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Documents authored by Chini, Peter

Document
DOI: 10.4230/LIPIcs.FSTTCS.2020.42
A Framework for Consistency Algorithms

Authors: Peter Chini and Prakash Saivasan

Published in: LIPIcs, Volume 182, 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)

Abstract
We present a framework that provides deterministic consistency algorithms for given memory models. Such an algorithm checks whether the executions of a shared-memory concurrent program are consistent under the axioms defined by a model. For memory models like SC and TSO, checking consistency is NP-complete. Our framework shows, that despite the hardness, fast deterministic consistency algorithms can be obtained by employing tools from fine-grained complexity. The framework is based on a universal consistency problem which can be instantiated by different memory models. We construct an algorithm for the problem running in time 𝒪^*(2^k), where k is the number of write accesses in the execution that is checked for consistency. Each instance of the framework then admits an 𝒪^*(2^k)-time consistency algorithm. By applying the framework, we obtain corresponding consistency algorithms for SC, TSO, PSO, and RMO. Moreover, we show that the obtained algorithms for SC, TSO, and PSO are optimal in the fine-grained sense: there is no consistency algorithm for these running in time 2^{o(k)} unless the exponential time hypothesis fails.
Cite as

Peter Chini and Prakash Saivasan. A Framework for Consistency Algorithms. In 40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 182, pp. 42:1-42:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{chini_et_al:LIPIcs.FSTTCS.2020.42,
  author =	{Chini, Peter and Saivasan, Prakash},
  title =	{{A Framework for Consistency Algorithms}},
  booktitle =	{40th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2020)},
  pages =	{42:1--42:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-174-0},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{182},
  editor =	{Saxena, Nitin and Simon, Sunil},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2020.42},
  URN =		{urn:nbn:de:0030-drops-132833},
  doi =		{10.4230/LIPIcs.FSTTCS.2020.42},
  annote =	{Keywords: Consistency, Weak Memory, Fine-Grained Complexity}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2019.37
Complexity of Liveness in Parameterized Systems

Authors: Peter Chini, Roland Meyer, and Prakash Saivasan

Published in: LIPIcs, Volume 150, 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)

Abstract
We investigate the fine-grained complexity of liveness verification for leader contributor systems. These consist of a designated leader thread and an arbitrary number of identical contributor threads communicating via a shared memory. The liveness verification problem asks whether there is an infinite computation of the system in which the leader reaches a final state infinitely often. Like its reachability counterpart, the problem is known to be NP-complete. Our results show that, even from a fine-grained point of view, the complexities differ only by a polynomial factor. Liveness verification decomposes into reachability and cycle detection. We present a fixed point iteration solving the latter in polynomial time. For reachability, we reconsider the two standard parameterizations. When parameterized by the number of states of the leader L and the size of the data domain D, we show an (L + D)^O(L + D)-time algorithm. It improves on a previous algorithm, thereby settling an open problem. When parameterized by the number of states of the contributor C, we reuse an O^*(2^C)-time algorithm. We show how to connect both algorithms with the cycle detection to obtain algorithms for liveness verification. The running times of the composed algorithms match those of reachability, proving that the fine-grained lower bounds for liveness verification are met.
Cite as

Peter Chini, Roland Meyer, and Prakash Saivasan. Complexity of Liveness in Parameterized Systems. In 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 150, pp. 37:1-37:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{chini_et_al:LIPIcs.FSTTCS.2019.37,
  author =	{Chini, Peter and Meyer, Roland and Saivasan, Prakash},
  title =	{{Complexity of Liveness in Parameterized Systems}},
  booktitle =	{39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)},
  pages =	{37:1--37:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-131-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{150},
  editor =	{Chattopadhyay, Arkadev and Gastin, Paul},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2019.37},
  URN =		{urn:nbn:de:0030-drops-115993},
  doi =		{10.4230/LIPIcs.FSTTCS.2019.37},
  annote =	{Keywords: Liveness Verification, Fine-Grained Complexity, Parameterized Systems}
}
Document
DOI: 10.4230/LIPIcs.ESA.2017.27
On the Complexity of Bounded Context Switching

Authors: Peter Chini, Jonathan Kolberg, Andreas Krebs, Roland Meyer, and Prakash Saivasan

Published in: LIPIcs, Volume 87, 25th Annual European Symposium on Algorithms (ESA 2017)

Abstract
Bounded context switching (BCS) is an under-approximate method for finding violations to safety properties in shared-memory concurrent programs. Technically, BCS is a reachability problem that is known to be NP-complete. Our contribution is a parameterized analysis of BCS. The first result is an algorithm that solves BCS when parameterized by the number of context switches (cs) and the size of the memory (m) in O*(m^(cs)2^(cs)). This is achieved by creating instances of the easier problem Shuff which we solve via fast subset convolution. We also present a lower bound for BCS of the form m^o(cs / log(cs)), based on the exponential time hypothesis. Interestingly, the gap is closely related to a conjecture that has been open since FOCS'07. Further, we prove that BCS admits no polynomial kernel. Next, we introduce a measure, called scheduling dimension, that captures the complexity of schedules. We study BCS parameterized by the scheduling dimension (sdim) and show that it can be solved in O*((2m)^(4sdim)4^t), where t is the number of threads. We consider variants of the problem for which we obtain (matching) upper and lower bounds.
Cite as

Peter Chini, Jonathan Kolberg, Andreas Krebs, Roland Meyer, and Prakash Saivasan. On the Complexity of Bounded Context Switching. In 25th Annual European Symposium on Algorithms (ESA 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 87, pp. 27:1-27:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{chini_et_al:LIPIcs.ESA.2017.27,
  author =	{Chini, Peter and Kolberg, Jonathan and Krebs, Andreas and Meyer, Roland and Saivasan, Prakash},
  title =	{{On the Complexity of Bounded Context Switching}},
  booktitle =	{25th Annual European Symposium on Algorithms (ESA 2017)},
  pages =	{27:1--27:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-049-1},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{87},
  editor =	{Pruhs, Kirk and Sohler, Christian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ESA.2017.27},
  URN =		{urn:nbn:de:0030-drops-78730},
  doi =		{10.4230/LIPIcs.ESA.2017.27},
  annote =	{Keywords: Shared memory concurrency, safety verification, fixed-parameter tractability, exponential time hypothesis, bounded context switching}
}
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