Seq no more: better strategies for parallel Haskell

Marlow, S., Maier, P., Loidl, H.-W., Aswad, M.K. and Trinder, P. (2010) Seq no more: better strategies for parallel Haskell. In: Proceedings of the Third ACM Haskell Symposium on Haskell, Baltimore, MD, USA, 30 Sept 2010. ACM: New York, NY, USA, pp. 91-102. ISBN 9781450302524

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Abstract

We present a complete redesign of evaluation strategies, a key abstraction for specifying pure, deterministic parallelism in Haskell. Our new formulation preserves the compositionality and modularity benefits of the original, while providing significant new benefits. First, we introduce an evaluation-order monad to provide clearer, more generic, and more efficient specification of parallel evaluation. Secondly, the new formulation resolves a subtle space management issue with the original strategies, allowing parallelism (sparks) to be preserved while reclaiming heap associated with superfluous parallelism. Related to this, the new formulation provides far better support for speculative parallelism as the garbage collector now prunes unneeded speculation. Finally, the new formulation provides improved compositionality: we can directly express parallelism embedded within lazy data structures, producing more compositional strategies, and our basic strategies are parametric in the coordination combinator, facilitating a richer set of parallelism combinators.

We give measurements over a range of benchmarks demonstrating that the runtime overheads of the new formulation relative to the original are low, and the new strategies even yield slightly better speedups on average than the original strategies.

Item Type:Book Sections
Status:Published
Glasgow Author(s) Enlighten ID:Trinder, Professor Phil
Authors: Marlow, S., Maier, P., Loidl, H.-W., Aswad, M.K., and Trinder, P.
College/School:College of Science and Engineering > School of Computing Science
Publisher:ACM
ISBN:9781450302524

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