2,421 research outputs found
Stop It, and Be Stubborn!
A system is AG EF terminating, if and only if from every reachable state, a
terminal state is reachable. This publication argues that it is beneficial for
both catching non-progress errors and stubborn set state space reduction to try
to make verification models AG EF terminating. An incorrect mutual exclusion
algorithm is used as an example. The error does not manifest itself, unless the
first action of the customers is modelled differently from other actions. An
appropriate method is to add an alternative first action that models the
customer stopping for good. This method typically makes the model AG EF
terminating. If the model is AG EF terminating, then the basic strong stubborn
set method preserves safety and some progress properties without any additional
condition for solving the ignoring problem. Furthermore, whether the model is
AG EF terminating can be checked efficiently from the reduced state space
Verifying nondeterministic probabilistic channel systems against -regular linear-time properties
Lossy channel systems (LCSs) are systems of finite state automata that
communicate via unreliable unbounded fifo channels. In order to circumvent the
undecidability of model checking for nondeterministic
LCSs, probabilistic models have been introduced, where it can be decided
whether a linear-time property holds almost surely. However, such fully
probabilistic systems are not a faithful model of nondeterministic protocols.
We study a hybrid model for LCSs where losses of messages are seen as faults
occurring with some given probability, and where the internal behavior of the
system remains nondeterministic. Thus the semantics is in terms of
infinite-state Markov decision processes. The purpose of this article is to
discuss the decidability of linear-time properties formalized by formulas of
linear temporal logic (LTL). Our focus is on the qualitative setting where one
asks, e.g., whether a LTL-formula holds almost surely or with zero probability
(in case the formula describes the bad behaviors). Surprisingly, it turns out
that -- in contrast to finite-state Markov decision processes -- the
satisfaction relation for LTL formulas depends on the chosen type of schedulers
that resolve the nondeterminism. While all variants of the qualitative LTL
model checking problem for the full class of history-dependent schedulers are
undecidable, the same questions for finite-memory scheduler can be solved
algorithmically. However, the restriction to reachability properties and
special kinds of recurrent reachability properties yields decidable
verification problems for the full class of schedulers, which -- for this
restricted class of properties -- are as powerful as finite-memory schedulers,
or even a subclass of them.Comment: 39 page
Supporting Domain-Specific State Space Reductions through Local Partial-Order Reduction
Model checkers offer to automatically prove safety and liveness properties of complex concurrent software systems, but they are limited by state space explosion. Partial-Order Reduction (POR) is an effective technique to mitigate this burden. However, applying existing notions of POR requires to verify conditions based on execution paths of unbounded length, a difficult task in general. To enable a more intuitive and still flexible application of POR, we propose local POR (LPOR). LPOR is based on the existing notion of statically computed stubborn sets, but its locality allows to verify conditions in single states rather than over long paths. As a case study, we apply LPOR to message-passing systems. We implement it within the Java Pathfinder model checker using our general Java-based LPOR library. Our experiments show significant reductions achieved by LPOR for model checking representative message-passing protocols and, maybe surprisingly, that LPOR can outperform dynamic POR. © 2011 IEEE
Towards model checking electrum specifications with LTSmin
Dissertação de mestrado integrado em Engenharia InformáticaModel checking é uma técnica comum de verificação; garante a consistência e integridade de
qualquer sistema fazendo uma exploração exaustiva de todos os possíveis estados. Devido à
grande quantidade de intercalações possíveis entre eventos, modelos de sistemas distribuídos
muitas vezes acabam por gerar um número de estados muito grande. Nesta dissertação
vamos explorar os efeitos de partial order reduction — uma técnica para mitigar os efeitos
da explosão de estados — implementando uma linguagem semelhante ao Electrum com
LTSmin. Vamos também propor um event layer por cima do Electrum e uma análise sintática
para extrair informação necessária para que esta técnica possa ser implementada.Model checking is a common verification technique to guarantee the consistency and integrity
of any system by an exhaustive exploration of all possible states. Due to the large amount of
interleavings, models on distributed systems often end up with a huge state-space. In this
dissertation we will explore the effects of partial order reduction — a technique to mitigate
the effects of this state-explosion problem — by implementing an electrum-like language
with LTSmin. We will also propose an event layer over Electrum and a syntactic analysis to
extract valuable information for this technique to be implemented.This work is financed by the ERDF – European Regional Development Fund through
the Operational Programme for Competitiveness and Internationalisation - COMPETE 2020
Programme and by National Funds through the Portuguese funding agency, FCT - Fundação
para a Ciência e a Tecnologia, within project POCI-01-0145-FEDER-01682
Application of Partial-Order Methods to Reactive Systems with Event Memorization
International audienceWe are concerned in this paper with the verification of reactive systems with event memorization. The reactive systems are specified with an asynchronous reactive language Electre the main feature of which is the capability of memorizing occurrences of events in order to process them later. This memory capability is quite interesting for specifying reactive systems but leads to a verification model with a dramatically large number of states (due to the stored occurrences of events). In this paper, we show that partial-order methods can be applied successfuly for verification purposes on our model of reactive programs with event memorization. The main points of our work are two-fold: (1) we show that the independance relation which is a key point for applying partial-order methods can be extracted automatically from an \sf Electre program; (2) the partial-order technique turns out to be very efficient and may lead to a drastic reduction in the number of states of the model as demonstrated by a real-life industrial case study
Presentation of the 9th Edition of the Model Checking Contest.
International audience; The Model Checking Contest (MCC) is an annual competition of software tools for model checking. Tools must process an increasing benchmark gathered from the whole community and may participate in various examinations: state space generation, computation of global properties, computation of some upper bounds in the model, evaluation of reachability formulas, evaluation of CTL formulas, and evaluation of LTL formulas.For each examination and each model instance, participating tools are provided with up to 3600 s and 16 gigabyte of memory. Then, tool answers are analyzed and confronted to the results produced by other competing tools to detect diverging answers (which are quite rare at this stage of the competition, and lead to penalties).For each examination, golden, silver, and bronze medals are attributed to the three best tools. CPU usage and memory consumption are reported, which is also valuable information for tool developers
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