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DOI: 10.4230/LIPIcs.ECOOP.2017.6

Relaxed Linear References for Lock-free Data Structures

Authors: Elias Castegren and Tobias Wrigstad

Published in: LIPIcs, Volume 74, 31st European Conference on Object-Oriented Programming (ECOOP 2017)

Abstract

Linear references are guaranteed to be free from aliases. This is a strong property that simplifies reasoning about programs and enables powerful optimisations, but it is also a property that is too strong for many applications. Notably, lock-free algorithms, which implement protocols that ensure safe, non-blocking concurrent access to data structures, are generally not typable with linear references because they rely on aliasing to achieve lock-freedom. This paper presents LOLCAT, a type system with a relaxed notion of linearity that allows an unbounded number of aliases to an object as long as at most one alias at a time owns the right to access the contents of the object. This ownership can be transferred between aliases, but can never be duplicated. types are powerful enough to type several lock-free data structures and give a compile-time guarantee of absence of data-races when accessing owned data. In particular, LOLCAT is able to assign types to the CAS (compare and swap) primitive that precisely describe how ownership is transferred across aliases, possibly across different threads. The paper introduces LOLCAT through a sound core procedural calculus, and shows how LOLCAT can be applied to three fundamental lock-free data structures. It also discusses a prototype implementation which integrates LOLCAT with an object-oriented programming language.

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Elias Castegren and Tobias Wrigstad. Relaxed Linear References for Lock-free Data Structures. In 31st European Conference on Object-Oriented Programming (ECOOP 2017). Leibniz International Proceedings in Informatics (LIPIcs), Volume 74, pp. 6:1-6:32, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2017)

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@InProceedings{castegren_et_al:LIPIcs.ECOOP.2017.6,
  author =	{Castegren, Elias and Wrigstad, Tobias},
  title =	{{Relaxed Linear References for Lock-free Data Structures}},
  booktitle =	{31st European Conference on Object-Oriented Programming (ECOOP 2017)},
  pages =	{6:1--6:32},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-035-4},
  ISSN =	{1868-8969},
  year =	{2017},
  volume =	{74},
  editor =	{M\"{u}ller, Peter},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2017.6},
  URN =		{urn:nbn:de:0030-drops-72670},
  doi =		{10.4230/LIPIcs.ECOOP.2017.6},
  annote =	{Keywords: Type systems, Concurrency, Lock-free programming}
}

Document

DOI: 10.4230/LIPIcs.ECOOP.2016.5

Reference Capabilities for Concurrency Control

Authors: Elias Castegren and Tobias Wrigstad

Published in: LIPIcs, Volume 56, 30th European Conference on Object-Oriented Programming (ECOOP 2016)

Abstract

The proliferation of shared mutable state in object-oriented programming complicates software development as two seemingly unrelated operations may interact via an alias and produce unexpected results. In concurrent programming this manifests itself as data-races. Concurrent object-oriented programming further suffers from the fact that code that warrants synchronisation cannot easily be distinguished from code that does not. The burden is placed solely on the programmer to reason about alias freedom, sharing across threads and side-effects to deduce where and when to apply concurrency control, without inadvertently blocking parallelism. This paper presents a reference capability approach to concurrent and parallel object-oriented programming where all uses of aliases are guaranteed to be data-race free. The static type of an alias describes its possible sharing without using explicit ownership or effect annotations. Type information can express non-interfering deterministic parallelism without dynamic concurrency control, thread-locality, lock-based schemes, and guarded-by relations giving multi-object atomicity to nested data structures. Unification of capabilities and traits allows trait-based reuse across multiple concurrency scenarios with minimal code duplication. The resulting system brings together features from a wide range of prior work in a unified way.

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Elias Castegren and Tobias Wrigstad. Reference Capabilities for Concurrency Control. In 30th European Conference on Object-Oriented Programming (ECOOP 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 56, pp. 5:1-5:26, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{castegren_et_al:LIPIcs.ECOOP.2016.5,
  author =	{Castegren, Elias and Wrigstad, Tobias},
  title =	{{Reference Capabilities for Concurrency Control}},
  booktitle =	{30th European Conference on Object-Oriented Programming (ECOOP 2016)},
  pages =	{5:1--5:26},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-014-9},
  ISSN =	{1868-8969},
  year =	{2016},
  volume =	{56},
  editor =	{Krishnamurthi, Shriram and Lerner, Benjamin S.},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECOOP.2016.5},
  URN =		{urn:nbn:de:0030-drops-60998},
  doi =		{10.4230/LIPIcs.ECOOP.2016.5},
  annote =	{Keywords: Type systems, Capabilities, Traits, Concurrency, Object-Oriented}
}

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Relaxed Linear References for Lock-free Data Structures

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Reference Capabilities for Concurrency Control

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