82 Search Results for "Attiya, Hagit"

Volume

LIPIcs, Volume 179

34th International Symposium on Distributed Computing (DISC 2020)

DISC 2020, October 12-16, 2020, Virtual Conference

Editors: Hagit Attiya

Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2024.42
Brief Announcement: Solvability of Three-Process General Tasks

Authors: Hagit Attiya, Pierre Fraigniaud, Ami Paz, and Sergio Rajsbaum

Published in: LIPIcs, Volume 319, 38th International Symposium on Distributed Computing (DISC 2024)

Abstract
The topological view on distributed computing represents a task T as a relation Δ between the complex ℐ of its inputs and the complex 𝒪 of its outputs. A cornerstone result in the field is an elegant computability characterization of the solvability of colorless tasks in terms of ℐ, 𝒪 and Δ. Essentially, a colorless task is wait-free solvable if and only if there is a continuous map from the geometric realization of ℐ to that of 𝒪 that respects Δ. This paper makes headway towards providing an analogous characterization for general tasks, which are not necessarily colorless, by concentrating on the case of three-process inputless tasks. Our key contribution is identifying local articulation points as an obstacle for the solvability of general tasks, and defining a topological deformation on the output complex of a task T, which eliminates these points by splitting them, to obtain a new task T', with an adjusted relation Δ' between the input complex ℐ and an output complex 𝒪' without articulation points. We obtain a new characterization of wait-free solvability of three-process general tasks: T is wait-free solvable if and only if there is a continuous map from the geometric realization of ℐ to that of 𝒪' that respects Δ'.
Cite as

Hagit Attiya, Pierre Fraigniaud, Ami Paz, and Sergio Rajsbaum. Brief Announcement: Solvability of Three-Process General Tasks. In 38th International Symposium on Distributed Computing (DISC 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 319, pp. 42:1-42:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{attiya_et_al:LIPIcs.DISC.2024.42,
  author =	{Attiya, Hagit and Fraigniaud, Pierre and Paz, Ami and Rajsbaum, Sergio},
  title =	{{Brief Announcement: Solvability of Three-Process General Tasks}},
  booktitle =	{38th International Symposium on Distributed Computing (DISC 2024)},
  pages =	{42:1--42:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-352-2},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{319},
  editor =	{Alistarh, Dan},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2024.42},
  URN =		{urn:nbn:de:0030-drops-212700},
  doi =		{10.4230/LIPIcs.DISC.2024.42},
  annote =	{Keywords: Wait-free computing, lower bounds, topology}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.4
The Synchronization Power of Auditable Registers

Authors: Hagit Attiya, Antonella Del Pozzo, Alessia Milani, Ulysse Pavloff, and Alexandre Rapetti

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
Auditability allows to track all the read operations performed on a register. It abstracts the need of data owners to control access to their data, tracking who read which information. This work considers possible formalizations of auditing and their ramification for the possibility of providing it. The natural definition is to require a linearization of all write, read and audit operations together (atomic auditing). The paper shows that atomic auditing is a powerful tool, as it can be used to solve consensus. The number of processes that can solve consensus using atomic audit depends on the number of processes that can read or audit the register. If there is a single reader or a single auditor (the writer), then consensus can be solved among two processes. If multiple readers and auditors are possible, then consensus can be solved among the same number of processes. This means that strong synchronization primitives are needed to support atomic auditing. We give implementations of atomic audit when there are either multiple readers or multiple auditors (but not both) using primitives with consensus number 2 (swap and fetch&add). When there are multiple readers and multiple auditors, the implementation uses compare&swap. These findings motivate a weaker definition, in which audit operations are not linearized together with read and write operations (regular auditing). We prove that regular auditing can be implemented from ordinary reads and writes on atomic registers.
Cite as

Hagit Attiya, Antonella Del Pozzo, Alessia Milani, Ulysse Pavloff, and Alexandre Rapetti. The Synchronization Power of Auditable Registers. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 4:1-4:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{attiya_et_al:LIPIcs.OPODIS.2023.4,
  author =	{Attiya, Hagit and Del Pozzo, Antonella and Milani, Alessia and Pavloff, Ulysse and Rapetti, Alexandre},
  title =	{{The Synchronization Power of Auditable Registers}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{4:1--4:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.4},
  URN =		{urn:nbn:de:0030-drops-194940},
  doi =		{10.4230/LIPIcs.OPODIS.2023.4},
  annote =	{Keywords: Auditability, atomic register, fault tolerance, consensus number}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.6
Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit

