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

问题描述

我如何写一个限制Q promise并发的方法？

例如，我有一个方法 spawnProcess 。它返回一个Q promise。

我一次只能生成5个进程，但透明的调用代码。

我需要什么实现是一个带有签名的函数

 函数limitConcurrency（promiseFactory，limit）
  / pre> 
 
 
我可以调用像
  spawnProcess = limitConcurrency spawnProcess，5）; 
 
 //照常使用spawnProcess 
  
我已经开始使用我的版本，但我不知道有没有一个简洁的实现，我可以检查。
解决方案
我有一个库 https://github.com/ForbesLindesay/throat  
 
 
 
您可以通过browserify使用它，也可以从brcdn下载独立版本（ https：/ /www.brcdn.org/?module=throat&version=latest ）并将其添加为脚本标记。
 
 
 
然后（假设 Promise 构造函数在你的环境中是polyfilled或实现的）你可以这样做：
 如果使用独立构建，请删除此行
 var throat = require（'throat'）; 
 
 function limitConcurrency（promiseFactory，limit）{
 var fn = throat（promiseFactory，limit）; 
 return function（）{
 return Q（fn.apply（this，arguments））; 
} 
} 
  
您可以调用 throat （promiseFactory，limit），但会返回 promise  promise，而不是Q promise。
 
 
 
我也非常喜欢使用array.map。
  //只允许3个并行下载
 var downloadedItems = Q.all（items.map（throat（download，3）））; 
  
 
How do I write a method that limits Q promise concurrency?

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.

What I need to implement is a function with signature
function limitConcurrency(promiseFactory, limit)
that I can call like
spawnProcess = limitConcurrency(spawnProcess, 5);

// use spawnProcess as usual
I already started working on my version, but I wonder if anyone has a concise implementation that I can check against.
解决方案
I have a library that does this for you https://github.com/ForbesLindesay/throat

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.

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

I also really like using it with array.map.
// only allow 3 parallel downloads
var downloadedItems = Q.all(items.map(throat(download, 3)));


                        
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