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

Specifying and reasoning about concurrent systems in logic

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Continuous-time temporal logic specification and verification for nonlinear biological systems in uncertain contexts

In this thesis we introduce a complete framework for modelling and verification of biological systems in uncertain contexts based on the bond-calculus process algebra and the LBUC spatio-temporal logic. The bond-calculus is a biological process algebra which captures complex patterns of interaction based on affinity patterns, a novel communication mechanism using pattern matching to express multiway interaction affinities and general kinetic laws, whilst retaining an agent-centric modelling style for biomolecular species. The bond-calculus is equipped with a novel continuous semantics which maps models to systems of Ordinary Differential Equations (ODEs) in a compositional way. We then extend the bond-calculus to handle uncertain models, featuring interval uncertainties in their species concentrations and reaction rate parameters. Our semantics is also extended to handle uncertainty in every aspect of a model, producing non-deterministic continuous systems whose behaviour depends either on time-independent uncertain parameters and initial conditions, corresponding to our partial knowledge of the system at hand, or time-varying uncertain inputs, corresponding to genuine variability in a system’s behaviour based on environmental factors. This language is then coupled with the LBUC spatio-temporal logic which combines Signal Temporal Logic (STL) temporal operators with an uncertain context operator which quantifies over an uncertain context model describing the range of environments over which a property must hold. We develop model-checking procedures for STL and LBUC properties based on verified signal monitoring over flowpipes produced by the Flow* verified integrator, including the technique of masking which directs monitoring for atomic propositions to time regions relevant to the overall verification problem at hand. This allows us to monitor many interesting nested contextual properties and frequently reduces monitoring costs by an order of magnitude. Finally, we explore the technique of contextual signal monitoring which can use a single Flow* flowpipe representing a functional dependency to complete a whole tree of signals corresponding to different uncertain contexts. This allows us to produce refined monitoring results over the whole space and to explore the variation in system behaviour in different contexts

Revisiting sequential composition in process calculi

International audienceThe article reviews the various ways sequential composition is defined in traditional process calculi, and shows that such definitions are not optimal, thus limiting the dissemination of concurrency theory ideas among computer scientists. An alternative approach is proposed, based on a symmetric binary operator and write-many variables. This approach, which generalizes traditional process calculi, has been used to define the new LNT language implemented in the CADP toolbox. Feedback gained from university lectures and real-life case studies shows a high acceptance by computer-science students and industry engineers

Programming Languages and Systems

This open access book constitutes the proceedings of the 31st European Symposium on Programming, ESOP 2022, which was held during April 5-7, 2022, in Munich, Germany, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2022. The 21 regular papers presented in this volume were carefully reviewed and selected from 64 submissions. They deal with fundamental issues in the specification, design, analysis, and implementation of programming languages and systems