Authors: Hagit Attiya and Jennifer L. Welch

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
Algorithms to solve fault-tolerant consensus in asynchronous systems often rely on primitives such as crusader agreement, adopt-commit, and graded broadcast, which provide weaker agreement properties than consensus. Although these primitives have a similar flavor, they have been defined and implemented separately in ad hoc ways. We propose a new problem called connected consensus that has as special cases crusader agreement, adopt-commit, and graded broadcast, and generalizes them to handle multi-valued inputs. The generalization is accomplished by relating the problem to approximate agreement on graphs. We present three algorithms for multi-valued connected consensus in asynchronous message-passing systems, one tolerating crash failures and two tolerating malicious (unauthenticated Byzantine) failures. We extend the definition of binding, a desirable property recently identified as supporting binary consensus algorithms that are correct against adaptive adversaries, to the multi-valued input case and show that all our algorithms satisfy the property. Our crash-resilient algorithm has failure-resilience and time complexity that we show are optimal. When restricted to the case of binary inputs, the algorithm has improved time complexity over prior algorithms. Our two algorithms for malicious failures trade off failure resilience and time complexity. The first algorithm has time complexity that we prove is optimal but worse failure-resilience, while the second has failure-resilience that we prove is optimal but worse time complexity. When restricted to the case of binary inputs, the time complexity (as well as resilience) of the second algorithm matches that of prior algorithms. The contributions of the paper are first, a deeper insight into the connections between primitives commonly used to solve the fundamental problem of fault-tolerant consensus, and second, implementations of these primitives that can contribute to improved consensus algorithms.
Cite as

Hagit Attiya and Jennifer L. Welch. Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 6:1-6:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{attiya_et_al:LIPIcs.OPODIS.2023.6,
  author =	{Attiya, Hagit and Welch, Jennifer L.},
  title =	{{Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{6:1--6:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.6},
  URN =		{urn:nbn:de:0030-drops-194967},
  doi =		{10.4230/LIPIcs.OPODIS.2023.6},
  annote =	{Keywords: graded broadcast, gradecast, binding, approximate agreement}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.24
Recoverable and Detectable Self-Implementations of Swap

Authors: Tomer Lev Lehman, Hagit Attiya, and Danny Hendler

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
Recoverable algorithms tolerate failures and recoveries of processes by using non-volatile memory. Of particular interest are self-implementations of key operations, in which a recoverable operation is implemented from its non-recoverable counterpart (in addition to reads and writes). This paper presents two self-implementations of the swap operation. One works in the system-wide failures model, where all processes fail and recover together, and the other in the independent failures model, where each process crashes and recovers independently of the other processes. Both algorithms are wait-free in crash-free executions, but their recovery code is blocking. We prove that this is inherent for the independent failures model. The impossibility result is proved for implementations of distinguishable operations using interfering functions, and in particular, it applies to a recoverable self-implementation of swap.
Cite as

Tomer Lev Lehman, Hagit Attiya, and Danny Hendler. Recoverable and Detectable Self-Implementations of Swap. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 24:1-24:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{levlehman_et_al:LIPIcs.OPODIS.2023.24,
  author =	{Lev Lehman, Tomer and Attiya, Hagit and Hendler, Danny},
  title =	{{Recoverable and Detectable Self-Implementations of Swap}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{24:1--24:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.24},
  URN =		{urn:nbn:de:0030-drops-195140},
  doi =		{10.4230/LIPIcs.OPODIS.2023.24},
  annote =	{Keywords: Multi-core algorithms, persistent memory, non-volatile memory, recoverable objects, detectablitly}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2023.32
Bounds on Worst-Case Responsiveness for Agreement Algorithms

Authors: Hagit Attiya and Jennifer L. Welch

Published in: LIPIcs, Volume 286, 27th International Conference on Principles of Distributed Systems (OPODIS 2023)

