Imperative Synchronous Languages Research Articles

Synchronized Shared Memory and Black-box Procedural Abstraction: Toward a Formal Semantics of Blech

Traditional imperative synchronous programming languages heavily rely on a strict separation between data memory and communication signals. Signals can be shared between computational units but cannot be overwritten within a synchronous reaction cycle. Memory can be destructively updated but cannot be shared between concurrent threads. This incoherence makes traditional imperative synchronous languages cumbersome for the programmer. The recent definition of sequentially constructive synchronous languages offers an improvement. It removes the separation between data memory and communication signals and unifies both through the notion of clock synchronized shared memory . However, it still depends on global causality analyses, which precludes black-box procedural abstraction. This complicates reuse and composition of software components. This article shows how black-box procedural abstraction can be accommodated inside the sequentially constructive model of computation. We present the Sequentially Constructive Procedural Language ( SCoPL ) and its semantic theory of policy-constructive synchronous processes. SCoPL supports black-box procedural abstractions using policy interfaces to ensure that procedure calls are memory-safe and wait-free and their scheduling is determinate and causal. At the same time, a policy interface constrains the level of freedom for the implementation and subsequent refactoring of a procedure. As a result, policies enable separate compilation and composition of procedures. We present our extensions abstractly as a formal semantics for SCoPL and motivate it concretely in the context of the open-source, embedded, real-time language Blech .

Synchronous Deterministic Parallel Programming for Multi-Cores with ForeC

Embedded real-time systems are tightly integrated with their physical environment. Their correctness depends both on the outputs and timeliness of their computations. The increasing use of multi-core processors in such systems is pushing embedded programmers to be parallel programming experts. However, parallel programming is challenging because of the skills, experiences, and knowledge needed to avoid common parallel programming traps and pitfalls. This article proposes the ForeC synchronous multi-threaded programming language for the deterministic, parallel, and reactive programming of embedded multi-cores. The synchronous semantics of ForeC is designed to greatly simplify the understanding and debugging of parallel programs. ForeC ensures that ForeC programs can be compiled efficiently for parallel execution and be amenable to static timing analysis. ForeC’s main innovation is its shared variable semantics that provides thread isolation and deterministic thread communication. All ForeC programs are correct by construction and deadlock free because no non-deterministic constructs are needed. We have benchmarked our ForeC compiler with several medium-sized programs (e.g., a 2.274-line ForeC program with up to 26 threads and distributed on up to 10 cores, which was based on a 2.155-line non-multi-threaded C program). These benchmark programs show that ForeC can achieve better parallel performance than Esterel, a widely used imperative synchronous language for concurrent safety-critical systems, and is competitive in performance to OpenMP, a popular desktop solution for parallel programming (which implements classical multi-threading, hence is intrinsically non-deterministic). We also demonstrate that the worst-case execution time of ForeC programs can be estimated to a high degree of precision.

Clock refinement in imperative synchronous languages

The synchronous model of computation divides the program execution into a sequence of logical steps. On the one hand, this view simplifies many analyses and synthesis procedures, but on the other hand, it imposes restrictions on the modeling and optimization of systems. In this article, we introduce refined clocks in imperative synchronous languages to overcome these restrictions while still preserving important properties of the basic model. We first present the idea in detail and motivate various design decisions with respect to the language extension. Then, we sketch all the adaptations needed in the design flow to support refined clocks.

Detection of harmful schizophrenic statements in esterel

In imperative synchronous languages, a statement is called schizophrenic if it is executed more than once in a single clock. When a schizophrenic statement is translated into a circuit, the circuit can behave abnormally because of the multiple executions. To solve the problems caused by schizophrenic statements, compilers duplicate the statements to avoid multiple executions. Esterel is an imperative synchronous language. Schizophrenic statements in Esterel are considered to occur due to the instantaneous reentrance of local signal declarations or parallel statements. However, if the corresponding circuit of a schizophrenic statement behaves normally, it is harmless and thus curing is not necessary. In this paper, we identify the conditions under which a schizophrenic statement of the Esterel program must be cured during circuit translation. We also propose an algorithm to detect schizophrenic statements that have to be cured on the control flow graphs (CFGs) of source codes. Our algorithm detects all schizophrenic statements that have to be cured and results in fewer false alarms on the benchmark programs used in the previous work. It is simple and based on the CFG of a program, implying that it can be merged into existing compilers easily.

Over-Approximated Control Flow Graph Construction on Pure Esterel

Esterel is an imperative synchronous language for control-dominant reactive systems. Regardless of imperative features of Esterel, combination of parallel execution and preemption makes it difficult to build control flow graphs (CFGs) of Esterel programs. Simple and convenient CFGs can help to analyze Esterel programs. However, previous researches are not suitable for flow analyses of imperative languages. In this work, we present a method to construct over-approximated CFGs for Pure Esterel. Generated CFGs expose invisible interferences among threads and show program structures explicitly so that they are useful for program analyses based on graph theory or control-/data- flows.

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.

Computational model for distributed multimedia applications based on a synchronous programming language

Distributed multimedia applications pose new, interesting challenges in distributed operating system support. This paper focuses on a computational model, i.e. a set of programming system interface abstractions, well-suited for distributed multimedia applications. The paper advocates a mixed approach, based on the use of synchronous languages for programming multimedia synchronization. In particular, we discuss the use of ESTEREL, an imperative synchronous language, as a basic constituent of our mixed computational model, the usefulness and practicality of its semantic features, and its embedding in an asynchronous distributed system.