samskivert: A Type and Effect System for Deterministic Parallel Java – Bocchino, et al.

06 March 2010

Summary
Describes a language, Deterministic Parallel Java, which extends Java with parallel constructs (cobegin and foreach) and a type and effect system that guarantees deterministic semantics for said constructs. Describes region-based type and effect system including: named regions, region parameters, disjointness constraints, method effect summaries (for modular checking), region path lists (for describing nested regions), partially specified regions (for describing recursive algorithms), index-parametrized arrays, and sub-arrays. Manual commutativity annotations can be added to communicate invariants inexpressible in the type system.

Comments
Providing light-weight parallelized primitives is clearly an important step toward more wide-spread use of parallelism in every day programs. If you have problems amenable to parallel divide-and-conquer solutions, then cobegin and foreach are going to be your friends, and index-parametrized arrays and sub-arrays will allow you to express your algorithm in a way that DPJ can prove has no data races.

When things get messier and you have a mishmash of computations where some are parallelizable and some are just concurrently executable (maybe they block on disk or network I/O) and you want to weave these all together with a type system to point out any “sharing accidents”, I’m not sure how useful something like DPJ is going to be. That’s not to say that there’s obviously a better approach that does reconcile a more ad hoc workload, and maybe DPJ is a step toward such a thing. It may be that something like Kilim is a more appropriate abstraction for general-purpose computing. Or perhaps these approaches are orthogonal.

Source: PDF ACM

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