arXiv subjects

Cliff B. Jones

Publications and source records attributed to Cliff B. Jones.

7 recordsLinked to original sources

arXiv2025

Reasoning about concurrent loops and recursion with rely-guarantee rules

The objective of this paper is to present general, mechanically verified, refinement rules for reasoning about recursive programs and while loops in the context of concurrency. We make use of the rely-guarantee approach to concurrency that facilitates reasoning about interference from concurrent threads in a compositional manner. Recursive programs can be defined as fixed points over a lattice of commands and hence we develop laws for reasoning about fixed points. Loops can be defined in terms of fixed points and hence the laws for recursion can be applied to develop laws for loops. Unlike many approaches to concurrency, we do not assume that expression evaluation is atomic.

cs.LO↗

arXiv2025

Reasoning about expression evaluation under interference

Hoare-style inference rules for program constructs permit the copying of expressions and tests from program text into logical contexts. It is known that this requires care even for sequential programs but much more serious issues arise with concurrent programs because of potential interference to the values of variables. The "rely-guarantee" approach tackles the challenge of recording acceptable interference and offers a way to provide safe inference rules for concurrent constructs. This paper shows how the algebraic presentation of rely-guarantee ideas can clarify and formalise the conditions for safely re-using expressions and tests from program text in logical contexts for reasoning about concurrent programs; crucially this extends to handling expressions that reference more than one shared variable. A non-trivial example related to the Fischer-Galler forest representation of equivalence relations is treated.

cs.LO↗

arXiv2024

Using Rely/Guarantee to Pinpoint Assumptions underlying Security Protocols

The verification of security protocols is essential, in order to ensure the absence of potential attacks. However, verification results are only valid with respect to the assumptions under which the verification was performed. These assumptions are often hidden and are difficult to identify, making it unclear whether a given protocol is safe to deploy into a particular environment. Rely/guarantee provides a mechanism for abstractly reasoning about the interference from the environment. Using this approach, the assumptions are made clear and precise. This paper investigates this approach on the Needham-Schroeder Public Key protocol, showing that the technique can effectively uncover the assumptions under which the protocol can withstand attacks from intruders.

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arXiv2024

Data reification in a concurrent rely-guarantee algebra

Specifications of significant systems can be made short and perspicuous by using abstract data types; data reification can provide a clear, stepwise, development history of programs that use more efficient concrete representations. Data reification (or "refinement") techniques for sequential programs are well established. This paper applies these ideas to concurrency, in particular, an algebraic theory supporting rely-guarantee reasoning about concurrency. A concurrent version of the Galler-Fischer equivalence relation data structure is used as an example.

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arXiv2023

Extending Rely-Guarantee thinking to handle Real-Time Scheduling

The reference point for developing any artefact is its specification; to develop software formally, a formal specification is required. For sequential programs, pre and post conditions (together with abstract objects) suffice; rely and guarantee conditions extend the scope of formal development approaches to tackle concurrency. In addition, real-time systems need ways of both requiring progress and relating that progress to some notion of time. This paper extends rely-guarantee ideas to cope with specifications of -- and assumptions about -- real-time schedulers. Furthermore it shows how the approach helps identify and specify fault-tolerance aspects of such schedulers by systematically challenging the assumptions.

cs.SE↗

arXiv2021

The development and deployment of formal methods in the UK

UK researchers have made major contributions to the technical ideas underpinning formal approaches to the specification and development of computer systems. Perhaps as a consequence of this, some of the significant attempts to deploy theoretical ideas into practical environments have taken place in the UK. The authors of this paper have been involved in formal methods for many years and both have tracked a significant proportion of the whole story. This paper both lists key ideas and indicates where attempts were made to use the ideas in practice. Not all of these deployment stories have been a complete success and an attempt is made to tease out lessons that influence the probability of long-term impact.

cs.SE↗

arXiv2016

Possible values: exploring a concept for concurrency

An important issue in concurrency is interference. This issue manifests itself in both shared-variable and communication-based concurrency --- this paper focusses on the former case where interference is caused by the environment of a process changing the values of shared variables. Rely/guarantee approaches have been shown to be useful in specifying and reasoning compositionally about concurrent programs. This paper explores the use of a "possible values" notation for reasoning about variables whose values can be changed multiple times by interference. Apart from the value of this concept in providing clear specifications, it offers a principled way of avoiding the need for some auxiliary (or ghost) variables whose unwise use can destroy compositionality.

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