Construction méthodique d'un algorithme réparti de détection de la terminaison

Disponible dans les fichiers attachés à ce documen

Consensus in Byzantine asynchronous systems

AbstractThis paper presents a consensus protocol resilient to Byzantine failures. It uses signed and certified messages and is based on two underlying failure detection modules. The first is a muteness failure detection module of the class ♢M. The second is a reliable Byzantine behaviour detection module. More precisely, the first module detects processes that stop sending messages, while processes experiencing other non-correct behaviours (i.e., Byzantine) are detected by the second module. The protocol is resilient to F faulty processes, F⩽min(⌊(n−1)/2⌋,C) (where C is the maximum number of faulty processes that can be tolerated by the underlying certification service).The approach used to design the protocol is new. While usual Byzantine consensus protocols are based on failure detectors to detect processes that stop communicating, none of them use a module to detect their Byzantine behaviour (this detection is not isolated from the protocol and makes it difficult to understand and prove correct). In addition to this modular approach and to a consensus protocol for Byzantine systems, the paper presents a finite state automaton-based implementation of the Byzantine behaviour detection module. Finally, the modular approach followed in this paper can be used to solve other problems in asynchronous systems experiencing Byzantine failures

About the efficiency of partial replication to implement Distributed Shared Memory

Distributed Shared Memory abstraction (DSM) is traditionally realized through a distributed memory consistency system(MCS) on top of a message passing system. In this paper we analyze the impossibility of efficient partial replication implementation of causally consistent DSM. Efficiency is discussed in terms of control information that processes have to propagate to maintain consistency. We introduce the notions of share graph and hoop to model variable distribution and the concept of dependency chain to characterize processes that have to manage information about a variable even though they do not read or write that variable. Then, we weaken causal consistency to try to define new consistency criteria weaker enough to allow efficient partial replication implementations and strong enough to solve interesting problems. Finally, we prove that PRAM is such a criterion, and illustrate its power with the Bellman-Ford shortest path algorithm. / Les mémoires partagées réparties constituent une abstraction qui est traditionellement concrétisée par un système réparti de mémoire cohérente, au-dessus d'un système de communication par messages. Dans ce rapport, on analyse l'impossibilité d'avoir une implémentation efficace de mémoire partagée répartie à cohérence causale, basée sur la duplication partielle des variables. L'efficacité est envisagée en terme d'information contrôle qui doit être propagée pour assurer la cohérence. On introduit les notions de graphe de partage et d'arceau, qui modélisent la répartition des variables et la notion de chaîne de dépendance pour caractériser les processus qui doivent gérer des informations relatives à une variable dont ils ne possèdent pas de copie locale. Ensuite, on affaiblit le critère de cohérence causale, dans le but de déterminer un nouveau critère de cohérence qui soit suffisament faible pour permettre un implémentation efficace basée sur la duplication partielle, mais suffisament forte pour pouvoir résoudre des problèmes intéressants. Finalement, on prouve que le critère appelé PRAM satisfait ces exigences, et illustrons sa pertinence en montrant une implémentation de l'algorithme de plus court chemin de Bellman-Ford

Controler les transferts de connaissance dans les algorithmes distribués.Application à la détection de l'interblocage

Disponible dans les fichiers attachés à ce documen

Déterminer un état global

Le calcul d'un état global d'un système réparti est l'un des paradigmes des problèmes de contrôle réparti. Apres avoir exposé le problème, cet article en analyse et présente plusieurs solutions. Celles-ci se distinguent les unes des autres par les hypothèses qu'elles font sur les canaux de communication et les messages de contrôle utilisés. En plus de son caractère "synthétique" sur le calcul d'un état global réparti, cet article illustre de nombreuses hypothèses (et difficultés) propres au contexte réparti

Deadlock models and general algorithm for distributed deadlock detection

Disponible dans les fichiers attachés à ce documen

Computing Global Functions in Asynchronous Distributed Systems with Process Crashes

Disponible dans les fichiers attachés à ce documen

255 In vivo detection of non-occlusive thrombi in drug-eluting stents by scintigraphy and radio-labelled annexin V in a rabbit model

IntroductionThrombi in contact with non re-endothelialized stent struts associated with drug-eluting stent (DES) thrombosis. Hence, detection of thrombi in DES could help to evaluate the risk of DES thrombosis. Annexin V radio-labelled with 99mTechnetium (99mTc) is a radio-tracer with a high affinity for activated platelets.ObjectivesOur objectives were: 1) to develop an animal model of non-occlusive thrombosis of stents, 2) to evaluate the ability of annexin V 99mTc for the detection of in-stent thrombi using scintigraphy.MethodsRight carotid arteries of NZW rabbits (n=14) fed a high cholesterol diet were implanted with overlapping DES (n=7) or bare-metal stents (BMS; n=7). Four weeks after stent implantation, rabbits underwent a first scintigraphy 3 hours after injection of 200 MBq of radio-labelled annexin V 99mTc. At the end of the first scintigraphy, a suture was placed surgically proximal to the stented carotid arteries in order to induce a thrombus-prone flow limiting stenosis. Four days later, a second scintigraphy was performed. After the second scintigraphy, stents were excised, imaged ex vivo and then fixed for histological examination and scanning electron microscopy (SEM).ResultsActivities measured in vivo in the stented carotid arteries after injection of annexin V 99mTc were higher on the second scintigraphy after creation of a surgical stenosis as compared to the first scintigraphy (0.24 vs. 0.15 counts/pixel/MBq, respectively; p<0.05). On the second scintigraphy, activities were higher in DES vs. BMS (0.26 vs. 0.19 counts/pixel/MBq, respectively; p < 0.005). High activities measured in stents in vivo were associated with the detection of thrombi on corresponding histological sections and SEM.ConclusionsIn this work, we developed a rabbit model of non-occlusive thrombosis of stents in carotid arteries. In this model, in-stent thrombi could be detected using annexin V 99mTc scintigraphy

Observing global states of asynchronous distributed applications

Disponible dans les fichiers attachés à ce documen