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

Deadlock-Guided Testing in CLP

Static deadlock analyzers might be able to verify the absence of deadlock. However, they are usually not able to detect its presence. Also, when they detect a potential deadlock cycle, they provide little (or even no) information on their output. Due to the complex flow of concurrent programs, the user might not be able to find the source of the anomalous behaviour from the abstract information computed by static analysis. This work proposes the combined use of static analysis and testing for effective deadlock detection in asynchronous programs. The asynchronous program is first translated into a CLP-version so that the whole combined approach is carried out by relying on the inherent backtracking mechanism and constraint handling of CLP. When the program features a deadlock, our combined use of analysis and testing provides an effective technique to catch deadlock traces. While if the program does not have deadlock, but the analyzer inaccurately spotted it, we might be able to prove deadlock freedom. The main results in this project have been submitted to: - the special issue on Computational Logic for Verification of the journal Theory and Practice of Logic Programming and - the 27th International Symposium on Logic-Based Program Synthesis and Transformation (LOPSTR'17), and are currently under revision

Performance evaluation and model checking of probabilistic real-time actors

This dissertation is composed of two parts. In the first part, performance evaluation and verification of safety properties are provided for real-time actors. Recently, the actor-based language, Timed Rebeca, was introduced to model distributed and asynchronous systems with timing constraints and message passing communication. A toolset was developed for automated translation of Timed Rebeca models to Erlang. The translated code can be executed using a timed extension of McErlang for model checking and simulation. In the first part of this dissertation, we induce a new toolset that provides statistical model checking of Timed Rebeca models. Using statistical model checking, we are now able to verify larger models against safety properties comparing to McErlang model checking. We examine the typical case studies of elevators and ticket service to show the efficiency of statistical model checking and applicability of our toolset. In the second part of this dissertation, we enhance our modeling ability and cover more properties by performance evaluation and model checking of probabilistic real-time actors. Distributed systems exhibit probabilistic and nondeterministic behaviors and may have time constraints. Probabilistic Timed Rebeca (PTRebeca) is introduced as a timed and probabilistic actor-based language for modeling distributed real-time systems with asynchronous message passing. The semantics of PTRebeca is a Timed Markov Decision Process (TMDP). We provide SOS rules for PTRebeca, and develop two toolsets for analyzing PTRebeca models. The first toolset automatically generates a TMDP model from a PTRebeca model in the form of the input language of the PRISM model checker. We use PRISM for performance analysis of PTRebeca models against expected reachability and probabilistic reachability properties. Additionally, we develop another toolset to automatically generate a Markov Automaton from a PTRebeca model in the form of the input language of the Interactive Markov Chain Analyzer (IMCA). The IMCA can be used as the back-end model checker for performance analysis of PTRebeca models against expected reachability and probabilistic reachability properties. We present the needed time for the analysis of different case studies using PRISM-based and IMCA-based approaches. The IMCA-based approach needs considerably less time, and so has the ability of analyzing significantly larger models. We show the applicability of both approaches and the efficiency of our tools by analyzing a few case studies and experimental results.Þessi ritgerð er tvískipt. Í fyrri hlutanum er farið í mat og sannprófun á eiginleikum öryggis í rauntímalíkönum. Fyrir stuttu síðan var leikendabyggða málið, Timed Rebeca, notað við líkana dreifingu og ósamstillt kerfi með tímastillingu og samskipti í skilaboðum. Búið var til verkfærasett fyrir sjálfvirka þýðingu á Timed Rebeca líkön yfir í Erlang. Hægt er að nota þýdda kóðann með því að nota tímastillta framlengingu af McErlang fyrir líkanaprófun og hermun. Í fyrri hluta þessarar ritgerðar, ætlum við að kynna verkfærasettið sem veitir tölfræðilega prófun á líkön á Timed Rebeca líkön. Með því að nota tölfræðileg próf á líkön er núna hægt að sannreyna stærri líkön eins og í öryggiskröfum McErlang. Við rannsökum dæmigerðar ferilsathuganir af lyftum og miðasölu til að sýna fram á skilvirkni tölfræðilegra líkana og beitingu verkfærasettsins okkar. Í seinni hluta þessarar ritgerðar aukum við við getu líkanagerðarinnar og við náum yfir fleiri eiginleika með mati á framkvæmd og prófunum á líkönum á líkinda rauntíma leikara. Dreifð kerfi sýna líkindi og brigðgenga hegðun sem kunna að hafa tímamörk. Probabilistic Timed Rebeca (PTRebeca) er kynnt sem tímastillt og líkinda leikarabyggt mál líkindadreifðra rauntímakerfa með ósamstillta sendingu skilaboða. Merkingarfræði PTRebeca er Timed Markov Decision Process (TMDP). Við verðum með SOS reglur fyrir PTRebeca, og þróum tvö verkfærasett til að greina PTRebeca líkön.The work on this dissertation was supported by the project "Timed Asynchronous Reactive Objects in Distributed Systems: TARO" (nr.110020021) of the Icelandic Research Fund

Static analysis of concurrrent and distributed systems: concurrent objects and Ethereum Bytecode

Tesis de la Universidad Complutense de Madrid, Facultad de Informática, leída el 23-01-2020Hoy en día la concurrencia y la distribución se han convertido en una parte fundamental del proceso de desarrollo de software. Indiscutiblemente, Internet y el uso cada vez más extendido de los procesadores multicore ha influido en el tipo de aplicaciones que se desarrollan. Esto ha dado lugar a la creación de distintos modelos de concurrencia .En particular, uno de los modelos de concurrencia que está ganando importancia es el modelo de objetos concurrentes basado en actores. En este modelo, los objetos (denominados actores) son las unidades de concurrencia. Cada objeto tiene su propio procesador y un estado local. La comunicación entre los mismos se lleva a cabo mediante el paso de mensajes. Cuando un objeto recibe un mensaje puede: actualizar su estado, mandar mensajes o crear nuevos objetos. Es bien sabido que la creación de programas concurrentes correctos es más compleja que la de programas secuenciales ya que es necesario tener en cuenta distintos aspectos inherentes a la concurrencia como los errores asociados a las carreras de datos o a los interbloqueos. Con el n de asegurar el correcto comportamiento de estos programas concurrentes se han desarrollado distintas técnicas de análisis estático y verificación para los diversos modelos de concurrencia existentes...Nowadays concurrency and distribution have become a fundamental part in the softwaredevelopment process. The Internet and the more extended use of multicore processorshave in uenced the type of the applications which are being developed. This has lead tothe creation of several concurrency models. In particular, a concurrency model that isgaining popularity is the actor model, the basis for concurrent objects. In this model,the objects (actors) are the concurrent units. Each object has its own processor and alocal state, and the communication between them is carried out using message passing.In response to receiving a message, an actor can update its local state, send messages orcreate new objects.Developing correct concurrent programs is known to be harder than writing sequentialones because of inherent aspects of concurrency such as data races or deadlocks. To ensurethe correct behavior of concurrent programs, static analyses and verication techniqueshave been developed for the diverse existent concurrency models...Fac. de InformáticaTRUEunpu