Abstract
We study the worst-case time complexity of solving two agreement problems, consensus and broadcast, in systems with n processes subject to no more than t process failures. In both problems, correct processes must decide on a common value; in the consensus problem, each process has an input and if the inputs of correct processes are all the same, then that must be the common decision, whereas in the broadcast problem, only one process (the sender) has an input and if the sender is correct, then its input must be the common decision. We focus on systems where there is an upper bound Δ on the message delivery time but it is expected that typically, messages arrive much faster, say within some time d. While Δ may or may not be known in advance, d is inherently unknown and specific to each execution. The goal is to design deterministic algorithms whose running times have minimal to no dependence on Δ, a property called responsiveness. We present a generic algorithm transformation that, when applied to appropriate eventually-synchronous consensus (or broadcast) algorithms, results in consensus (or broadcast) algorithms for send omission failures, authenticated Byzantine failures, and unauthenticated Byzantine failures whose running times have no dependence on Δ; their worst-case time complexities are all O(td), which is asymptotically optimal. The algorithm for send omission failures requires n > 2t, while those for Byzantine failures, both authenticated and unauthenticated, require n > 3t. The failure-resilience of the unauthenticated Byzantine algorithm is optimal. For authenticated Byzantine failures, existing agreement algorithms provide worst-case time complexity O(t Δ) when n is at most 3t. (When n ≤ 2t, broadcast is solvable while consensus is not.) We prove a lower bound on the worst-case time complexity of ⌊(3t-n)/2⌋ d + Δ when n is at most 3t. Although lower bounds of Δ and (t+1)d were already known, our new lower bound indicates that, at least when n ≤ 2t, it is impossible for an algorithm to pay these bounds in parallel.
Cite as

Hagit Attiya and Jennifer L. Welch. Bounds on Worst-Case Responsiveness for Agreement Algorithms. In 27th International Conference on Principles of Distributed Systems (OPODIS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 286, pp. 32:1-32:22, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{attiya_et_al:LIPIcs.OPODIS.2023.32,
  author =	{Attiya, Hagit and Welch, Jennifer L.},
  title =	{{Bounds on Worst-Case Responsiveness for Agreement Algorithms}},
  booktitle =	{27th International Conference on Principles of Distributed Systems (OPODIS 2023)},
  pages =	{32:1--32:22},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-308-9},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{286},
  editor =	{Bessani, Alysson and D\'{e}fago, Xavier and Nakamura, Junya and Wada, Koichi and Yamauchi, Yukiko},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.OPODIS.2023.32},
  URN =		{urn:nbn:de:0030-drops-195229},
  doi =		{10.4230/LIPIcs.OPODIS.2023.32},
  annote =	{Keywords: bounded-delay model, basic round model, omission failures, Byzantine failures}
}
Document
DOI: 10.4230/LIPIcs.DISC.2023.4
One Step Forward, One Step Back: FLP-Style Proofs and the Round-Reduction Technique for Colorless Tasks

Authors: Hagit Attiya, Pierre Fraigniaud, Ami Paz, and Sergio Rajsbaum

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
The paper compares two generic techniques for deriving lower bounds and impossibility results in distributed computing. First, we prove a speedup theorem (a-la Brandt, 2019), for wait-free colorless algorithms, aiming at capturing the essence of the seminal round-reduction proof establishing a lower bound on the number of rounds for 3-coloring a cycle (Linial, 1992), and going by backward induction. Second, we consider FLP-style proofs, aiming at capturing the essence of the seminal consensus impossibility proof (Fischer, Lynch, and Paterson, 1985) and using forward induction. We show that despite their very different natures, these two forms of proof are tightly connected. In particular, we show that for every colorless task Π, if there is a round-reduction proof establishing the impossibility of solving Π using wait-free colorless algorithms, then there is an FLP-style proof establishing the same impossibility. For 1-dimensional colorless tasks (for an arbitrarily number n ≥ 2 of processes), we prove that the two proof techniques have exactly the same power, and more importantly, both are complete: if a 1-dimensional colorless task is not wait-free solvable by n ≥ 2 processes, then the impossibility can be proved by both proof techniques. Moreover, a round-reduction proof can be automatically derived, and an FLP-style proof can be automatically generated from it. Finally, we illustrate the use of these two techniques by establishing the impossibility of solving any colorless covering task of arbitrary dimension by wait-free algorithms.
Cite as

