implications of theory can be examined rigorously, and can also provide tools which support both policing and policy-making. The nature of the field, however, presents a number of challenges, particularly with regard to the incorporation of complex environmental factors and the modelling of individual-level behaviour. In this thesis, the techniques of complexity science are used to overcome these issues, and the approach is demonstrated using a number of examples from a range of crime types. The thesis begins by presenting a network-based framework for the analysis of spatio-temporal clustering. It is demonstrated that signature `motifs' can be identified in patterns of offending for burglary and maritime piracy, and that the technique provides a more nuanced characterisation of clustering than existing approaches. Analysis is then presented of the relationship between street network structure and the distribution of urban crime. It is shown that burglary risk is predicted by the graph-theoretic properties of street segments; in particular, those which correspond to levels of street usage. It is further demonstrated that the `near-repeat' phenomenon in burglary displays a form of directionality, which can be reconciled with a novel street network metric. These results are then used to inform a mathematical model of burglary, which is situated on a network and which may be used for prediction. This model is analysed and its behaviour characterised in terms of urban form. Finally, a model is presented for a contrasting crime problem, the London riots of 2011, and used to examine a number of policy questions

High performance Cholesky and symmetric indefinite factorizations with applications

The process of factorizing a symmetric matrix using the Cholesky (LLT ) or indefinite (LDLT ) factorization of A allows the efficient solution of systems Ax = b when A is symmetric. This thesis describes the development of new serial and parallel techniques for this problem and demonstrates them in the setting of interior point methods. In serial, the effects of various scalings are reported, and a fast and robust mixed precision sparse solver is developed. In parallel, DAG-driven dense and sparse factorizations are developed for the positive definite case. These achieve performance comparable with other world-leading implementations using a novel algorithm in the same family as those given by Buttari et al. for the dense problem. Performance of these techniques in the context of an interior point method is assessed

Multi-resource approach to asynchronous SoC : design and tool support

As silicon cost reduces, the demands for higher performance and lower power consumption are ever increasing. The ability to dynamically control the number of resources employed can help balance and optimise a system in terms of its throughput, power consumption, and resilience to errors. The management of multiple resources requires building more advanced resource allocation logic than traditional 1-of-N arbiters posing the need for the efficient design flow supporting both the design and verification of such systems. Networks-on-Chip provide a good application example of distributed arbitration, in which the processor cores needing to transmit data are the clients; and the point-to-point links are the resources managed by routers. Building fast and smart arbiters can greatly benefit such systems in providing efficient and reliable communication service. In this thesis, a multi-resource arbiter was developed based on the Signal Transition Graph (STG) development flow. The arbiter distributes multiple active interchangeable resources that initiate requests when they are ready to be used. It supports concurrent resource utilization, which benefits creating asynchronous Multiple-Input-Multiple- Output (MIMO) queues. In order to deal with designs of higher complexity, an arbiter-oriented design flow is proposed. The flow is based on digital circuit components that are represented internally as STGs. This allows designing circuits without directly working with STGs but allowing their use for synthesis and formal verification. The interfaces for modelling, simulation, and visual model representation of the flow were implemented based on the existing modelling framework. As a result, the verification phase of the flow has helped to find hazards in existing Priority arbiter implementations. Finally, based on the logic-gate flow, the structure of a low-latency general purpose arbiter was developed. This design supports a wide variety of arbitration problems including the multi-resource management, which can benefit building NoCs employing complex and adaptive routing techniques.EThOS - Electronic Theses Online ServiceEPSRC grant GR/E044662/1 (STEP)GBUnited Kingdo