In this paper we consider the mutual exclusion problem on a multiple access channel. Mutual exclusion is one of the fundamental problems in distributed computing. In the classic version of this problem, $n$ processes perform a concurrent program which occasionally triggers some of them to use shared resources, such as memory, communication channel, device, etc. The goal is to design a distributed algorithm to control entries and exits to/from the shared resource in such a way that in any time there is at most one process accessing it. We consider both the classic and a slightly weaker version of mutual exclusion, called $\ep$-mutual-exclusion, where for each period of a process staying in the critical section the probability that there is some other process in the critical section is at most $\ep$. We show that there are channel settings, where the classic mutual exclusion is not feasible even for randomized algorithms, while $\ep$-mutual-exclusion is. In more relaxed channel settings, we prove an exponential gap between the makespan complexity of the classic mutual exclusion problem and its weaker $\ep$-exclusion version. We also show how to guarantee fairness of mutual exclusion algorithms, i.e., that each process that wants to enter the critical section will eventually succeed.
@InProceedings{bienkowski_et_al:LIPIcs.STACS.2010.2446, author = {Bienkowski, Marcin and Klonowski, Marek and Korzeniowski, Miroslaw and Kowalski, Dariusz R.}, title = {{Dynamic Sharing of a Multiple Access Channel}}, booktitle = {27th International Symposium on Theoretical Aspects of Computer Science}, pages = {83--94}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-16-3}, ISSN = {1868-8969}, year = {2010}, volume = {5}, editor = {Marion, Jean-Yves and Schwentick, Thomas}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2010.2446}, URN = {urn:nbn:de:0030-drops-24467}, doi = {10.4230/LIPIcs.STACS.2010.2446}, annote = {Keywords: Distributed algorithms, multiple access channel, mutual exclusion} }
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