Reversibility in Massive Concurrent Systems

Reversing a (forward) computation history means undoing the history. In concurrent systems, undoing the history is not performed in a deterministic way but in a causally consistent fashion, where states that are reached during a backward computation are states that could have been reached during the computation history by just performing independent actions in a different order.Comment: Presented at MeCBIC 201

A framework for deadlock detection in core ABS

We present a framework for statically detecting deadlocks in a concurrent object-oriented language with asynchronous method calls and cooperative scheduling of method activations. Since this language features recursion and dynamic resource creation, deadlock detection is extremely complex and state-of-the-art solutions either give imprecise answers or do not scale. In order to augment precision and scalability we propose a modular framework that allows several techniques to be combined. The basic component of the framework is a front-end inference algorithm that extracts abstract behavioural descriptions of methods, called contracts, which retain resource dependency information. This component is integrated with a number of possible different back-ends that analyse contracts and derive deadlock information. As a proof-of-concept, we discuss two such back-ends: (i) an evaluator that computes a fixpoint semantics and (ii) an evaluator using abstract model checking.Comment: Software and Systems Modeling, Springer Verlag, 201

ENSINANDO A ENSINAR: DIRETRIZES E ESTRATÉGIAS PARA MELHORAR A FORMAÇÃO DE PROFESSORES NO ENSINO SUPERIOR

The debate on the quality of university teacher education is more than ever a relevant issue. It is a topic which frequently appears in specialized journals about Higher Education and is often examined in a scientific context. This article takes up some of these complicated issues and illustrates with examples taken from a study at the University of Bari.El debate sobre la calidad de la formación del profesorado universitario es más que nunca un tema relevante. Es un tema que a menudo aparece en revistas especializadas sobre educación superior que a menudo se examinan en el contexto científico. Este artículo aborda algunos de estos problemas complejos y los ilustra con ejemplos de un estudio realizado por la Universidad de Bari.O debate sobre a qualidade da formação de professores universitários é mais do que nunca uma questão relevante. É um tópico que frequentemente aparece em periódicos especializados sobre ensino superior frequentemente examinado no contexto científico. Este artigo aborda algumas dessas questões complexas e as ilustra com exemplos retirados de um estudo da Universidade de Bari

A Formal Analysis of the Bitcoin Protocol

none2noWe study Nakamoto’s Bitcoin protocol that implements a distributed ledger on peer-to-peer asynchronous networks. In particular, we define a principled formal model of key participants - the miners - as stochastic processes and describe the whole system as a parallel composition of miners. We therefore compute the probability that ledgers turn into a state with more severe inconsistencies, e.g. with longer forks, under the assumptions that messages are not lost and nodes are not hostile. We also study how the presence of hostile nodes mining blocks in wrong positions impacts on the consistency of the ledgers. Our theoretical results agree with the simulations performed on a probabilistic model checker that we extended with dynamic datatypes in order to have a faithful description of miners' behaviour.openAdele Veschetti, Cosimo LaneveAdele Veschetti, Cosimo Lanev

Deadlock Analysis of Wait-Notify Coordination

International audienceDeadlock analysis of concurrent programs that contain coordination primitives (wait, notify and notifyAll) is notoriously challenging. Not only these primitives affect the scheduling of processes, but also notifications unmatched by a corresponding wait are silently lost. We design a behavioral type system for a core calculus featuring shared objects and Java-like coordination primitives. The type system is based on a simple language of object protocols-called usages-to determine whether objects are used reliably, so as to guarantee deadlock freedom

A lightweight deadlock analysis for programs with threads and reentrant locks

International audienceDeadlock analysis of multi-threaded programs with reentrant locks is complex because these programs may have infinitely many states. We define a simple calculus featuring recursion, threads and synchroniza-tions that guarantee exclusive access to objects. We detect deadlocks by associating an abstract model to programs-the extended lam model-and we define an algorithm for verifying that a problematic object dependency (e.g. a circularity) between threads will not be manifested. The analysis is lightweight because the deadlock detection problem is fully reduced to the corresponding one in lams (without using other models). The technique is intended to be an effective tool for the deadlock analysis of programming languages by defining ad-hoc extraction processes

Interaction systems I : the theory of optimal reductions

Projet PARAA new class of higher order rewriting systems, called interaction systems is introduced. From one side, interaction systems provide the intuitionistic generalization of Lafont's interaction nets (recall that interaction nets are linear). In particular, we keep the idea of binary interaction and the syntactical bipartition of operators into constructors and destructors. From the other side, interaction systems are the subsystem of Klop's combinatory reduction systems where the Curry-Howard analogy stoll "makes sense". This means that we can associate with every IS a suitable logical (intuitionistic) system ; constructors and destructors respectively correspond to right and left introduction rules, interaction is cut and computation is cut-elimination. Interaction systems have been primarily motivated by the necessity of extending Lamping's optimal graph reduction technique for the l-calculus to other computational constructs than just -reduction. This implementation style can be smootly generalized to arbitrary IS's providing in this way a uniform description of essential rules such as conditionals and recursion The optimal implementation of IS's will be only sketched here (it will eventually be the subject of the forthcoming Part II). The main aim of this paper is to introduce this new class of systems, to discuss the motivations behind its definition and to investigate the theoretical aspect of optimal reductions (in particular, the notion of redex-family)