The Synchronous Approach to Reactive and Real-Time Systems

Abstract

This chapter discusses the major issues in the area of reactive and real-time programming, insisting particularly on safety constraints. It presents the new synchronous programming approach. Based on simple examples, it discuses two orthogonal synchronous styles and their semantics: a state-based style and a dataflow based style. Each style applies to a particular class of problems; complex applications will certainly require the cooperation of both. It is commonly accepted to call real-time a program or system that receives external interrupts or reads sensors connected to the physical world, and outputs commands to it. Real-time programming is an essential industrial activity whose importance keeps increasing. Factories, plants, transportation systems, cars, and a wide variety of everyday objects are or will be computer controlled. Safety is a crucial concern for reactive and real-time programs. In this area, a simple bug can have extreme consequences. Logical correctness is the respect of the input/output specification; it is essential in all cases. Temporal correctness is a further requirement of real-time applications: A logically correct real-time program can fail to adequately control its environment if its outputs are not produced on time.