Special issue with selected papers from DISC 2009

This issue containsfivepapers selected among the thirty-three presented at the 23rd International Symposium on Distributed Computing (DISC 2009) in Elche, Spain. These five best papers were selected by the Program Committee. They are representative of the high quality research exhibited at DISC and of the topics covered therein. The papers appear here in revised and expanded form. The first two papers deal with agreement in asynchronous shared memory. This special issue begins with DISC’s Best Paper Award winner, The Disagreement Power of an Adversary by Delporte-Gallet, Fauconnier, Guerraoui, and Tielmann. While traditional work in the field assumes that up to some threshold, t , of processes may crash, this work considers adversaries that are not necessarily uniform, in the sense that they may crash certain combinations of processes and not others. There are 22 n such adversaries. In order to classify them, the paper introduces the notion of disagreement power: the biggest integer k for which the adversary can prevent processes from agreeing on k values. Using this notion, the authors show that there are in fact n equivalence classes of adversaries. A related paper is On Set Consensus Numbers by Gafni and Kuznetsov. It considers colorless tasks, in which a process is free to adopt the input or output value of any other participating process. The paper shows that any failure detector that solves a colorless task that cannot be solved k-resiliently also solves k-set consensus. More generally, it shows that every colorless task T can be characterized by its set consensus number: the largest k in {1, . . . , n} such that T is solvable