Distributed Universality: Contention-Awareness, Wait-freedom, Object Progress, and Other Properties

A notion of a universal construction suited to distributed computing has been introduced by M. Herlihy in his celebrated paper "Wait-free synchronization" (ACM TOPLAS, 1991). A universal construction is an algorithm that can be used to wait-free implement any object defined by a sequential specification. Herlihy's paper shows that the basic system model, which supports only atomic read/write registers, has to be enriched with consensus objects to allow the design of universal constructions. The generalized notion of a k-universal construction has been recently introduced by Gafni and Guerraoui (CONCUR, 2011). A k-universal construction is an algorithm that can be used to simultaneously implement k objects (instead of just one object), with the guarantee that at least one of the k constructed objects progresses forever. While Herlihy's universal construction relies on atomic registers and consensus objects, a k-universal construction relies on atomic registers and k-simultaneous consensus objects (which are wait-free equivalent to k-set agreement objects in the read/write system model). This paper significantly extends the universality results introduced by Herlihy and Gafni-Guerraoui. In particular, we present a k-universal construction which satisfies the following five desired properties, which are not satisfied by the previous k-universal construction: (1) among the k objects that are constructed, at least l objects (and not just one) are guaranteed to progress forever; (2) the progress condition for processes is wait-freedom, which means that each correct process executes an infinite number of operations on each object that progresses forever; (3) if any of the k constructed objects stops progressing, all its copies (one at each process) stop in the same state; (4) the proposed construction is contention-aware, in the sense that it uses only read/write registers in the absence of contention; and (5) it is generous with respect to the obstruction-freedom progress condition, which means that each process is able to complete any one of its pending operations on the k objects if all the other processes hold still long enough. The proposed construction, which is based on new design principles, is called a (k, l)-universal construction. It uses a natural extension of k-simultaneous consensus objects, called (k, l)-simultaneous consensus objects ((k, l)-SC). Together with atomic registers, (k, l)-SC objects are shown to be necessary and sufficient for building a (k, l)-universal construction, and, in that sense, (k, l)-SC objects are (k, l)-universal.Cet article explore la notion de construction universelle dans les systèmes distribués. Il présente une construction k-universelle wait-free qui s'adapte à la concurrence à partir d'objets k-consensus

Migration Needs Global Regulation

1People Flow proposes a regulatory system that is nationalist and discriminatory. Instead we need a global system of regulation based on the principles of free movement and universal justice.openopenR. MARCHETTIMarchetti, Raffael

Read-Write Memory and k-Set Consensus as an Affine Task

The wait-free read-write memory model has been characterized as an iterated \emph{Immediate Snapshot} (IS) task. The IS task is \emph{affine}---it can be defined as a (sub)set of simplices of the standard chromatic subdivision. It is known that the task of \emph{Weak Symmetry Breaking} (WSB) cannot be represented as an affine task. In this paper, we highlight the phenomenon of a "natural" model that can be captured by an iterated affine task and, thus, by a subset of runs of the iterated immediate snapshot model. We show that the read-write memory model in which, additionally, $k$-set-consensus objects can be used is, unlike WSB, "natural" by presenting the corresponding simple affine task captured by a subset of $2$-round IS runs. Our results imply the first combinatorial characterization of models equipped with abstractions other than read-write memory that applies to generic tasks

A Look at Basics of Distributed Computing *

International audienceThis paper presents concepts and basics of distributed computing which are important (at least from the author's point of view), and should be known and mastered by Master students and engineers. Those include: (a) a characterization of distributed computing (which is too much often confused with parallel computing); (b) the notion of a synchronous system and its associated notions of a local algorithm and message adversaries; (c) the notion of an asynchronous shared memory system and its associated notions of universality and progress conditions; and (d) the notion of an asynchronous message-passing system with its associated broadcast and agreement abstractions, its impossibility results, and approaches to circumvent them. Hence, the paper can be seen as a guided tour to key elements that constitute basics of distributed computing

The problem of subsumption in Kant, Hegel and Marx

This thesis explores the concept of subsumption in the work of Immanuel Kant, G.W.F. Hegel and Karl Marx in order to construct a distinct theoretical problem resting on the articulation of conceptual and social relations. Each of these authors develops a ‘logic’ within which subsumptive relations are operative: Transcendental logic, dialectical logic and finally Marx’s ‘logic of the body politic’; these are investigated in turn. The thesis opens with a close reading of subsumption in Kant’s philosophy, arguing that it is here that the concept first attains its modern or critical sense. This critical sense distinguishes it from the classical notion of subsumption (as a formal or purely logical relation) and gives rise to a novel philosophical account of how synthetic subsumption acts unite heterogeneous elements within a compositional totality. In Hegel’s philosophy this account takes on a series of new determinations, as social, historical and developmental aspects to subsumption are introduced. Nonetheless, Hegel’s concept of subsumption remains within the ambit of a ‘closed’ idealist discourse, just as Kant’s does. The second section of the thesis explores how this closure is thrown into crisis by Marx’s materialist attack on philosophy as a self-sufficient branch of knowledge, altering the stakes of conceptual relations as such, and therefore subsumption. Drawing on the work of Mexican-Ecuadoran philosopher Bolívar Echeverría, Marx’s materialism is reconstructed as a theory of social reproduction, encompassing the practical process of social life in its entirety. This then provides the basis for an analysis of subsumption in its specifically capitalist form, which, the thesis argues, must be thought as operative at three levels of social activity: exchange, production and reproduction, each with their own distinct but interconnected logics of power and resistance. Grasping these three dimensions in their unity, the thesis finally outlines an original framework for comprehending capitalist domination in its concrete specificity. In order to do so it goes beyond Marx’s own theory of (formal and real) subsumption as well as interpretations of it that reinstate theoretical closure to historical contingency (for example in the work of Negri and Adorno). Instead, a dynamic theory of capitalist subsumption is proposed in order to register the diverse mechanisms of control through which capitalist power shapes the course of social reproduction and historical development

