Reversibility in session-based concurrency: A fresh look

Much research has studied foundations for correct and reliable communication-centric software systems. A salient approach to correctness uses verification based on session types to enforce structured communications; a recent approach to reliability uses reversible actions as a way of reacting to unanticipated events or failures. In this paper, we develop a simple observation: the semantic machinery required to define asynchronous (queue-based), monitored communications can also support reversible protocols. We propose a framework of session communication in which monitors support reversibility of (untyped) processes. Main novelty in our approach are session types with present and past, which allow us to streamline the semantics of reversible actions. We prove that reversibility in our framework is causally consistent, and define ways of using monitors to control reversible actions. Keyword

The Internet of Things and The Web of Things

International audienceThe Internet of Things is creating a new world, a quantifiable and measureable world, where people and businesses can manage their assets in better informed ways, and can make more timely and better informed decisions about what they want or need to do. This new con-nected world brings with it fundamental changes to society and to consumers. This special issue of ERCIM News thus focuses on various relevant aspects of the Internet of Things and the Web of Things

Functional Programming for Embedded Systems

Embedded Systems application development has traditionally been carried out in low-level machine-oriented programming languages like C or Assembler that can result in unsafe, error-prone and difficult-to-maintain code. Functional programming with features such as higher-order functions, algebraic data types, polymorphism, strong static typing and automatic memory management appears to be an ideal candidate to address the issues with low-level languages plaguing embedded systems. However, embedded systems usually run on heavily memory-constrained devices with memory in the order of hundreds of kilobytes and applications running on such devices embody the general characteristics of being (i) I/O- bound, (ii) concurrent and (iii) timing-aware. Popular functional language compilers and runtimes either do not fare well with such scarce memory resources or do not provide high-level abstractions that address all the three listed characteristics. This work attempts to address this gap by investigating and proposing high-level abstractions specialised for I/O-bound, concurrent and timing-aware embedded-systems programs. We implement the proposed abstractions on eagerly-evaluated, statically-typed functional languages running natively on microcontrollers. Our contributions are divided into two parts - Part 1 presents a functional reactive programming language - Hailstorm - that tracks side effects like I/O in its type system using a feature called resource types. Hailstorm’s programming model is illustrated on the GRiSP microcontroller board.Part 2 comprises two papers that describe the design and implementation of Synchron, a runtime API that provides a uniform message-passing framework for the handling of software messages as well as hardware interrupts. Additionally, the Synchron API supports a novel timing operator to capture the notion of time, common in embedded applications. The Synchron API is implemented as a virtual machine - SynchronVM - that is run on the NRF52 and STM32 microcontroller boards. We present programming examples that illustrate the concurrency, I/O and timing capabilities of the VM and provide various benchmarks on the response time, memory and power usage of SynchronVM

Time for Reactive System Modeling

Reactive systems interact with their environment by reading inputs and computing and feeding back outputs in reactive cycles that are also called ticks. Often they are safety critical systems and are increasingly modeled with highlevel modeling tools. The concepts of the corresponding modeling languages are typically aimed to facilitate formal reasoning about program constructiveness to guarantee deterministic output and are explicitly abstracted from execution time aspects. Nevertheless, the worst-case execution time of a tick can be a crucial value, where exceedance can lead to lost inputs or tardy reaction to critical events. This thesis proposes a general approach to interactive timing analysis, which enables the feedback of detailed timing values directly in the model representation to support timing aware modeling. The concept is based on a generic timing interface that enables the exchangeability of the modeling as well as the timing analysis tool for the flexible implementation of varying tool chains. The proposed timing analysis approach includes visual highlighting and modeling pragmatics features to guide the user to timing hotspots for timing related model revisions

Compilation de systèmes temps réel

I introduce and advocate for the concept of Real-Time Systems Compilation. By analogy with classical compilation, real-time systems compilation consists in the fully automatic construction of running, correct-by-construction implementations from functional and non-functional specifications of embedded control systems. Like in a classical compiler, the whole process must be fast (thus enabling a trial-and-error design style) and produce reasonably efficient code. This requires the use of fast heuristics, and the use of fine-grain platform and application models. Unlike a classical compiler, a real-time systems compiler must take into account non-functional properties of a system and ensure the respect of non-functional requirements (in addition to functional correctness). I also present Lopht, a real-time systems compiler for statically-scheduled real-time systems we built by combining techniques and concepts from real-time scheduling, compilation, and synchronous languages

Verification of Concurrent Systems : optimality, Scalability and Applicability

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Informática, leída el 14-10-2020Tanto el testing como la verificacion de sistemas concurrentes requieren explorar todos los posibles entrelazados no deterministas que la ejecucion concurrente puede tener, ya que cualquiera de estos entrelazados podra revelar un comportamiento erroneo del sistema. Esto introduce una explosion combinatoria en el numero de estados del programa que deben ser considerados, lo que frecuentemente lleva a un problema computacionalmente intratable. El objetivo de esta tesis es el desarrollo de tecnicas novedosas para el testing y la verificacion de programas concurrentes que permitan reducir esta explosion combinatoria...Both verification and testing of concurrent systems require exploring all possible non-deterministic interleavings that the concurrent execution may have, as any of the interleavings may reveal an erroneous behavior of the system. This introduces a combinatorial explosion on the number of program states that must be considered, what leads often to a computationally intractable problem. The overall goal of this thesis is to investigate novel techniques for testing and verification of concurrent programs that reduce this combinatorial explosion...Fac. de InformáticaTRUEunpu

Interactive Model-Based Compilation: A Modeller-Driven Development Approach

There is a growing tendency for using domain-specific languages, which help domain experts to stay focussed on abstract problem solutions. It is important to carefully design these languages and tools, which fundamentally perform model-to-model transformations. The quality of both usually decides the effectiveness of the subsequent development and therefore the quality of the final applications. However, as the complexity and safety requirements of modern systems grow, it becomes increasingly burdensome to create highly customized languages and difficult to provide reasonable overviews within these tools. This thesis introduces a new interactive model-based compilation methodology. Compilations for arbitrary model-to-model transformations are themselves described as models. They can be instantiated for particular inputs, e. g. a program, to create concrete compilation runs, which return the result of that compilation. The compilation instance is interactively observable. Intermediate results serve as new inputs and as documentation. They can be used to create highly customized views and facilitate understandability. This methodology guides modellers from the start of the compilation to the final result so that they can interactively refine their models. The methodology has been implemented and validated as the KIELER Compiler (KiCo) and is available as part of the KIELER open-source project. It is used to implement the current reference compiler for the SCCharts language, a statecharts dialect designed for specifying safety-critical reactive systems based on a synchronous model of computation. The interactive model-based compilation approach was key to the rapid prototyping of three different compilation strategies, as well as new language extensions, variations and closely related languages. The results are verified with benchmarks, which are again modelled using the same approach and technology. The usability of the SCCharts language and the KiCo tooling is documented with long-term surveys and real-life industrial, academic and teaching examples