|
In computer science, future, promise, and delay refer to constructs used for synchronization in some concurrent programming languages. They describe an object that acts as a proxy for a result that is initially unknown, usually because the computation of its value is yet incomplete. The term ''promise'' was proposed in 1976 by Daniel P. Friedman and David Wise, and Peter Hibbard called it ''eventual''. A somewhat similar concept ''future'' was introduced in 1977 in a paper by Henry Baker and Carl Hewitt.〔 〕 The terms ''future'', ''promise'', and ''delay'' are often used interchangeably, although some differences in usage between ''future'' and ''promise'' are treated below. Specifically, when usage is distinguished, a future is a ''read-only'' placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the future.〔"(SIP-14 - Futures and Promises )"〕 Notably, a future may be defined without specifying which specific promise will set its value, and different possible promises may set the value of a given future, though this can be done only once for a given future. In other cases a future and a promise are created together and associated with each other: the future is the value, the promise is the function that sets the value – essentially the return value (future) of an asynchronous function (promise). Setting the value of a future is also called ''resolving'', ''fulfilling'', or ''binding'' it. ==Applications== Futures and promises originated in functional programming and related paradigms (such as logic programming) to decouple a value (a future) from how it was computed (a promise), allowing the computation to be done more flexibly, notably by parallelizing it. It later found use in distributed computing, in reducing the latency from communication round trips. More recently, it has gained popularity by allowing writing asynchronous programs in direct style, rather than in continuation-passing style. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「futures and promises」の詳細全文を読む スポンサード リンク
|