Hagit Attiya, Pierre Fraigniaud, Ami Paz, and Sergio Rajsbaum. One Step Forward, One Step Back: FLP-Style Proofs and the Round-Reduction Technique for Colorless Tasks. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 4:1-4:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{attiya_et_al:LIPIcs.DISC.2023.4,
  author =	{Attiya, Hagit and Fraigniaud, Pierre and Paz, Ami and Rajsbaum, Sergio},
  title =	{{One Step Forward, One Step Back: FLP-Style Proofs and the Round-Reduction Technique for Colorless Tasks}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{4:1--4:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.4},
  URN =		{urn:nbn:de:0030-drops-191304},
  doi =		{10.4230/LIPIcs.DISC.2023.4},
  annote =	{Keywords: Wait-free computing, lower bounds}
}
Document
DOI: 10.4230/LIPIcs.DISC.2023.5
Topological Characterization of Task Solvability in General Models of Computation

Authors: Hagit Attiya, Armando Castañeda, and Thomas Nowak

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
The famous asynchronous computability theorem (ACT) relates the existence of an asynchronous wait-free shared memory protocol for solving a task with the existence of a simplicial map from a subdivision of the simplicial complex representing the inputs to the simplicial complex representing the allowable outputs. The original theorem relies on a correspondence between protocols and simplicial maps in round-structured models of computation that induce a compact topology. This correspondence, however, is far from obvious for computation models that induce a non-compact topology, and indeed previous attempts to extend the ACT have failed. This paper shows that in every non-compact model, protocols solving tasks correspond to simplicial maps that need to be continuous. It first proves a generalized ACT for sub-IIS models, some of which are non-compact, and applies it to the set agreement task. Then it proves that in general models too, protocols are simplicial maps that need to be continuous, hence showing that the topological approach is universal. Finally, it shows that the approach used in ACT that equates protocols and simplicial complexes actually works for every compact model. Our study combines, for the first time, combinatorial and point-set topological aspects of the executions admitted by the computation model.
Cite as

Hagit Attiya, Armando Castañeda, and Thomas Nowak. Topological Characterization of Task Solvability in General Models of Computation. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 5:1-5:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{attiya_et_al:LIPIcs.DISC.2023.5,
  author =	{Attiya, Hagit and Casta\~{n}eda, Armando and Nowak, Thomas},
  title =	{{Topological Characterization of Task Solvability in General Models of Computation}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{5:1--5:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.5},
  URN =		{urn:nbn:de:0030-drops-191315},
  doi =		{10.4230/LIPIcs.DISC.2023.5},
  annote =	{Keywords: task solvability, combinatorial topology, point-set topology}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2023.36
Brief Announcement: Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit

Authors: Hagit Attiya and Jennifer L. Welch

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
Algorithms to solve fault-tolerant consensus in asynchronous systems often rely on primitives such as crusader agreement, adopt-commit, and graded broadcast, which provide weaker agreement properties than consensus. Although these primitives have a similar flavor, they have been defined and implemented separately in ad hoc ways. We propose a new problem called connected consensus that has as special cases crusader agreement, adopt-commit, and graded broadcast, and generalizes them to handle multi-valued (non-binary) inputs. The generalization is accomplished by relating the problem to approximate agreement on graphs. We present three algorithms for multi-valued connected consensus in asynchronous message-passing systems, one tolerating crash failures and two tolerating malicious (unauthenticated Byzantine) failures. We extend the definition of binding, a desirable property recently identified as supporting binary consensus algorithms that are correct against adaptive adversaries, to the multi-valued input case and show that all our algorithms satisfy the property. Our crash-resilient algorithm has failure-resilience and time complexity that we show are optimal. When restricted to the case of binary inputs, the algorithm has improved time complexity over prior algorithms. Our two algorithms for malicious failures trade off failure resilience and time complexity. The first algorithm has time complexity that we prove is optimal but worse failure-resilience, while the second has failure-resilience that we prove is optimal but worse time complexity. When restricted to the case of binary inputs, the time complexity (as well as resilience) of the second algorithm matches that of prior algorithms.
Cite as

