Ada-concurrency specified by graph grammars

Abstract

This paper demonstrates a notion for formal semantics specification of concurrent programming languages and applies it to the concurrent part of the programming language Ada. The abstract syntax of an Ada program is given by a graph representation called the program graph. This program graph is the input for an abstract interpreter consisting of a set of graph rewriting rules. Therefore, this interpreter is a graph rewriting system, i. e. a graph grammar. A derivation step in this graph grammar allows the parallel application of a finite set of sequential rewriting rules, thus modelling the independent progress of parallel tasks. It is shown that the notion successfully copes with Ada concurrency, including dynamic creation of tasks, task hierarchies, synchronization, and timing considerations. The abstract implementation by an interpreter gives rise to some considerations concerning the precision of the informal, official Ada Standard and the adequacy of some language features, especially with respect to the interaction of exception handling and concurrency.

This paper gives an extended abstract of the main ideas of [SPEC].