Reversibility in session-based concurrency: A fresh look

Much research has studied foundations for correct and reliable communication-centric software systems. A salient approach to correctness uses verification based on session types to enforce structured communications; a recent approach to reliability uses reversible actions as a way of reacting to unanticipated events or failures. In this paper, we develop a simple observation: the semantic machinery required to define asynchronous (queue-based), monitored communications can also support reversible protocols. We propose a framework of session communication in which monitors support reversibility of (untyped) processes. Main novelty in our approach are session types with present and past, which allow us to streamline the semantics of reversible actions. We prove that reversibility in our framework is causally consistent, and define ways of using monitors to control reversible actions. Keyword

Generation de une sémantique reversible pour Erlang en Maude

In recent years, reversibility in concurrent settings has attracted interest thanks to its diverse applications in areas such as error recovery, debugging, and biological modeling. Also, it has been studied in many formalisms, including Petri nets, process algebras, and programming languages like Erlang. However, most attempts made so far suffer from the same limitation: they define their reversible semantics in an ad-hoc fashion. To address this limit, Lanese et al. have recently proposed a novel general method to derive a concurrent reversible semantics from a non-reversible one. However, in most interesting instances the method relies on infinite sets of reductions, making doubtful its practical usability. We bridge the gap between theory and practice by implementing it in Maude. The key insight is that infinite sets of reductions can be captured by a small number of schemas in many relevant cases. This happens indeed for our application: the functional and concurrent fragment of Erlang. We extend the framework with a general rollback operator, allowing one to undo an action far in the past, including all and only its consequences. We can thus use our framework, e.g., as an oracle against which to test the reversible debugger CauDEr for Erlang, or as an executable specification for new reversible debuggers.Récemment, la réversibilité dans les systèmes concurrents a été mise à profit dans plusieurs applications tirées de domaines différents comme le débogage, la reprise sur erreurs et la modélisation des systèmes biologiques. La réversibilité a été étudiée dans plusieurs formalismes, comme les réseaux de Petri, les algèbres de processus et différents langages de programmation. Néanmoins, tous les travaux visant à développer une variante réversibles de ces formalismes souffrent de la même limitation: les sémantiques ont toujours été définies de manière ad-hoc. Très récemment, Lanese et al. ont proposé une méthode générale pour définir une sémantique réversible concurrente, de manière automatique, à partir d'une sémantique opérationnelle non réversible. Cette méthode n'avait cependant pas été instrumentée. Le but de ce papier est d'en proposer une implantation, prouvée correcte, dans l'environnement de logique de réécriture Maude, et de l'appliquer à un cas d'étude: le langage de programmation Erlang

Controlled reversibility and compensations

In this paper we report the main ideas of an ongoing thread of research that aims at exploiting reversibility mechanisms to define programming abstractions for dependable distributed systems. In particular, we discuss the issues posed by concurrency in the definition of controlled forms of reversibility. We also discuss the need of introducing compensations to deal with irreversible actions and to avoid to repeat past errors