THE ESTEREL SYNCHRONOUS PROGRAMMING LANGUAGE - DESIGN, SEMANTICS, IMPLEMENTATION

We present the ESTEREL programming language which is especially designed to program reactive systems, that is systems which maintain a permanent interaction with their environment: real-time process controllers, communication protocols, man machine interface drivers, etc. ESTEREL is a deterministic concurrent programming language. It differs from classical asynchronous languages by its synchrony hypothesis: the outputs of a system are conceptually synchronous with its inputs. The synchrony hypothesis permits a high-level modular programming style simpler and more rigorous than its asynchronous counterpart. We present the imperative primitives of ESTEREL and the temporal manipulations they permit. We give a small programming example. We present two mathematical semantics of ESTEREL, which are given by conditional rewrite rules and related by a correctness theorem. The behavioral semantics defines the behavior of programs in an uneffective way as the solution of fixpoint equations. The effective execution semantics computes actions to be performed by a conceptually infinitely fast execution machine. To relate the two semantics, we solve the causality problems that are inherent in synchronous formalisms. We show how the ESTEREL v2 and ESTEREL v3 compilers efficiently translate concurrent ESTEREL programs into efficient equivalent sequential automata that can be implemented in conventional sequential languages. We discuss the quality of this object code and the practical adequacy of the synchrony hypothesis.