Reactive C: An extension of C to program reactive systems

Reactive systems are interactive programs that react continuously to sequences of activations coming from the external world. Reactive programming leads to a new programming style where one programs in terms of reactions to activations and reasons in a logic of instants. This paper describes an extension of the C programming language called RC (for ‘Reactive C’) to program reactive systems. The language RC is described, then some programming examples are given to illustrate the reactive approach. The main RC notions come directly from the Esterel synchronous programming language. Finally, the Esterel and RC languages are compared.     

The Synchronous Approach to Designing Reactive Systems

Synchronous programming is available through several formally defined languages having very different characteristics: Esterel is imperative, while Lustre and Signal are declarative in style; Statecharts and Argos are graphical languages that allow one to program by constructing hierarchical automata. Our motivation for taking the synchronous design paradigm further, integrating imperative, declarative (or dataflow), and graphical programming styles, is that real systems typically have components that match each of these profiles. This paper motivates our interest in the mixed language programming of embedded software around a number of examples, and sketches the semantical foundation of the Synchronie toolset which ensures a coherent computational model. This toolset supports a design trajectory that incorporates rapid prototyping and systematic testing for early design validation, an object oriented development methodology for long term software management, and formal verification at the level of automatically generated object code.     

Design of a Mobile Robot Controller using Esterel Tools

Robot controllers are often programmed using either standard sequential programming languages or a robot-specific language, which are then compiled to assembly language specific to the robot. Modern real-time programming languages, on the other hand, are more appropriate to program robots, as they better fit the real-time reactive model of robots. This paper reports on a project to program a non-trivial robot, the Rug Warrior, in the Artificial Intelligence Laboratory of UNSW, using Esterel, which is a real-time programming language. The approach is illustrated by simulation of a colony of Siberian ants using a group of Rug Warriors.     

Keeping calm in the face of change

Functional Reactive Programming (FRP) is an approach to reactive programming where systems are structured as networks of functions operating on signals (time-varying values). FRP is based on the synchronous data-flow paradigm and supports both (an approximation to) continuous-time and discrete-time signals (hybrid systems). What sets FRP apart from most other languages for similar applications is its support for systems with dynamic structure and for higher-order reactive constructs.     

Performance debugging of Esterel specifications

Synchronous languages like Esterel have been widely adopted for designing reactive systems in safety-critical domains such as avionics. Specifications written in Esterel are based on the underlying ??synchrony hypothesis??, which needs to be validated when Esterel specifications get compiled to real implementations (such as C code). In this work, we present a model-driven and architecture-aware timing analysis framework for C code generated from Esterel and executed on general-purpose processors. By integrating model-level information into the traditional timing analysis, we can efficiently compute accurate time estimates via systematically eliminating a large number of infeasible paths in the generated code. Experimental results show that with our proposed intermediate representation level infeasible path analysis in the model compilation, we obtain up to 16.1?% tighter WCET estimates compared to the traditional assembly code level infeasible path detection with substantially less analysis time. Furthermore, by maintaining the traceability links between Esterel specifications and the generated C code, we are able to map the time-critical computations at the C-level back to the Esterel-level.     

Type-safe casting

Many modern extensible systems, such as Java and the SPIN operating system, depend on type safety for memory protection. Unfortunately, current type-safe languages do not support systems programming well, because they do not give programmers the ability to deal with untyped data easily. In particular, they do not support the ability to cast between untyped data and language-level types. We describe a powerful, type-safe cast operator that helps programmers write low-level systems codes in type-safe languages. We have implemented this operator in Modula-3 for the SPIN operating system, and we give specific examples of how we use it in SPIN. © 1998 John Wiley & Sons, Ltd.     

SystemJ: A GALS language for system level design

In this paper we present the syntax, semantics, and compilation of a new system-level programming language called SystemJ. SystemJ is a multiclock language supporting the Globally Asynchronous Locally Synchronous (GALS) model of computation. The synchronous reactive (SR) model is used for synchronous parts of the modelled system, and those parts, which represent individual clock-domains, are coupled asynchronously each to the other on the top-level of system design. SystemJ is based on Java language, which is used to describe “instantaneous” data transformations. Hence, SystemJ is well suited for both software-based embedded and distributed systems. SystemJ offers effective modelling of (1) data transformations through the power of Java, (2) control and synchronous concurrency through the SR paradigm and (3) asynchronous concurrency through clock domains and rendezvous. The language is based on semantics that is amenable to efficient code generation and partial automatic verification. The SystemJ micro-step semantics provide asynchronous and synchronous extensions over the semantics of other SR languages such as Esterel and provide an ideal platform for efficient software implementation.     

