如何限制 Q promise 并发? [英] How can I limit Q promise concurrency?

问题描述

如何编写限制Q promise并发的方法?

How do I write a method that limits Q promise concurrency?

例如，我有一个方法 spawnProcess.它返回一个 Q 承诺.
我希望一次生成的进程不超过 5 个，但对调用代码透明.

For instance, I have a method spawnProcess. It returns a Q promise.
I want no more than 5 process spawned at a time, but transparently to the calling code.

我需要实现的是一个带签名的函数

What I need to implement is a function with signature

function limitConcurrency(promiseFactory, limit)

我可以这样称呼

spawnProcess = limitConcurrency(spawnProcess, 5);

// use spawnProcess as usual

我已经开始研究我的版本，但我想知道是否有人有我可以检查的简洁实现.

I already started working on my version, but I wonder if anyone has a concise implementation that I can check against.

推荐答案

我有一个库可以为您执行此操作 https://github.com/ForbesLindesay/throat

I have a library that does this for you https://github.com/ForbesLindesay/throat

您可以通过 browserify 使用它或从 brcdn (https://www.brcdn.org/?module=throat&version=latest) 并将其添加为脚本标记.

You can use it via browserify or download the standalone build from brcdn (https://www.brcdn.org/?module=throat&version=latest) and add it as a script tag.

然后(假设 Promise 构造函数是 polyfill 或在您的环境中实现)您可以执行以下操作:

Then (assuming the Promise constructor is polyfilled or implemented in your environment) you can do:

//remove this line if using standalone build
var throat = require('throat');

function limitConcurrency(promiseFactory, limit) {
  var fn = throat(promiseFactory, limit);
  return function () {
    return Q(fn.apply(this, arguments));
  }
}

你可以直接调用 throat(promiseFactory, limit) 但这会返回一个 promise 承诺而不是 Q 承诺.

You could just call throat(promiseFactory, limit) directly but that would return a promise promise rather than a Q promise.

我也非常喜欢将它与 array.map 一起使用.

I also really like using it with array.map.

// only allow 3 parallel downloads
var downloadedItems = Q.all(items.map(throat(download, 3)));

这篇关于如何限制 Q promise 并发?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！