Qualitative and quantitative evaluation of stochastic Time Petri Nets

Time Petri Nets (TPN) are a well-known formalism for modelling time-dependent systems with timing constraints. This paper proposes an approach based on a stochastic extension of TPN (sTPN), which enables both qualitative assessment of feasible temporal behaviors through model checking, and quantitative evaluation of a probability measure of a given behavior, by statistical model checking. The experimental work rests on the use of the latest version of the UPPAAL toolbox which supports both exhaustive non deterministic analysis and statistical model checking of system properties. The approach is demonstrated through an example

Modelling and verification of starvation-free mutual exclusion algorithms based on weak semaphores

This paper proposes an original framework for modelling and verification (M&V) of starvation-free mutual exclusion algorithms based on weak semaphores, that are without a built-in waiting-process queue. The goal is to support the implementation of light-weight starvation-free semaphores useful in general concurrent systems including cyber physical systems. The M&V approach depends on UPPAAL. First known weak semaphores are modelled. Then they are exploited for model checking classic algorithms. Known properties are retrieved but subtle new ones are discovered. As part of the developed approach, a new algorithm is proposed which uses two semaphores of the weakest type, N bits (N being the number of processes) and a counter. This algorithm too is proved to be correct

model checking mutual exclusion algorithms using uppaal

This paper proposes an approach to modelling and exhaustive verification of mutual exclusion algorithms which is based on Timed Automata in the context of the popular Uppaal toolbox. The approach makes it possible to study the properties of a mutual exclusion algorithm also in the presence of the time dimension. For demonstration purposes some historical algorithms are modelled and thoroughly analyzed, going beyond some informal reasoning reported in the literature. The paper also proposes a mutual exclusion algorithm for $N \ge 2$ processes whose model checking confirms it satisfies all the required properties

Modelling and Simulation of Asynchronous Real-Time Systems using Timed Rebeca

In this paper we propose an extension of the Rebeca language that can be used to model distributed and asynchronous systems with timing constraints. We provide the formal semantics of the language using Structural Operational Semantics, and show its expressiveness by means of examples. We developed a tool for automated translation from timed Rebeca to the Erlang language, which provides a first implementation of timed Rebeca. We can use the tool to set the parameters of timed Rebeca models, which represent the environment and component variables, and use McErlang to run multiple simulations for different settings. Timed Rebeca restricts the modeller to a pure asynchronous actor-based paradigm, where the structure of the model represents the service oriented architecture, while the computational model matches the network infrastructure. Simulation is shown to be an effective analysis support, specially where model checking faces almost immediate state explosion in an asynchronous setting.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Performance of Parallel K-Means Algorithms in Java

K-means is a well-known clustering algorithm often used for its simplicity and potential efficiency. Its properties and limitations have been investigated by many works reported in the literature. K-means, though, suffers from computational problems when dealing with large datasets with many dimensions and great number of clusters. Therefore, many authors have proposed and experimented different techniques for the parallel execution of K-means. This paper describes a novel approach to parallel K-means which, today, is based on commodity multicore machines with shared memory. Two reference implementations in Java are developed and their performances are compared. The first one is structured according to a map/reduce schema that leverages the built-in multi-threaded concurrency automatically provided by Java to parallel streams. The second one, allocated on the available cores, exploits the parallel programming model of the Theatre actor system, which is control-based, totally lock-free, and purposely relies on threads as coarse-grain “programming-in-the-large” units. The experimental results confirm that some good execution performance can be achieved through the implicit and intuitive use of Java concurrency in parallel streams. However, better execution performance can be guaranteed by the modular Theatre implementation which proves more adequate for an exploitation of the computational resources

Admission Control in Home Energy Management Systems Using Theatre and Hybrid Actors

The goal of a Home Energy Management System (HEMS) is that of purposely shaping the cumulative energy consumption curves of domestic appliances by imposing suitable monitoring and control policies. The development of HEMS, like the development of general Cyber-Physical Systems (CPSs), is challenging, as it requires the exploitation of suitable methodological approaches which are able to deal jointly with the continuous and discrete behaviours of a CPS. In this paper, a methodological approach for HEMS is advocated which relies on the use of the Theatre actor system with hybrid actors. As a key feature, Theatre enables the same actor model to be used during the analysis, design, prototyping and implementation phases of the system. For property assessment, a Theatre model is reduced to Uppaal hybrid timed automata for analysis by statistical model checking. As a significant modelling example, a HEMS is proposed which implements an admission control strategy able to maintain the in-home energy consumption under a given threshold. Instead of reacting to an overload condition, the strategy is able to prevent an overload upfront by predicting the effect that the admission of a new load will have on the consumption curve of the whole system