Parallel developments in programming languages and operating systems

Three stages of the development of programming languages are examined and compared with similar stages in the development of operating systems. It is noted that not only do these stages agree but particular developments within these stages also have remarkable similarities; some of these are superficial while others are deeper. The parallels are used to note that certain developments have yet to occur in operating systems. Finally, the essential identity of purpose of programming languages and operating systems is discussed.     

Debugging mixed‐environment programs with Blink

Programmers build large‐scale systems with multiple languages to leverage legacy code and languages best suited to their problems. For instance, the same program may use Java for ease of programming and C to interface with the operating system. These programs pose significant debugging challenges, because programmers need to understand and control code across languages, which often execute in different environments. Unfortunately, traditional multilingual debuggers require a single execution environment. This paper presents a novel composition approach to building portable mixed‐environment debuggers, in which an intermediate agent interposes on language transitions, controlling and reusing single‐environment debuggers. We implement debugger composition in Blink, a debugger for Java, C, and the Jeannie programming language. We show that Blink is (i) simple: it requires modest amounts of new code; (ii) portable: it supports multiple Java virtual machines, C compilers, operating systems, and component debuggers; and (iii) powerful: composition eases debugging, while supporting new mixed‐language expression evaluation and Java native interface bug diagnostics. To demonstrate the generality of interposition, we build prototypes and demonstrate debugger language transitions with C for five of six other languages (Caml, Common Lisp, C#, Perl 5, Python, and Ruby) without modifications to their debuggers. Using real‐world case studies, we show that diagnosing language interface errors require prior single‐environment debuggers to restart execution multiple times, whereas Blink directly diagnoses them with one execution. Copyright © 2014 John Wiley & Sons, Ltd.     

ESUIF: An Open Esterel Compiler

I describe a new compiler infrastructure for imperative synchronous languages such as Esterel and E↕. Built on the S〉{ 2 system, it includes a new intermediate representation for this class of languages that has simple semantics designed for easy implementation in hardware or software. I describe the structure of this new compiler, the intermediate representation, and how Esterel source is translated into this intermediate representation.     

A formal approach to reactive systems software: A telecommunications application in Esterel

Esterel is a formally-defined language designed for programming reactive systems; namely, those that maintain a permanent interaction with their environment. The AT&T 5ESS^® telephone switching system is an example of a reactive system. We describe an implementation in Esterel of one feature of a 5ESS switch; this implementation has been tested in the 5ESS switch simulator. Furthermore, it has been formally verified that this implementation satisfies some safety properties stated by 5ESS software development. Our experience indicates that Esterel is suitable for programming industrial-strength reactive systems, and affords significant advantages in software development over more traditional programming languages used in industrial settings.An earlier version of this paper appeared in the Proceedings of the Workshop on Industrial-Strength Formal Specification Techniques, Boca Raton, Florida, 1995.The author is currently supported by a Fulbright fellowship from Spain's Ministry of Science and Education. The work described here was performed while the author was visiting AT&T Bell Laboratories.     

Success and failure analysis of a problem solving system implementation

The NAPSS (Numerical Analysis Problem Solving System) project was an attempt to develop an interactive system, with a high-level language resembling conventional mathematics, for solving problems in numerical analysis. This report uses NAPSS as an example to discuss some aspects of the design and implementation of the programming languages and software which comprise problem solving systems. Successful features as well as failures (with alternative proposals) are detailed in the areas of general language management, specific language features and the operating system interface. In general, a massive, coherent implementation of theoretical work being done at the frontiers of research has abundant opportunity for failure.     