Hagit Attiya and Jennifer L. Welch. Brief Announcement: Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 36:1-36:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{attiya_et_al:LIPIcs.DISC.2023.36,
  author =	{Attiya, Hagit and Welch, Jennifer L.},
  title =	{{Brief Announcement: Multi-Valued Connected Consensus: A New Perspective on Crusader Agreement and Adopt-Commit}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{36:1--36:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.36},
  URN =		{urn:nbn:de:0030-drops-191620},
  doi =		{10.4230/LIPIcs.DISC.2023.36},
  annote =	{Keywords: graded broadcast, gradecast, binding, approximate agreement}
}
Document
Brief Announcement
DOI: 10.4230/LIPIcs.DISC.2023.44
Brief Announcement: Recoverable and Detectable Self-Implementations of Swap

Authors: Tomer Lev Lehman, Hagit Attiya, and Danny Hendler

Published in: LIPIcs, Volume 281, 37th International Symposium on Distributed Computing (DISC 2023)

Abstract
Recoverable algorithms tolerate failures and recoveries of processes by using non-volatile memory. Of particular interest are self-implementations of key operations, in which a recoverable operation is implemented from its non-recoverable counterpart (in addition to reads and writes). This paper presents two self-implementations of the SWAP operation. One works in the system-wide failures model, where all processes fail and recover together, and the other in the independent failures model, where each process crashes and recovers independently of the other processes. Both algorithms are wait-free in crash-free executions, but their recovery code is blocking. We prove that this is inherent for the independent failures model. The impossibility result is proved for implementations of distinguishable operations using interfering functions, and in particular, it applies to a recoverable self-implementation of swap.
Cite as

Tomer Lev Lehman, Hagit Attiya, and Danny Hendler. Brief Announcement: Recoverable and Detectable Self-Implementations of Swap. In 37th International Symposium on Distributed Computing (DISC 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 281, pp. 44:1-44:7, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{levlehman_et_al:LIPIcs.DISC.2023.44,
  author =	{Lev Lehman, Tomer and Attiya, Hagit and Hendler, Danny},
  title =	{{Brief Announcement: Recoverable and Detectable Self-Implementations of Swap}},
  booktitle =	{37th International Symposium on Distributed Computing (DISC 2023)},
  pages =	{44:1--44:7},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-301-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{281},
  editor =	{Oshman, Rotem},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2023.44},
  URN =		{urn:nbn:de:0030-drops-191704},
  doi =		{10.4230/LIPIcs.DISC.2023.44},
  annote =	{Keywords: Persistent memory, non-volatile memory, recoverable objects, detectablitly}
}
Document
DOI: 10.4230/LIPIcs.CONCUR.2023.27
Faithful Simulation of Randomized BFT Protocols on Block DAGs

Authors: Hagit Attiya, Constantin Enea, and Shafik Nassar

Published in: LIPIcs, Volume 279, 34th International Conference on Concurrency Theory (CONCUR 2023)

Abstract
Byzantine Fault-Tolerant (BFT) protocols that are based on Directed Acyclic Graphs (DAGs) are attractive due to their many advantages in asynchronous blockchain systems. These DAG-based protocols can be viewed as a simulation of some BFT protocol on a DAG. Many DAG-based BFT protocols rely on randomization, since they are used for agreement and ordering of transactions, which cannot be achieved deterministically in asynchronous systems. Randomization is achieved either through local sources of randomness, or by employing shared objects that provide a common source of randomness, e.g., common coins. A DAG simulation of a randomized protocol should be faithful, in the sense that it precisely preserves the properties of the original BFT protocol, and in particular, their probability distributions. We argue that faithfulness is ensured by a forward simulation. We show how to faithfully simulate any BFT protocol that uses public coins and shared objects, like common coins.
Cite as