Distributed Universality

International audienceA notion of a universal construction suited to distributed computing has been introduced by M. Herlihy in his celebrated paper “Wait-free synchronization” (ACM TOPLAS, 1991). A universal construction is an algorithm that can be used to wait-free implement any object defined by a sequential specification. Herlihy’s paper shows that the basic system model, which supports only atomic read/write registers, has to be enriched with consensus objects to allow the design of universal constructions. The generalized notion of a k-universal construction has been recently introduced by Gafni and Guerraoui (CONCUR, 2011). A k-universal construction is an algorithm that can be used to simultaneously implement k objects (instead of just one object), with the guarantee that at least one of the k constructed objects progresses forever. While Herlihy’s universal construction relies on atomic registers and consensus objects, a k-universal construction relies on atomic registers and k-simultaneous consensus objects (which are wait-free equivalent to k-set agreement objects in the read/write system model).This paper significantly extends the universality results introduced by Herlihy and Gafni-Guerraoui. In particular, we present a k-universal construction which satisfies the following five desired properties, which are not satisfied by the previous k-universal construction: (1) among the k objects that are constructed, at least ℓ objects (and not just one) are guaranteed to progress forever; (2) the progress condition for processes is wait-freedom, which means that each correct process executes an infinite number of operations on each object that progresses forever; (3) if any of the k constructed objects stops progressing, all its copies (one at each process) stop in the same state; (4) the proposed construction is contention-aware, in the sense that it uses only read/write registers in the absence of contention; and (5) it is generous with respect to the obstruction-freedom progress condition, which means that each process is able to complete any one of its pending operations on the k objects if all the other processes hold still long enough. The proposed construction, which is based on new design principles, is called a (k,ℓ)-universal construction. It uses a natural extension of k-simultaneous consensus objects, called (k,ℓ)-simultaneous consensus objects ((k,ℓ)-SC). Together with atomic registers, (k,ℓ)-SC objects are shown to be necessary and sufficient for building a (k,ℓ)-universal construction, and, in that sense, (k,ℓ)-SC objects are (k,ℓ)-universal

Brief announcement: distributed universality: contention-awareness; wait-freedom; object progress, and other properties

International audienceA notion of a universal construction suited to distributed computing has been introduced by M. Herlihy in his celebrated paper "Wait-free synchronization" (ACM TOPLAS, 1991). A universal construction is an algorithm that can be used to wait-free implement any object defined by a sequential specification. Herlihy's paper shows that the basic system model, which supports only atomic read/write registers, has to be enriched with consensus objects to allow the design of universal constructions.The generalized notion of a k-universal construction has been recently introduced by Gafni and Guerraoui (CONCUR, 2011). A k-universal construction is an algorithm that can be used to simultaneously implement k objects (instead of just one object), with the guarantee that at least one of the k constructed objects progresses forever. While Herlihy's universal construction relies on atomic registers and consensus objects, a k-universal construction relies on atomic registers and k-simultaneous consensus objects (which have been shown to be computationally equivalent to k-set agreement objects in the read/write system model where any number of processes may crash).This paper significantly extends the universality results introduced by Herlihy and Gafni-Guerraoui. In particular, we present a k-universal construction which satisfies the following five desired properties, which are not satisfied by the previous k-universal construction: (1) among the k objects that are constructed, at least l objects (and not just one) are guaranteed to progress forever; (2) the progress condition for processes is wait-freedom, which means that each correct process executes an infinite number of operations on each object that progresses forever; (3) if one of the k constructed objects stops progressing, it stops in the same state at each process; (4) the proposed construction is contention-aware, which means that it uses only read/write registers in the absence of contention; and (5) it is indulgent with respect to the obstruction-freedom progress condition, which means that each process is able to complete any one of its pending operations on the k objects if all the other process hold still long enough.The proposed construction, which is based on new design principles, is called a (k,l)-universal construction. It uses a natural extension of k-simultaneous consensus objects, called (k,l)-simultaneous consensus objects ((k,l)-SC). Together with atomic registers, (k,l)-SC objects are shown to be necessary and sufficient for building a (k,l)-universal construction, and, in that sense, (k,l)-SC objects are (k,l)-universal