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On Asynchrony, Memory, and Communication: Separations and Landscapes

Authors Paola Flocchini , Nicola Santoro , Yuichi Sudo , Koichi Wada

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LIPIcs.OPODIS.2023.28.pdf
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Author Details

Paola Flocchini
  • EECS, University of Ottawa, Canada
Nicola Santoro
  • School of Computer Science, Carleton University, Ottawa, Canada
Yuichi Sudo
  • Faculty of Computer and Information Sciences, Hosei University, Tokyo, Japan
Koichi Wada
  • Faculty of Science and Engineering, Hosei University, Tokyo, Japan

Funding

This research was partly supported by NSERC through the Discovery Grant program, by JSPS KAKENHI No. 20H04140, 20KK0232, 20K11685, 21K11748, and by JST FOREST Program JPMJFR226U.

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Paola Flocchini, Nicola Santoro, Yuichi Sudo, and Koichi Wada. On Asynchrony, Memory, and Communication: Separations and Landscapes. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 28:1-28:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)
https://doi.org/10.4230/LIPIcs.OPODIS.2023.28

Abstract

Research on distributed computing by a team of identical mobile computational entities, called robots, operating in a Euclidean space in Look-Compute-Move (LCM) cycles, has recently focused on better understanding how the computational power of robots depends on the interplay between their internal capabilities (i.e., persistent memory, communication), captured by the four standard computational models (OBLOT, LUMI, FSTA, and FCOM) and the conditions imposed by the external environment, controlling the activation of the robots and their synchronization of their activities, perceived and modeled as an adversarial scheduler. We consider a set of adversarial asynchronous schedulers ranging from the classical semi-synchronous (Ssynch) and fully asynchronous (Asynch) settings, including schedulers (emerging when studying the atomicity of the combination of operations in the LCM cycles) whose adversarial power is in between those two. We ask the question: what is the computational relationship between a model M₁ under adversarial scheduler K₁ (M₁(K₁)) and a model M₂ under scheduler K₂ (M₂(K₂))? For example, are the robots in M₁(K₁) more powerful (i.e., they can solve more problems) than those in M₂(K₂)? We answer all these questions by providing, through cross-model analysis, a complete characterization of the computational relationship between the power of the four models of robots under the considered asynchronous schedulers. In this process, we also provide qualified answers to several open questions, including the outstanding one on the proper dominance of Ssynch over Asynch in the case of unrestricted visibility.

Subject Classification

ACM Subject Classification
  • Theory of computation → Distributed algorithms
Keywords
  • Look-Compute-Move
  • Oblivious mobile robots
  • Robots with lights
  • Memory versus Communication
  • Moving and Computing
  • Asynchrony

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