A Wealth of Sub-Consensus Deterministic Objects

Authors Eli Daian, Giuliano Losa, Yehuda Afek, Eli Gafni



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Author Details

Eli Daian
  • School of Computer Science, Tel-Aviv University, Israel
Giuliano Losa
  • Computer Science Department, University of California, Los Angeles, CA, USA
Yehuda Afek
  • School of Computer Science, Tel-Aviv University, Israel
Eli Gafni
  • Computer Science Department, University of California, Los Angeles, CA, USA

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Eli Daian, Giuliano Losa, Yehuda Afek, and Eli Gafni. A Wealth of Sub-Consensus Deterministic Objects. In 32nd International Symposium on Distributed Computing (DISC 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 121, pp. 17:1-17:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018) https://doi.org/10.4230/LIPIcs.DISC.2018.17

Abstract

The consensus hierarchy classifies shared an object according to its consensus number, which is the maximum number of processes that can solve consensus wait-free using the object. The question of whether this hierarchy is precise enough to fully characterize the synchronization power of deterministic shared objects was open until 2016, when Afek et al. showed that there is an infinite hierarchy of deterministic objects, each weaker than the next, which is strictly between i and i+1-processors consensus, for i >= 2. For i=1, the question whether there exist a deterministic object whose power is strictly between read-write and 2-processors consensus, remained open.
We resolve the question positively by exhibiting an infinite hierarchy of simple deterministic objects which are equivalent to set-consensus tasks, and thus are stronger than read-write registers, but they cannot implement consensus for two processes. Still our paper leaves a gap with open questions.

Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed computing models
Keywords
  • shared memory
  • distributed algorithms
  • wait-free
  • set consensus

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References

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