Joaquin Aguado

Sequentially constructive concurrency: a conservative extension of the synchronous model of computation

Synchronous languages ensure deterministic concurrency, but at the price of heavy restrictions on what programs are considered valid, or constructive. Meanwhile, sequential languages such as C and Java offer an intuitive, familiar programming paradigm but provide no guarantees with regard to deterministic concurrency. The sequentially constructive model of computation (SC MoC) presented here harnesses the synchronous execution model to achieve deterministic concurrency while addressing concerns that synchronous languages are unnecessarily restrictive and difficult to adopt. In essence, the SC MoC extends the classical synchronous MoC by allowing variables to be read and written in any order as long as sequentiality expressed in the program provides sufficient scheduling information to rule out race conditions. The SC MoC is a conservative extension in that programs considered constructive in the common synchronous MoC are also SC and retain the same semantics. In this paper, we identify classes of variable accesses, define sequential constructiveness based on the concept of SC-admissible scheduling, and present a priority-based scheduling algorithm for analyzing and compiling SC programs.

SCCharts: sequentially constructive statecharts for safety-critical applications: HW/SW-synthesis for a conservative extension of synchronous statecharts

We present a new visual language, SCCharts, designed for specifying safety-critical reactive systems. SCCharts use a statechart notation and provide determinate concurrency based on a synchronous model of computation (MoC), without restrictions common to previous synchronous MoCs. Specifically, we lift earlier limitations on sequential accesses to shared variables, by leveraging the sequentially constructive MoC. The semantics and key features of SCCharts are defined by a very small set of elements, the Core SCCharts, consisting of state machines plus fork/join concurrency. We also present a compilation chain that allows efficient synthesis of software and hardware.

Grounding Synchronous Deterministic Concurrency in Sequential Programming

Using a new domain-theoretic characterisation we show that Berrys constructive semantics is a conservative approximation of the recently proposed sequentially constructive SC model of computation. We prove that every Berry-constructive program is deterministic and deadlock-free under sequentially admissible scheduling. This gives, for the first time, a natural interpretation of Berry-constructiveness for shared-memory, multi-threaded programming in terms of synchronous cycle-based scheduling, where previous results were cast in terms of synchronous circuits. This opens the door to a direct mapping of Esterels signal mechanism into boolean variables that can be set and reset under the programmers control within a tick. We illustrate the practical usefulness of this mapping by discussing how signal reincarnation is handled efficiently by this transformation, which is of linear complexity in program size, in contrast to earlier techniques that had quadratic overhead.

Sequentially Constructive Concurrency—A Conservative Extension of the Synchronous Model of Computation

Synchronous languages ensure deterministic concurrency, but at the price of heavy restrictions on what programs are considered valid, or constructive. Meanwhile, sequential languages such as C and Java offer an intuitive, familiar programming paradigm but provide no guarantees with regard to deterministic concurrency. The sequentially constructive model of computation (SC MoC) presented here harnesses the synchronous execution model to achieve deterministic concurrency while addressing concerns that synchronous languages are unnecessarily restrictive and difficult to adopt. In essence, the SC MoC extends the classical synchronous MoC by allowing variables to be read and written in any order as long as sequentiality expressed in the program provides sufficient scheduling information to rule out race conditions. The SC MoC is a conservative extension in that programs considered constructive in the common synchronous MoC are also SC and retain the same semantics. In this paper, we identify classes of variable accesses, define sequential constructiveness based on the concept of SC-admissible scheduling, and present a priority-based scheduling algorithm for analyzing and compiling SC programs.

Constructive semantics for instantaneous reactions

This paper presents some results towards a game-theoretic account of the constructive semantics of step responses for synchronous languages, providing a coherent semantic framework encompassing both non-deterministic Statecharts (as per Pnueli & Shalev) and deterministic esterel. In particular, it is shown that esterel arises from a finiteness condition on strategies whereas Statecharts permits infinite games. Beyond giving a novel and unifying account of these concrete languages the paper sketches a general theory for obtaining different notions of constructive responses in terms of winning conditions for finite and infinite games and their characterisation as maximal post-fixed points of functions in directed complete lattices of intensional truth-values.

A--maze--ing Esterel

This paper shows that the kernel fragment of Esterel corresponding to combinational circuits admits a natural game{theoretic interpretation. Technically, combinational Esterel programs are mapped into nite two{player games in such a way that the standard must{ and cannot{analysis of signal statuses is reected in the computation of winning strategies. The novel game{theoretic approach complements the existing behavioral, operational, circuit{based, and model{theoretic accounts of Esterel’s semantics and oers a new didactic perspective for familiarizing students and engineers with this intricate constructive semantics.

Deterministic Concurrency: A Clock-Synchronised Shared Memory Approach

Synchronous Programming (SP) is a universal computational principle that provides deterministic concurrency. The same input sequence with the same timing always results in the same externally observable output sequence, even if the internal behaviour generates uncertainty in the scheduling of concurrent memory accesses. Consequently, SP languages have always been strongly founded on mathematical semantics that support formal program analysis. So far, however, communication has been constrained to a set of primitive clock-synchronised shared memory (csm) data types, such as data-flow registers, streams and signals with restricted read and write accesses that limit modularity and behavioural abstractions.

A Multi-objective Hospital Operating Room Planning and Scheduling Problem Using Compromise Programming

This paper proposes a hybrid compromise programming local search approach with two main characteristics: a capacity to generate non-dominated solutions and the ability to interact with the decision maker. Compromise programming is an approach where it is not necessary to determine the entire set of Pareto-optimal solutions but only some of them. These solutions are called compromise solutions and represent a good tradeoff between conflicting objectives. Another advantage of this type of method is that it allows the inclusion of the decision maker’s preferences through the definition of weights included in the different metrics used by the method. This approach is tested on an operating room planning process. This process incorporates the operating rooms and the nurse planning simultaneously. Three different objectives were considered: to minimize operating room costs, to minimize the maximum number of nurses needed to participate in surgeries and to minimize the number of open operating rooms. The results show that it is a powerful decision tool that enables the decision makers to apply compromise alongside optimal solutions during an operating room planning process.

Computing with streams

In functional programming, the general technique for supporting stream-based computations is by means of (higher-order) functions external to the underline streams structure. The proposal of this paper is orthogonal to this view and it is based on an alternative representation of streams that allows employing different functions as streams constructors (re-constructors). The internal computation prescribed by a stream is realised by constructing the stream with its own re-constructors. This provides us with a computationally more active and self-contained streams notion that allows: (1) deriving new re-constructors by combining other re-constructors, (2) specifying dataflow computations directly inside streams and, dually, (3) defining re-constructors out of dataflow combinators. Moreover, this modelling supports to some degree parallel (sequential) evaluations of unbounded (recursive) structures in the style of Evaluation Strategies. All these possibilities are achieved thanks to a comonadic development able to capture co-inductive streams, parallelism (sequentiality) and causality aspects directly.