Hagit Attiya, Constantin Enea, and Shafik Nassar. Faithful Simulation of Randomized BFT Protocols on Block DAGs. In 34th International Conference on Concurrency Theory (CONCUR 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 279, pp. 27:1-27:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{attiya_et_al:LIPIcs.CONCUR.2023.27,
  author =	{Attiya, Hagit and Enea, Constantin and Nassar, Shafik},
  title =	{{Faithful Simulation of Randomized BFT Protocols on Block DAGs}},
  booktitle =	{34th International Conference on Concurrency Theory (CONCUR 2023)},
  pages =	{27:1--27:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-299-0},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{279},
  editor =	{P\'{e}rez, Guillermo A. and Raskin, Jean-Fran\c{c}ois},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2023.27},
  URN =		{urn:nbn:de:0030-drops-190210},
  doi =		{10.4230/LIPIcs.CONCUR.2023.27},
  annote =	{Keywords: Byzantine failures, Hyperproperties, Forward Simulation}
}
Document
DOI: 10.4230/DagRep.12.12.27
Formal Methods and Distributed Computing: Stronger Together (Dagstuhl Seminar 22492)

Authors: Hagit Attiya, Constantin Enea, Sergio Rajsbaum, and Ana Sokolova

Published in: Dagstuhl Reports, Volume 12, Issue 12 (2023)

Abstract
This report documents the program and the outcomes of Dagstuhl Seminar 22492 "Formal Methods and Distributed Computing: Stronger Together", held in December 2022.
Cite as

Hagit Attiya, Constantin Enea, Sergio Rajsbaum, and Ana Sokolova. Formal Methods and Distributed Computing: Stronger Together (Dagstuhl Seminar 22492). In Dagstuhl Reports, Volume 12, Issue 12, pp. 27-53, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@Article{attiya_et_al:DagRep.12.12.27,
  author =	{Attiya, Hagit and Enea, Constantin and Rajsbaum, Sergio and Sokolova, Ana},
  title =	{{Formal Methods and Distributed Computing: Stronger Together (Dagstuhl Seminar 22492)}},
  pages =	{27--53},
  journal =	{Dagstuhl Reports},
  ISSN =	{2192-5283},
  year =	{2023},
  volume =	{12},
  number =	{12},
  editor =	{Attiya, Hagit and Enea, Constantin and Rajsbaum, Sergio and Sokolova, Ana},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/DagRep.12.12.27},
  URN =		{urn:nbn:de:0030-drops-178452},
  doi =		{10.4230/DagRep.12.12.27},
  annote =	{Keywords: automated verification and reasoning, concurrent data structures and transactions, distributed algorithms, large-scale replication}
}
Document
DOI: 10.4230/LIPIcs.OPODIS.2022.6
The Step Complexity of Multidimensional Approximate Agreement

Authors: Hagit Attiya and Faith Ellen

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

Abstract
Approximate agreement allows a set of n processes to obtain outputs that are within a specified distance ε > 0 of one another and within the convex hull of the inputs. When the inputs are real numbers, there is a wait-free shared-memory approximate agreement algorithm [Moran, 1995] whose step complexity is in O(n log(S/ε)), where S, the spread of the inputs, is the maximal distance between inputs. There is another wait-free algorithm [Schenk, 1995] that avoids the dependence on n and achieves O(log(M/ε)) step complexity where M, the magnitude of the inputs, is the absolute value of the maximal input. This paper considers whether it is possible to obtain an approximate agreement algorithm whose step complexity depends on neither n nor the magnitude of the inputs, which can be much larger than their spread. On the negative side, we prove that Ω(min{(log M)/(log log M), (√log n)/(log log n)}) is a lower bound on the step complexity of approximate agreement, even when the inputs are real numbers. On the positive side, we prove that a polylogarithmic dependence on n and S/ε can be achieved, by presenting an approximate agreement algorithm with O(log n (log n + log(S/ε))) step complexity. Our algorithm works for multidimensional domains. The step complexity can be further restricted to be in O(min{log n (log n + log (S/ε)), log(M/ε)}) when the inputs are real numbers.
Cite as

