Understanding Concurrent Systems

CSP notation has been used extensively for teaching and applying concurrency theory, ever since the publication of the text Communicating Sequential Processes by C.A.R. Hoare in 1985. Both a programming language and a specification language, the theory of CSP helps users to understand concurrent systems, and to decide whether a program meets its specification. As a member of the family of process algebras, the concepts of communication and interaction are presented in an algebraic style. An invaluable reference on the state of the art in CSP, Understanding Concurrent Systems also serves as a comprehensive introduction to the field, in addition to providing material for a number of more advanced courses. A first point of reference for anyone wanting to use CSP or learn about its theory, the book also introduces other views of concurrency, using CSP to model and explain these. The text is fully integrated with CSP-based tools such as FDR, and describes how to create new tools based on FDR. Most of the book relies on no theoretical background other than a basic knowledge of sets and sequences. Sophisticated mathematical arguments are avoided whenever possible. Topics and features: presents a comprehensive introduction to CSP; discusses the latest advances in CSP, covering topics of operational semantics, denotational models, finite observation models and infinite-behaviour models, and algebraic semantics; explores the practical application of CSP, including timed modelling, discrete modelling, parameterised verifications and the state explosion problem, and advanced topics in the use of FDR; examines the ability of CSP to describe and enable reasoning about parallel systems modelled in other paradigms; covers a broad variety of concurrent systems, including combinatorial, timed, priority-based, mobile, shared variable, statecharts, buffered and asynchronous systems; contains exercises and case studies to support the text; supplies further tools and information at the associated website: http://www.comlab.ox.ac.uk/ucs/. From undergraduate students of computer science in need of an introduction to the area, to researchers and practitioners desiring a more in-depth understanding of theory and practice of concurrent systems, this broad-ranging text/reference is essential reading for anyone interested in Hoare’s CSP.

Concurrent systems abound in human experience but their fully adequate conceptualization as yet eludes our most able thinkers. The COSY (ConcurrentSystem) notation and theory was developed in the last decade as one of a number of mathematical approaches for conceptualizing and analyzing concurrent and reactive systems. The COSY approach extends theconventional notions of grammar and automaton from formal language and automata theory to collections of "synchronized" grammars and automata, permitting system specification and analysis of "true" concurrency without reduction to non-determinism. COSY theory is developed to a great level of detail and constitutes the first uniform and self-contained presentationof all results about COSY published in the past, as well as including many new results. COSY theory is used to analyze a sufficient number of typical problems involving concurrency, synchronization and scheduling, to allow the reader to apply the techniques presented tosimilar problems. The COSY model is also related to many alternative models of concurrency, particularly Petri Nets, Communicating Sequential Processes and the Calculus of Communicating Systems.

The cooperation test [Apt, Francez & de Roever] was originally conceived to capture the proof theoretical analogue of distributed message exchange between disjoint processes, as opposed to the interference freedom test [Owicki & Gries], being the proof theoretical analogue of concurrent communication by means of interference through jointly shared variables. Some authors ([Levin & Gries, Lamport & Schneider, Schlichting and Schneider]) stress that both forms of communication can be proof theoretically characterized using interference freedom only, since proofs for both ultimately amount to an invariance proof of a big global assertion [Ashcroft], invariance of whose parts amounts to interference freedom. Yet I feel that the characteristic nature of the cooperation test is still preserved in the analysis of these authors, because in their analysis of CSP the part dealing with interference freedom specializes to maintenance of a global invariant, the expression of which requires per process the introduction of auxiliary variables which are updated in that process only, thus preserving the concept of disjointness (as opposed to sharing), since now all variables from different processes are disjoint. The cooperation test has been applied to characterize concurrent communication as occurring in Hoare's Communicating Sequential Processes (CSP) [Hoare 2], Ichbiah's ADA [ARM], and Brinch Hansen's Distributed Processes (DP) [Brinch Hansen]. This characterization has been certified through soundness and completeness proofs [Apt 2, Gerth]. As in the interference freedom test this characterization consists of two stages, a local sequential stage and a global stage.

Since Professor Hoare's book Communicating Sequential Processes was first published, his notation has been extensively used for teaching and applying concurrency theory. The most significant development since then has been the emergence of tools to support the teaching and industrial application of CSP. This has turned CSP from a notation used mainly for toy examples into one which can and does support the description of industrial-sized problems. In order to understand the tools you need a good grasp of the fundamental concepts of CSP, therefore the book is, in the first instance, a text on the principles of the language rather than being a manual on how to apply its tools. The Theory and Practice of Concurrency is divided into 3 sections. Part I is a foundation course on CSP, covering essentially the same material as the Hoare book, except that most of the mathematical theory has been omitted. It introduces the ideas behind the operational, denotational and algebraic models of CSP. Parts II and III go into more detail about the theory and practice of CSP. Either of them would make a one semester course or though they are independent of each other. This book assumes no mathematical knowledge except for a basic understanding of sets, sequences and functions. Part I and III use no sophisticated mathematics, and the extra amount needed for Part II is contained within Appendix A (which introduces the theory of partial order and metric/restriction spaces). The book brings substantial new insights into the important subjects of computer security, fault tolerance, real-time modelling, communications protocols and distributed databases. Each of these is supported by a case study and guidance on how to apply automated analysis to verify systems.

