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Documents authored by Johnen, Colette

Document
DOI: 10.4230/LIPIcs.STACS.2025.30
Being Efficient in Time, Space, and Workload: a Self-Stabilizing Unison and Its Consequences

Authors: Stéphane Devismes, David Ilcinkas, Colette Johnen, and Frédéric Mazoit

Published in: LIPIcs, Volume 327, 42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)

Abstract
We present a self-stabilizing algorithm for the unison problem which is efficient in time, workload, and space in a weak model. Precisely, our algorithm is defined in the atomic-state model and works in anonymous asynchronous connected networks in which even local ports are unlabeled. It makes no assumption on the daemon and thus stabilizes under the weakest one: the distributed unfair daemon. In an n-node network of diameter D and assuming the knowledge B ≥ 2D+2, our algorithm only requires Θ(log(B)) bits per node and is fully polynomial as it stabilizes in at most 2D+2 rounds and O(min(n²B, n³)) moves. In particular, it is the first self-stabilizing unison for arbitrary asynchronous anonymous networks achieving an asymptotically optimal stabilization time in rounds using a bounded memory at each node. Furthermore, we show that our solution can be used to efficiently simulate synchronous self-stabilizing algorithms in asynchronous environments. For example, this simulation allows us to design a new state-of-the-art algorithm solving both the leader election and the BFS (Breadth-First Search) spanning tree construction in any identified connected network which, to the best of our knowledge, beats all existing solutions in the literature.
Cite as

Stéphane Devismes, David Ilcinkas, Colette Johnen, and Frédéric Mazoit. Being Efficient in Time, Space, and Workload: a Self-Stabilizing Unison and Its Consequences. In 42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 327, pp. 30:1-30:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{devismes_et_al:LIPIcs.STACS.2025.30,
  author =	{Devismes, St\'{e}phane and Ilcinkas, David and Johnen, Colette and Mazoit, Fr\'{e}d\'{e}ric},
  title =	{{Being Efficient in Time, Space, and Workload: a Self-Stabilizing Unison and Its Consequences}},
  booktitle =	{42nd International Symposium on Theoretical Aspects of Computer Science (STACS 2025)},
  pages =	{30:1--30:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-365-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{327},
  editor =	{Beyersdorff, Olaf and Pilipczuk, Micha{\l} and Pimentel, Elaine and Thắng, Nguy\~{ê}n Kim},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2025.30},
  URN =		{urn:nbn:de:0030-drops-228568},
  doi =		{10.4230/LIPIcs.STACS.2025.30},
  annote =	{Keywords: Self-stabilization, unison, time complexity, synchronizer}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.4
Efficient Wait-Free Queue Algorithms with Multiple Enqueuers and Multiple Dequeuers

Authors: Colette Johnen, Adnane Khattabi, and Alessia Milani

Published in: LIPIcs, Volume 253, 26th International Conference on Principles of Distributed Systems (OPODIS 2022)

Abstract
Despite the widespread usage of FIFO queues in distributed applications, designing efficient wait-free implementations of queues remains a challenge. The majority of wait-free queue implementations restrict either the number of dequeuers or the number of enqueuers that can operate on the queue, even when they use strong synchronization primitives, like the Compare&Swap. If we do not limit the number of processes that can perform enqueue and dequeue operations, the best-known upper bound on the worst case step complexity for a wait-free queue is given by [Khanchandani and Wattenhofer, 2018]. In particular, they present an implementation of a multiple dequeuer multiple enqueuer wait-free queue whose worst case step complexity is in O(√n), where n is the number of processes. In this work, we investigate whether it is possible to improve this bound. In particular, we present a wait-free FIFO queue implementation that supports n enqueuers and k dequeuers where the worst case step complexity of an Enqueue operation is in O(log n) and of a Dequeue operation is in O(k log n). Then, we show that if the semantics of the queue can be relaxed, by allowing concurrent Dequeue operations to retrieve the same element, then we can achieve O(log n) worst-case step complexity for both the Enqueue and Dequeue operations.
Cite as

Colette Johnen, Adnane Khattabi, and Alessia Milani. Efficient Wait-Free Queue Algorithms with Multiple Enqueuers and Multiple Dequeuers. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 4:1-4:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{johnen_et_al:LIPIcs.OPODIS.2022.4,
  author =	{Johnen, Colette and Khattabi, Adnane and Milani, Alessia},
  title =	{{Efficient Wait-Free Queue Algorithms with Multiple Enqueuers and Multiple Dequeuers}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{4:1--4:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-265-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{253},
  editor =	{Hillel, Eshcar and Palmieri, Roberto and Rivi\`{e}re, Etienne},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2022.4},
  URN =		{urn:nbn:de:0030-drops-176240},
  doi =		{10.4230/LIPIcs.OPODIS.2022.4},
  annote =	{Keywords: Distributed computing, distributed algorithms, FIFO queue, shared memory, fault tolerance, concurrent data structures, relaxed specifications, complexity}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2016.10
Self-Stabilizing Disconnected Components Detection and Rooted Shortest-Path Tree Maintenance in Polynomial Steps