Hagit Attiya and Faith Ellen. The Step Complexity of Multidimensional Approximate Agreement. In 26th International Conference on Principles of Distributed Systems (OPODIS 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 253, pp. 6:1-6:12, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{attiya_et_al:LIPIcs.OPODIS.2022.6,
  author =	{Attiya, Hagit and Ellen, Faith},
  title =	{{The Step Complexity of Multidimensional Approximate Agreement}},
  booktitle =	{26th International Conference on Principles of Distributed Systems (OPODIS 2022)},
  pages =	{6:1--6:12},
  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.2022.6},
  URN =		{urn:nbn:de:0030-drops-176261},
  doi =		{10.4230/LIPIcs.OPODIS.2022.6},
  annote =	{Keywords: approximate agreement, conflict detection, shared memory, wait-freedom, step complexity}
}
Document
Invited Talk
DOI: 10.4230/LIPIcs.DISC.2022.3
Using Linearizable Objects in Randomized Concurrent Programs (Invited Talk)

Authors: Jennifer L. Welch

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
Atomic shared objects, whose operations take place instantaneously, are a powerful technique for designing complex concurrent programs. Since they are not always available, they are typically substituted with software implementations. A prominent condition relating these implementations to their atomic specifications is linearizability, which preserves safety properties of programs using them. However linearizability does not preserve hyper-properties, which include probabilistic guarantees about randomized programs. A more restrictive property, strong linearizability, does preserve hyper-properties but it is impossible to achieve in many situations. In particular, we show that there are no strongly linearizable implementations of multi-writer registers or snapshot objects in message-passing systems. On the other hand, we show that a wide class of linearizable implementations, including well-known ones for registers and snapshots, can be modified to approximate the probabilistic guarantees of randomized programs when using atomic objects. This is joint work with Hagit Attiya and Constantin Enea.
Cite as

Jennifer L. Welch. Using Linearizable Objects in Randomized Concurrent Programs (Invited Talk). In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, p. 3:1, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{welch:LIPIcs.DISC.2022.3,
  author =	{Welch, Jennifer L.},
  title =	{{Using Linearizable Objects in Randomized Concurrent Programs}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{3:1--3:1},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.3},
  URN =		{urn:nbn:de:0030-drops-171946},
  doi =		{10.4230/LIPIcs.DISC.2022.3},
  annote =	{Keywords: Concurrent objects, strong linearizability, impossibility proofs, message-passing systems, randomized algorithms}
}
Document
DOI: 10.4230/LIPIcs.DISC.2022.12
Liveness and Latency of Byzantine State-Machine Replication

Authors: Manuel Bravo, Gregory Chockler, and Alexey Gotsman

Published in: LIPIcs, Volume 246, 36th International Symposium on Distributed Computing (DISC 2022)

Abstract
Byzantine state-machine replication (SMR) ensures the consistency of replicated state in the presence of malicious replicas and lies at the heart of the modern blockchain technology. Byzantine SMR protocols often guarantee safety under all circumstances and liveness only under synchrony. However, guaranteeing liveness even under this assumption is nontrivial. So far we have lacked systematic ways of incorporating liveness mechanisms into Byzantine SMR protocols, which often led to subtle bugs. To close this gap, we introduce a modular framework to facilitate the design of provably live and efficient Byzantine SMR protocols. Our framework relies on a view abstraction generated by a special SMR synchronizer primitive to drive the agreement on command ordering. We present a simple formal specification of an SMR synchronizer and its bounded-space implementation under partial synchrony. We also apply our specification to prove liveness and analyze the latency of three Byzantine SMR protocols via a uniform methodology. In particular, one of these results yields what we believe is the first rigorous liveness proof for the algorithmic core of the seminal PBFT protocol.
Cite as

Manuel Bravo, Gregory Chockler, and Alexey Gotsman. Liveness and Latency of Byzantine State-Machine Replication. In 36th International Symposium on Distributed Computing (DISC 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 246, pp. 12:1-12:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bravo_et_al:LIPIcs.DISC.2022.12,
  author =	{Bravo, Manuel and Chockler, Gregory and Gotsman, Alexey},
  title =	{{Liveness and Latency of Byzantine State-Machine Replication}},
  booktitle =	{36th International Symposium on Distributed Computing (DISC 2022)},
  pages =	{12:1--12:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-255-6},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{246},
  editor =	{Scheideler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.DISC.2022.12},
  URN =		{urn:nbn:de:0030-drops-172037},
  doi =		{10.4230/LIPIcs.DISC.2022.12},
  annote =	{Keywords: Replication, blockchain, partial synchrony, liveness}
}
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