Fairness in systems based on multiparty interactions

In the context of the Multiparty Interaction Model, fairness is used to insure that an interaction that is enabled sufficiently often in a concurrent program will eventually be selected for execution. Unfortunately, this notion does not take conspiracies into account, i.e. situations in which an interaction never becomes enabled because of an unfortunate interleaving of independent actions; furthermore, eventual execution is usually too weak for practical purposes since this concept can only be used in the context of infinite executions. In this article, we present a new fairness notion, k-conspiracy-free fairness, that improves on others because it takes finite executions into account, alleviates conspiracies that are not inherent to a program, and k may be set a priori to control its goodness to address the above-mentioned problems.Ministerio de Ciencia y Tecnología TIC-2000-1106-C02-01Ministerio de Ciencia y Tecnología FIT-150100-2001-78Ministerio de Ciencia y Tecnología TAMANSI PCB-02-00

Generating non-conspiratorial executions

Avoiding conspiratorial executions is useful for debugging, model checking or refinement, and helps implement several wellknown problems in faulty environments; furthermore, avoiding non-equivalence robust executions prevents conflicting observations in a distributed setting from occurring. Our results prove that scheduling pairs of states and transitions in a strongly fair manner suf-fices to prevent conspiratorial executions; we then establish a formal connection between conspiracies and equivalence robustness; finally, we present a transformation scheme to implement our results and show how to build them into a well-known distributed scheduler. Previous results were applicable to a subset of systems only, just attempted to characterise potential conspiracies, or were tightly bound up with a particular interaction model.Comisión Interministerial de Ciencia y Tecnología TIC2003-02737-C0

An Algorithm for Ensuring Fairness and Liveness in Non-deterministic Systems Based on Multiparty Interactions

Strong fairness is a notion we can use to ensure that an element that is enabled infinitely often in a non–deterministic programme, will eventually be selected for execution so that it can progress. Unfortunately, “eventually” is too weak to induce the intuitive idea of liveliness and leads to anomalies that are not desirable, namely fair finiteness and conspiracies. In this paper, we focus on non–deterministic programmes based on multiparty interactions and we present a new criteria for selecting interactions called strong k–fairness that improves on other proposals in that it addresses both anomalies simultaneously, and k may be set a priori to control its goodness. We also show our notion is feasible, and present an algorithm for scheduling interactions in a strongly k–fair manner using a theoretical framework to support the multiparty interaction model. Our algorithm does not require to transform the source code to the processes that compose the system; furthermore, it can deal with both terminating and non–terminating processes.Comisión Interministerial de Ciencia y Tecnología TIC 2000–1106–C02–0

Liveliness and fairness in non-deterministic environments

El problema de la vivacidad y la selección justa surge en el contexto de los sistemas con ejecuciones no deterministas. El concepto de selección completamente justa ´ sirve para garantizar que todos los elementos que se habilitan infinitamente a menudo se ejecutan infinitamente a menudo. Esta noción de selección presenta dos anomalías: la finitud justa y las conspiraciones. Este articulo se centra en la selección justa de interacciones en sistemas basados en ´ interacciones entre múltiples participantes ´ y presenta una nueva noción llamada ´ selección completamente ´ k–justa cuya principal ventaja sobre otras propuestas es que da solución a las dos anomalías de forma simultanea. Para ello, hemos descrito un marco de trabajo teórico para caracterizar los sistemas ´ basados en interacciones entre múltiples participantes que hace independiente el criterio de selección del lenguaje de programación . También presentamos un algoritmo general para implementar ´ la selección completamente ´ k–justa de interacciones que no requiere acceder al estado local de los procesos del sistema.The problem of liveliness and fair selection arises in the context of systems with executing non-deterministic tions. The concept of completely fair selection serves to ensure that all items that are enabled infinitely often are executed infinitely often. This notion of selection presents two anomalies: fair finitude and conspiracies. East The article focuses on the fair selection of interactions in systems based on multi-participant interactions and introduces a new notion called completely k-fair selection. whose main advantage over other proposals is that it solves the two anomalies simultaneously. To do this, we have described a theoretical framework to characterize the systems based on interactions between multiple participants that makes the selection criteria independent tion of the programming language. We also present a general algorithm to implement the completely k-fair selection of interactions that does not require access to the local state of system processes

Vivacidad y justicia en entornos no deterministas

El problema de la vivacidad y la selección justa surge en el contexto de los sistemas con ejecuciones no determinadas. El concepto de selección completamente justa sirve para garantizar que todos los elementos  que se habilitan infinitamente a menudo se ejecutan infinitamente a menudo.Palabras clave: Sistema distribuidos, Interacciones entre múltiples participantes, vivacidad, selección justa

A review on DISC 2005, the 19th International Symposium on Distributed Computing

DISC is an international symposium on the theory, design, analysis, implementation and application of distributed systems and networks. The well-known International Symposium on Distributed Computing is organized annually in cooperation with the European Association for Theoretical Computer Science (EATCS). This is a review on the 19th International Symposium on Distributed Computing, which took place in Kraków, Poland, on September 26--29, 2005. The proceedings of DISC 2005 are published by Springer, as volume 3724 of the Lecture Notes in Computer Science (LNCS) series. The conference website can be found at www.mimuw.edu.pl/~disc2005.Postprint (published version

The Failure Detector Abstraction

This paper surveys the failure detector concept through two dimensions. First we study failure detectors as building blocks to simplify the design of reliable distributed algorithms. More specifically, we illustrate how failure detectors can factor out timing assumptions to detect failures in distributed agreement algorithms. Second, we study failure detectors as computability benchmarks. That is, we survey the weakest failure detector question and illustrate how failure detectors can be used to classify problems. We also highlights some limitations of the failure detector abstraction along each of the dimensions

An Abstract Framework for Deadlock Prevention in BIP

Part 6: Session 5: Model CheckingInternational audienceWe present a sound but incomplete criterion for checking deadlock freedom of finite state systems expressed in BIP: a component-based framework for the construction of complex distributed systems. Since deciding deadlock-freedom for finite-state concurrent systems is PSPACE-complete, our criterion gives up completeness in return for tractability of evaluation. Our criterion can be evaluated by model-checking subsystems of the overall large system. The size of these subsystems depends only on the local topology of direct interaction between components, and not on the number of components in the overall system. We present two experiments, in which our method compares favorably with existing approaches. For example, in verifying deadlock freedom of dining philosphers, our method shows linear increase in computation time with the number of philosophers, whereas other methods (even those that use abstraction) show super-linear increase, due to state-explosion