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Register a new userThe meaning of concurrent programs
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Added by
Victor Yodaiken
Publication date
2008
fields
Informatics Engineering
and research's language is
English
Authors
Victor Yodaiken
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The semantics of assignment and mutual exclusion in concurrent and multi-core/multi-processor systems is presented with attention to low level architectural features in an attempt to make the presentation realistic. Recursive functions on event sequences are used to define state dependent functions and variables in ordinary (non-formal-method) algebra.
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Concurrent Constraint Programming (CCP) is a declarative model for concurrency where agents interact by telling and asking constraints (pieces of information) in a shared store. Some previous works have developed (approximated) declarative debuggers for CCP languages. However, the task of debugging concurrent programs remains difficult. In this paper we define a dynamic slicer for CCP and we show it to be a useful companion tool for the existing debugging techniques. Our technique starts by considering a partial computation (a trace) that shows the presence of bugs. Often, the quantity of information in such a trace is overwhelming, and the user gets easily lost, since she cannot focus on the sources of the bugs. Our slicer allows for marking part of the state of the computation and assists the user to eliminate most of the redundant information in order to highlight the errors. We show that this technique can be tailored to timed variants of CCP. We also develop a prototypical implementation freely available for making experiments.
Programming is the activity of modifying a program in order to bring about specific changes in its behaviour. Yet programming language theory almost exclusively focuses on the meaning of programs. We motivate a change-oriented viewpoint from which the meaning of a program change is a change to the programs meaning.
Timed Concurrent Constraint Programming (tcc) is a declarative model for concurrency offering a logic for specifying reactive systems, i.e. systems that continuously interact with the environment. The universal tcc formalism (utcc) is an extension of tcc with the ability to express mobility. Here mobility is understood as communication of private names as typically done for mobile systems and security protocols. In this paper we consider the denotational semantics for tcc, and we extend it to a collecting semantics for utcc based on closure operators over sequences of constraints. Relying on this semantics, we formalize a general framework for data flow analyses of tcc and utcc programs by abstract interpretation techniques. The concrete and abstract semantics we propose are compositional, thus allowing us to reduce the complexity of data flow analyses. We show that our method is sound and parametric with respect to the abstract domain. Thus, different analyses can be performed by instantiating the framework. We illustrate how it is possible to reuse abstract domains previously defined for logic programming to perform, for instance, a groundness analysis for tcc programs. We show the applicability of this analysis in the context of reactive systems. Furthermore, we make also use of the abstract semantics to exhibit a secrecy flaw in a security protocol. We also show how it is possible to make an analysis which may show that tcc programs are suspension free. This can be useful for several purposes, such as for optimizing compilation or for debugging.
Frama-C is a software analysis framework that provides a common infrastructure and a common behavioral specification language to plugins that implement various static and dynamic analyses of C programs. Most plugins do not support concurrency. We have proposed Conc2Seq, a Frama-C plugin based on program transformation, capable to leverage the existing huge code base of plugins and to handle concurrent C programs. In this paper we formalize and sketch the proof of correctness of the program transformation principle behind Conc2Seq, and present an effort towards the full mechanization of both the formalization and proofs with the proof assistant Coq.
Strong adversaries obtain additional power when a linearizable object is substituted instead of an atomic object in a concurrent program. This paper suggests a novel approach to blunting this additional power, without relying on strongly linearizable implementations. Instead, a simple modification of some existing linearizable implementations is proposed with the property that if a concurrent program has non-zero termination probability when used with atomic objects, then it also has non-zero termination probability when it is used with the modified linearizable implementations. Our results apply to the ABD implementation of a shared register in asynchronous message-passing systems and also to AAD+ linearizable snapshots in asynchronous shared-memory systems.
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