Quicksort: Combining Concurrency, Recursion, and Mutable Data Structures

  • David Kitchin
  • Adrian Quark
  • Jayadev Misra


Quicksort (Commun. ACM 4(7):321–322, 1961) remains one of the most studied algorithms in computer science. It is important not only as a practical sorting method, but also as a splendid teaching aid for introducing recursion and systematic algorithm development. The algorithm has been studied extensively; so, it is natural to assume that everything that needs to be said about it has already been said. Yet, in attempting to code it using a recent programming language of our design, we discovered that its structure is more clearly expressed as a concurrent program that manipulates a shared mutable store, without any locking or explicit synchronization. In this paper, we describe the essential aspects of our programming language Orc (Proceedings of FMOODS/FORTE, vol. 5522 of LNCS, pp. 1–25. Springer 2009), show a number of examples that combine its features in various forms, and then develop a concise description of Quicksort. We hope to highlight the importance of including concurrency, recursion and mutability within a single theory.


Concurrent Programming Site Call Syntactic Sugar FIFO Channel Site Library 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



Jayadev Misra is deeply grateful to Tony Hoare for research ideas, inspiration,and personal friendship spanning over 3 decades. It is no exaggeration that hewould not have pursued certain research directions, that have ultimately provedquite successful, had it not been for Tony’s encouragement. This paper is a smalltoken of appreciation.

The authors are indebted to Doug McIlroy and Manuel Serrano fortheir careful reading of this manuscript and many perceptive commentsand suggestions. Our long-time collaborators, Albert Benveniste, ClaudeJard, and Jose Meseguer have helped us refine the underlying ideas ofOrc.

This work is partially supported by National Science Foundation grant CCF-0811536.


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Copyright information

© Springer London 2010

Authors and Affiliations

  1. 1.University of Texas at AustinAustinUSA

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