Authors: Stéphane Devismes, David Ilcinkas, and Colette Johnen

Published in: LIPIcs, Volume 70, 20th International Conference on Principles of Distributed Systems (OPODIS 2016)

Abstract
We deal with the problem of maintaining a shortest-path tree rooted at some process r in a network that may be disconnected after topological changes. The goal is then to maintain a shortest-path tree rooted at r in its connected component, V_r, and make all processes of other components detecting that r is not part of their connected component. We propose, in the composite atomicity model, a silent self-stabilizing algorithm for this problem working in semi-anonymous networks under the distributed unfair daemon (the most general daemon) without requiring any a priori knowledge about global parameters of the network. This is the first algorithm for this problem that is proven to achieve a polynomial stabilization time in steps. Namely, we exhibit a bound in O(W_{max} * n_{maxCC}^3 * n), where W_{max} is the maximum weight of an edge, n_{maxCC} is the maximum number of non-root processes in a connected component, and n is the number of processes. The stabilization time in rounds is at most 3n_{maxCC} + D, where D is the hop-diameter of V_r.
Cite as

Stéphane Devismes, David Ilcinkas, and Colette Johnen. Self-Stabilizing Disconnected Components Detection and Rooted Shortest-Path Tree Maintenance in Polynomial Steps. In 20th International Conference on Principles of Distributed Systems (OPODIS 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 70, pp. 10:1-10:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{devismes_et_al:LIPIcs.OPODIS.2016.10,
  author =	{Devismes, St\'{e}phane and Ilcinkas, David and Johnen, Colette},
  title =	{{Self-Stabilizing Disconnected Components Detection and Rooted Shortest-Path Tree Maintenance in Polynomial Steps}},
  booktitle =	{20th International Conference on Principles of Distributed Systems (OPODIS 2016)},
  pages =	{10:1--10:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-031-6},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{70},
  editor =	{Fatourou, Panagiota and Jim\'{e}nez, Ernesto and Pedone, Fernando},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2016.10},
  URN =		{urn:nbn:de:0030-drops-70792},
  doi =		{10.4230/LIPIcs.OPODIS.2016.10},
  annote =	{Keywords: distributed algorithm, self-stabilization, routing algorithm, shortest path, disconnected network, shortest-path tree}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2015.12
On the Uncontended Complexity of Anonymous Consensus

Authors: Claire Capdevielle, Colette Johnen, Petr Kuznetsov, and Alessia Milani

Published in: LIPIcs, Volume 46, 19th International Conference on Principles of Distributed Systems (OPODIS 2015)

Abstract
Consensus is one of the central distributed abstractions. By enabling a collection of processes to agree on one of the values they propose, consensus can be used to implement any generic replicated service in a consistent and fault-tolerant way. In this paper, we study uncontended complexity of anonymous consensus algorithms, counting the number of memory locations used and the number of memory updates performed in operations that encounter no contention. We assume that contention-free operations on a consensus object perform "fast" reads and writes, and resort to more expensive synchronization primitives, such as CAS, only when contention is detected. We call such concurrent implementations interval-solo-fast and derive one of the first nontrivial tight bounds on space complexity of anonymous interval-solo-fast consensus.
Cite as

Claire Capdevielle, Colette Johnen, Petr Kuznetsov, and Alessia Milani. On the Uncontended Complexity of Anonymous Consensus. In 19th International Conference on Principles of Distributed Systems (OPODIS 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 46, pp. 12:1-12:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{capdevielle_et_al:LIPIcs.OPODIS.2015.12,
  author =	{Capdevielle, Claire and Johnen, Colette and Kuznetsov, Petr and Milani, Alessia},
  title =	{{On the Uncontended Complexity of Anonymous Consensus}},
  booktitle =	{19th International Conference on Principles of Distributed Systems (OPODIS 2015)},
  pages =	{12:1--12:16},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-939897-98-9},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{46},
  editor =	{Anceaume, Emmanuelle and Cachin, Christian and Potop-Butucaru, Maria},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2015.12},
  URN =		{urn:nbn:de:0030-drops-66034},
  doi =		{10.4230/LIPIcs.OPODIS.2015.12},
  annote =	{Keywords: space and time complexity, lower bounds, consensus, interval contention, solo-fast}
}
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