This volume contains papers presented at the BCS-FACS Workshop on Specification and Verification of Concurrent Systems held on 6-8 July 1988, at the University of Stirling, Scotland. Specification and verification techniques are playing an increasingly important role in the design and production of practical concurrent systems. The wider application of these techniques serves to identify difficult problems that require new approaches to their solution and further developments in specification and verification. The Workshop aimed to capture this interplay by providing a forum for the exchange of the experience of academic and industrial experts in the field. Presentations included: surveys, original research, practical experi ence with methods, tools and environments in the following or related areas: Object-oriented, process, data and logic based models and specifi cation methods for concurrent systems Verification of concurrent systems Tools and environments for the analysis of concurrent systems Applications of specification languages to practical concurrent system design and development. We should like to thank the invited speakers and all the authors of the papers whose work contributed to making the Workshop such a success. We were particularly pleased with the international response to our call for papers. Invited Speakers Pierre America Philips Research Laboratories University of Warwick Professor M. Joseph David Freestone British Telecom Organising Committee Charles Rattray Dr Muffy Thomas Dr Simon Jones Dr John Cooke Professor Ken Turner Derek Coleman Maurice Naftalin Dr Peter Scharbach vi Preface We would like to aeknowledge the finaneial eontribution made by SD-Sysems Designers pie, Camberley, Surrey.

The control-flow issues presented in this textbook are extremely relevant in modern computer languages and programming styles. In addition to the basic control-flow mechanisms, virtually all new computer languages provide some form of exceptional control flow to support robust programming introduced in this textbook. Also, concurrency capabilities are appearing with increasing frequency in both new and old programming languages, and are covered in this book. Understanding Control Flow: With Concurrent Programming Using μC++ starts with looping, and works through each of the basic control-flow concepts, examining why each is fundamental and where it is useful. Time is spent on each concept according to its level of difficulty. Examples and exercises are also provided in this textbook. New programming methodologies are requiring new forms of control flow, and new programming languages are supporting these methodologies with new control structures, such as the concurrency constructs discussed in this textbook. Most computers now contain multi-threading and multi-cores, while multiple processors and distributed systems are ubiquitous — all of which require advanced programming methodologies to take full advantage of the available parallelism summarized in this textbook. Advance forms of control flow are becoming basic programming skills needed by all programmers, not just graduate students working in the operating systems or database disciplines. This textbook is designed for advanced-level students studying computer science and engineering. Professionals and researchers working in this field, specifically programming and software engineering, will find this book useful as a reference.

The CSP approach has been widely used in the specification, analysis and verification of concurrent and real-time systems, and for understanding the particular issues that can arise when concurrency is present. It provides a language which enables specifications and designs to be clearly expressed and understood, together with a supporting theory which allows them to be analyzed and shown to be correct. This book supports advanced level courses on concurrency covering timed and untimed CSP. The first half introduces the language of CSP, the primary semantic models (traces, failures, divergences and infinite traces), and their use in the modelling, analysis and verification of concurrent systems. The second half of the book introduces time into the language, brings in the timed semantic model (timed failures) and finally presents the theory of timewise refinement which links the two halves together. Accompanying website: http://www.cs.rhbnc.ac.uk/books/concurrency Containing the following: -Exercises and solutions -Instructors resources - Example CSP programs to run on FDR and ProBe -Links to useful sites Partial Contents: Part I: The Language of CSP; Sequential Processes; Concurrency; Abstraction and Control Flow; Part II: Analyzing Processes; Traces; Specification and Verification with Traces; Stable Failures; Specification and Verification with Failures; Failures, Divergences, and Infinite Traces; Part III: Introducing Time; The Timed Language; Timed transition systems; Part IV: Timed Analysis; Semantics of Timed CSP; Timed Specification and Verification; Timewise Refinement; Appendix A: Event-based Time; A.1 Standard CSP and $tock$; A.2 Translating from Timed CSP; A.3 Notes; Appendix B: Model-checking with FDR; B.1 Interacting with FDR; B.2 How FDR Checks Refinement; B.3 Machine readable CSP; Index of Processes.

A text intended as a modern replacement for a first course in operating systems modern in the sense that concurrency is a central focus throughout; distributed systems are treated as the norm rather than single-processor systems, and effective links are provided to other systems courses. It is also