A viable system structure for large‐scale software systems

A homogeneous system structure is proposed that enhances modularity and flexibility, and facilitates (further) development of large‐scale software systems in a major‐industry environment. In our opinion, it is an effective means of countering the inherent increase in software entropy when (further) developing existing large‐scale software systems, thereby substantially cutting down production costs. It can be applied generally both to new and existing systems, whether application programs or operating systems, promotes the parallel use of different programming paradigms and various implementation languages, and offers the option of either redesigning parts or introducing additional parts in stages based on a more modern technology. The proposed system structure is compared and contrasted with other architectures such as CORBA, and it is shown that it may be regarded as an embellishment of the CORBA architecture for the internal structuring or restructuring of possibly distributed software systems. So far it has been used in four releases of the BS2000/OSD operating system with very positive results. Dependencies between various entities – which we call ‘subsystems’ – in the course of the (further) development process, as well as during dynamic execution are minimized and well‐regulated. The subsystems may be loaded on demand during the session by a system authority. Every interface in the system is classified according to its permitted scope of use. For interfaces between subsystems, a uniform and standardized technique is introduced which uses the same format for all implementation languages at both the source‐ and binary‐code level. This technique exceeds the regulations in other architectures but actually achieves considerable rationalization. Copyright © 1999 John Wiley & Sons, Ltd.     

A Longitudinal Study of the Impact of Open Source Software Project Characteristics on Positive Outcomes

This article formulates and tests a set of hypotheses about the success of open source software projects with respect to market penetration and human resource attraction. The authors collected data from 1025 open source software projects in a longitudinal study. The cross-sectional results show that the extent of a project’s operating systems, the range of translated languages, programming languages, and project age positively impact OSS projects’ positive outcomes with respect to market penetration and human resource attraction.     

The implementation of concurrency for a PL/I-like language

The formulation of concurrency and synchronization has been recognized as a matter of growing importance in system programming languages in order to achieve well-structured, reliable and easy to understand system software such as operating systems. Unfortunately, only experimental languages, such as Concurrent Pascal or MODULA, contain adequate linguistic constructs for support of such concepts as processes and monitors. The compilers for those languages are available only on a few machines and are devoted primarily to education. In this paper a simple method of extending a PL/I-like programming language by concurrency features is described which is based on the usage of an existing compiler. The method has proven to be a cost effective way of adopting recent research results in existing software engineering tools, thus avoiding the need of switching over to a completely new programming environment.     

基于OOPN的多处理机操作系统设计与实现

大多数实时系统具有事件驱动的并发特性,同时多处理机系统在实时领域得到了广泛的应用。实时系统内在的并发性以及与环境的交互性导致了实时软件复杂的控制结构,使得开发实时软件十分困难。由于PETRI网是一种适合于描述并发的可视化建模语言,有形式化描述。所以,作者采用PETRI网来表示一个实时软件中的并发部分,用普通编程语言实现剩下的顺序程序部分。两级程序设计方法可以更加有效、可靠地开发实时软件。文章涉及的实时操作系统是以RTLinux为基础,对其内核进行扩展,使之支持OOPN1形式的作业描述,并具有实时多处理机调度功能。     

Model based testing in incremental system development

The spiraling nature of evolutionary software development processes produces executable parts of the system at the end of each loop. It is argued that these parts should consist not only of programming language code, but of executable graphical system models. As a main benefit of the use of more abstract, yet formal, modeling languages, a method for model based test sequence generation for reactive systems on the grounds of Constraint Logic Programming as well as its implementation in the CASE tool A F is presented.     

An Implementation of Constructive Synchronous Programs in POLIS

Design tools for embedded reactive systems commonly use a model of computation that employs both synchronous and asynchronous communication styles. We form a junction between these two with an implementation of synchronous languages and circuits (Esterel) on asynchronous networks (POLIS). We implement fact propagation, the key concept of synchronous constructive semantics, on an asynchronous non-deterministic network: POLIS nodes (CFSMs) save state locally to deduce facts, and the network globally propagates facts between them. The result is a correct implementation of the synchronous input/output behavior of the program. Our model is compositional, and thus permits implementations at various levels of granularity from one CFSM per circuit gate to one CFSM per circuit. This allows one to explore various tradeoffs between synchronous and asynchronous implementations.     

Certification of software for real-time safety-critical systems: state of the art

This paper presents an overview and discusses the role of certification in safety-critical computer systems focusing on software, and partially hardware, used in the civil aviation domain. It discusses certification activities according to RTCA DO-178B “Software Considerations in Airborne Systems and Equipment Certification” and touches on tool qualification according to RTCA DO-254 “Design Assurance Guidance for Airborne Electronic Hardware.” Specifically, certification issues as related to real-time operating systems and programming languages are reviewed, as well as software development tools and complex electronic hardware tool qualification processes are discussed. Results of an independent industry survey done by the authors are also presented.