Proceedings 18th International Workshop on Expressiveness in Concurrency (Aachen, Germany, September 5, 2011)

This volume contains the proceedings of the 18th International Workshop on Expressiveness in Concurrency (EXPRESS 2011), which took place on 5th September 2011 in Aachen, as a satellite workshop of CONCUR 2011. The EXPRESS workshop series aim at bringing together researchers who are interested in the expressiveness and comparison of formal models that broadly relate to concurrency. In particular, this also includes emergent fields such as logic and interaction, game-theoretic models, and service-oriented computing

Causal Reversibility in Individual Token Interpretation of Petri Nets

Causal reversibility in concurrent systems means that events that the origin of other events can only be undone after undoing of its consequences. In opposite to backtracking, the events which are independent of each other can be reversed in an arbitrary order, in the other words, we have flexible reversibility w.r.t the causality relation. An implementation of Individual token interpretation ofPetri Nets (IPNs) was been proposed by Rob Van Glabbeek et al, the present paper investigates into a study of causal reversibility within IPNs. Given N be an IPN, by adding an intuitive firing rule to undo transitions according to the causality relation, the coherence of N is assured, i.e., the set of all reachable states of N in the reversible version and that of the original one are identical. Furthermore, reversibility in N is flexible and their initial state can be accessible in reverse from any state. In this paper an approach for controllingcausal-reversibility within IPNs is proposed

Actor programming with static guarantees

This thesis discusses two methodologies for applying type discipline to concurrent programming with actors: process types, and session types. A system based on each of the two is developed, and used as the basis for a comprehensive overview of process- and session- type merits and limitations. In particular, we analyze the trade-offs of the two approaches with regard to the expressiveness of the resulting calculi, versus the nature of the static guarantees offered. The first system discussed is based on the notion of a \emph{typestate}, that is, a view of an actor's internal state that can be statically tracked. The typestates used here capture what each actor handle \emph{may} be used for, as well as what it \emph{must} be used for. This is done by associating two kinds of tokens with each actor handle: tokens of the first kind are consumed when the actor receives a message, and thus dictate the types of messages that can be sent through the handle; tokens of the second kind dictate messaging obligations, and the type system ensures that related messages have been sent through the handle by the end of its lifetime. The next system developed here adapts session types to suit actor programming. Session types come from the world of process calculi, and are a means to statically check the messaging taking place over communication channels against a pre-defined protocol. Since actors do not use channels, one needs to consider pairs of actors as participants in multiple, concurrently executed---and thus interleaving---protocols. The result is a system with novel, parameterized type constructs to capture communication patterns that prior work cannot handle, such as the sliding window protocol. Although this system can statically verify the implementation of complicated messaging patterns, it requires deviations from industry-standard programming models---a problem that is true for all session type systems in the literature. This work argues that the typestate-based system, while not enforcing protocol fidelity as the session-inspired one does, is nevertheless more suitable for model actor calculi adopted by practical, already established frameworks such as Erlang and Akka

Twenty years of rewriting logic

AbstractRewriting logic is a simple computational logic that can naturally express both concurrent computation and logical deduction with great generality. This paper provides a gentle, intuitive introduction to its main ideas, as well as a survey of the work that many researchers have carried out over the last twenty years in advancing: (i) its foundations; (ii) its semantic framework and logical framework uses; (iii) its language implementations and its formal tools; and (iv) its many applications to automated deduction, software and hardware specification and verification, security, real-time and cyber-physical systems, probabilistic systems, bioinformatics and chemical systems

Programmiersprachen und Rechenkonzepte

Seit 1984 veranstaltet die GI--Fachgruppe "Programmiersprachen und Rechenkonzepte" regelmäßig im Frühjahr einen Workshop im Physikzentrum Bad Honnef. Das Treffen dient in erster Linie dem gegenseitigen Kennenlernen, dem Erfahrungsaustausch, der Diskussion und der Vertiefung gegenseitiger Kontakte

Behavioural Preorders on Stochastic Systems - Logical, Topological, and Computational Aspects

Computer systems can be found everywhere: in space, in our homes, in our cars, in our pockets, and sometimes even in our own bodies. For concerns of safety, economy, and convenience, it is important that such systems work correctly. However, it is a notoriously difficult task to ensure that the software running on computers behaves correctly. One approach to ease this task is that of model checking, where a model of the system is made using some mathematical formalism. Requirements expressed in a formal language can then be verified against the model in order to give guarantees that the model satisfies the requirements. For many computer systems, time is an important factor. As such, we need our formalisms and requirement languages to be able to incorporate real time. We therefore develop formalisms and algorithms that allow us to compare and express properties about real-time systems. We first introduce a logical formalism for reasoning about upper and lower bounds on time, and study the properties of this formalism, including axiomatisation and algorithms for checking when a formula is satisfied. We then consider the question of when a system is faster than another system. We show that this is a difficult question which can not be answered in general, but we identify special cases where this question can be answered. We also show that under this notion of faster-than, a local increase in speed may lead to a global decrease in speed, and we take step towards avoiding this. Finally, we consider how to compare the real-time behaviour of systems not just qualitatively, but also quantitatively. Thus, we are interested in knowing how much one system is faster or slower than another system. This is done by introducing a distance between systems. We show how to compute this distance and that it behaves well with respect to certain properties.Comment: PhD dissertation from Aalborg Universit

Multi-GPU support on the marrow algorithmic skeleton framework

Dissertação para obtenção do Grau de Mestre em Engenharia InformáticaWith the proliferation of general purpose GPUs, workload parallelization and datatransfer optimization became an increasing concern. The natural evolution from using a single GPU, is multiplying the amount of available processors, presenting new challenges, as tuning the workload decompositions and load balancing, when dealing with heterogeneous systems. Higher-level programming is a very important asset in a multi-GPU environment, due to the complexity inherent to the currently used GPGPU APIs (OpenCL and CUDA), because of their low-level and code overhead. This can be obtained by introducing an abstraction layer, which has the advantage of enabling implicit optimizations and orchestrations such as transparent load balancing mechanism and reduced explicit code overhead. Algorithmic Skeletons, previously used in cluster environments, have recently been adapted to the GPGPU context. Skeletons abstract most sources of code overhead, by defining computation patterns of commonly used algorithms. The Marrow algorithmic skeleton library is one of these, taking advantage of the abstractions to automate the orchestration needed for an efficient GPU execution. This thesis proposes the extension of Marrow to leverage the use of algorithmic skeletons in the modular and efficient programming of multiple heterogeneous GPUs, within a single machine. We were able to achieve a good balance between simplicity of the programming model and performance, obtaining good scalability when using multiple GPUs, with an efficient load distribution, although at the price of some overhead when using a single-GPU.projects PTDC/EIA-EIA/102579/2008 and PTDC/EIA-EIA/111518/200