Submission date: 2020-09-30
 Publication date: 2021-07-15
 DOI: https://doi.org/10.22152/programming-journal.org/2022/6/3
 Full text: PDF A future

An Optimised Flow for Futures: From Theory to Practice

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2023-03-15 12:00:05

Submission date: 2020-09-30 Publication date: 2021-07-15 DOI: https://doi.org/10.22152/programming-journal.org/2022/6/3 Full text: PDF

A future is an entity representing the result of an ongoing computation. A synchronisation with a “get” operation blocks the caller until the computation is over, to return the corresponding value. When a computation in charge of fulfilling a future delegates part of its processing to another task, mainstream languages return nested futures, and several “get” operations are needed to retrieve the computed value (we call such futures “control-flow futures”). Several approaches were proposed to tackle this issues: the “forward” construct, that allows the programmer to make delegation explicit and avoid nested futures, and “data-flow explicit futures” which natively collapse nested futures into plain futures.

This paper supports the claim that data-flow explicit futures form a powerful set of language primitives, on top of which other approaches can be built. We prove the equivalence, in the context of data-flow explicit futures, between the “forward” construct and classical “return” from functions. The proof relies on a branching bisimulation between a program using “forward” and its “return” counterpart. This result allows language designers to consider “forward” as an optimisation directive rather than as a language primitive.

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