Obstruction-Free Algorithms Can Be Practically Wait-Free

Fich, Faith E.; Luchangco, Victor; Moir, Mark; Shavit, Nir

doi:10.1007/11561927_8

Cited by 46 publications

(53 citation statements)

References 21 publications

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“…The relation between waitfreedom and obstruction-freedom has been investigated before: Fich, Luchangco, Moir, and Shavit [19] showed that obstruction-free algorithms can be transformed to wait-free ones in the unknown-bound semi-synchronous model.…”

Section: Theoremmentioning

confidence: 99%

An $O(\sqrt n)$ Space Bound for Obstruction-Free Leader Election

Giakkoupis

Helmi

Highám

et al. 2013

Lecture Notes in Computer Science

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Abstract. We present a deterministic obstruction-free implementation of leader election from O( √ n) atomic O(log n)-bit registers in the standard asynchronous shared memory system with n processes. We provide also a technique to transform any deterministic obstruction-free algorithm, in which any process can finish if it runs for b steps without interference, into a randomized wait-free algorithm for the oblivious adversary, in which the expected step complexity is polynomial in n and b. This transformation allows us to combine our obstruction-free algorithm with the leader election algorithm by Giakkoupis and Woelfel [21], to obtain a fast randomized leader election (and thus test-and-set) implementation from O( √ n) O(log n)-bit registers, that has expected step complexity O(log * n) against the oblivious adversary. Our algorithm provides the first sub-linear space upper bound for obstruction-free leader election. A lower bound of Ω(log n) has been known since 1989 [29]. Our research is also motivated by the long-standing open problem whether there is an obstruction-free consensus algorithm which uses fewer than n registers.

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Section: Theoremmentioning

confidence: 99%

An $O(\sqrt n)$ Space Bound for Obstruction-Free Leader Election

Giakkoupis

Helmi

Highám

et al. 2013

Lecture Notes in Computer Science

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“…Our contention manager implementations share many similarities with the algorithms of [10] and [14], both of which ensure wait-freedom, but use timeout-based failure detection mechanisms directly. In fact, the techniques used in all these algorithms originate in indulgent algorithms [13] designed for partially synchronous systems [7,8,24], ported later to shared memory systems [5,12].…”

Section: Related Workmentioning

confidence: 99%

The weakest failure detectors to boost obstruction-freedom

2007

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It is considered good practice in concurrent computing to devise shared object implementations that ensure a minimal obstruction-free progress property and delegate the task of boosting liveness to independent generic oracles called contention managers. This paper determines necessary and sufficient conditions to implement wait-free and non-blocking contention managers, i.e., contention managers that ensure wait-freedom (resp. non-blockingness) of any associated obstruction-free object implementation. The necessary conditions hold even when universal objects (like compare-and-swap) or random oracles are available in the implementation of the contention manager. On the other hand, the sufficient conditions assume only basic read/write objects, i.e., registers. We show that failure detector ♦P is the weakest to convert any obstruction-free algorithm into a wait-free one, and Ω * , a new failure detector which we introduce in this paper, and which is strictly weaker than ♦P but strictly stronger than Ω, is the weakest to convert any obstruction-free algorithm into a non-blocking one. We also address the issue of minimizing the overhead imposed by contention management in low contention scenarios. We propose two intermittent failure detectors I Ω * and I ♦P that are in a precise sense equivalent to, respectively, Ω * and ♦P, but allow for reducing the cost of failure detection in eventually synchronous systems when there is little contention. We present two contention managers: a non-blocking one and a wait-free one, that use, respectively, I Ω * and I ♦P . When there is no contention, the first induces very little overhead whereas the second induces some non-trivial overhead. We show that wait-free contention managers, unlike their nonblocking counterparts, impose an inherent non-trivial overhead even in contention-free executions.

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“…Our work is based on the transformation presented in [5]. A comprehensive discussion of wait-free synchronization is given in [8].…”

Section: Related Workmentioning

confidence: 99%

“…Obstruction-freedom is weaker than non-blocking which, in turn, is weaker than wait-freedom. While obstruction-freedom and non-blocking have the potential to significantly improve the performance of concurrent applications, wait-freedom (although desirable) imposes too much overhead upon the implementation.In [5], Fich, Luchangco, Moir, and Shavit have presented an interesting transformation that converts any obstruction-free algorithm into a waitfree algorithm when analyzed in the unknown-bound semi-synchronous model. The FLMS transformation uses n atomic single-writer registers, n atomic multi-writer registers and a single fetch-and-increment object, where n is the number of processes.…”

mentioning

confidence: 99%

“…In [5], Fich, Luchangco, Moir, and Shavit have presented an interesting transformation that converts any obstruction-free algorithm into a waitfree algorithm when analyzed in the unknown-bound semi-synchronous model. The FLMS transformation uses n atomic single-writer registers, n atomic multi-writer registers and a single fetch-and-increment object, where n is the number of processes.…”

mentioning

confidence: 99%

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Efficient Transformations of Obstruction-Free Algorithms into Non-blocking Algorithms

Taubenfeld

Lecture Notes in Computer Science

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Abstract. Three well studied progress conditions for implementing concurrent algorithms without locking are, obstruction-freedom, non-blocking and wait-freedom. Obstruction-freedom is weaker than non-blocking which, in turn, is weaker than wait-freedom. While obstruction-freedom and non-blocking have the potential to significantly improve the performance of concurrent applications, wait-freedom (although desirable) imposes too much overhead upon the implementation.In [5], Fich, Luchangco, Moir, and Shavit have presented an interesting transformation that converts any obstruction-free algorithm into a waitfree algorithm when analyzed in the unknown-bound semi-synchronous model. The FLMS transformation uses n atomic single-writer registers, n atomic multi-writer registers and a single fetch-and-increment object, where n is the number of processes.We define a time complexity measure for analyzing such transformations, and prove that the time complexity of the FLMS transformation is exponential in the number of processes n. This leads naturally to the question of whether the time and/or space complexity of the FLMS transformation can be improved by relaxing the wait-freedom progress condition. We present several efficient transformations that convert any obstruction-free algorithm into a non-blocking algorithm when analyzed in the unknown-bound semi-synchronous model. All our transformations have O(1) time complexity. One transformation uses n atomic singlewriter registers and a single compare-and-swap object; another transformation uses only a single compare-and-swap object which is assumed to support also a read operation.

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Obstruction-Free Algorithms Can Be Practically Wait-Free

Cited by 46 publications

References 21 publications

An $O(\sqrt n)$ Space Bound for Obstruction-Free Leader Election

An $O(\sqrt n)$ Space Bound for Obstruction-Free Leader Election

The weakest failure detectors to boost obstruction-freedom

Efficient Transformations of Obstruction-Free Algorithms into Non-blocking Algorithms

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