Splitting Atoms with Rely/Guarantee Conditions Coupled with Data Reification

Jones, CB; Pierce, KG

doi:10.1007/978-3-540-87603-8_47

Splitting Atoms with Rely/Guarantee Conditions Coupled with Data Reification

Lookup NU author(s): Emeritus Professor Cliff Jones ORCiD, Dr Ken Pierce

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Abstract

This paper presents a novel formal development of a non-trivial parallel program: Simpson’s implementation of asynchronous communication mechanisms (ACMs). Although the correctness of the “4-slot algorithm” has been shown elsewhere, earlier developments are by no means intuitive. The aims of this paper include both the presentation of an understandable (yet formal) design history and the establishment of another way of “splitting (software) atoms”. Using the “fiction of atomicity” as an aid to understanding the initial steps of development, the top-level specification is developed to code. The rely-guarantee approach is, here, combined with notions of read/write frames and “phased” specifications; the atomicity assumptions implied by rely/guarantee conditions are realised by clever choice of data representation. The development method herein is compared with other approaches –in a spirit of cooperation– as the authors believe that constructive comparison elucidates many of the finer points in the “4-slot” specification/development and of parallel programs in general.