限制Node.js的异步调用

问题描述

我有一个Node.js的应用程序，在本地获取文件列表并上传到服务器。这个列表可以包含成千上万的文件。

I've got a Node.js app that gets a list of file locally and uploads them to a server. This list could contain thousands of files.

for (var i = 0; i < files.length; i++) {
   upload_file(files[i]);
}

如果我与成千上万的文件执行此，upload_file将调用数千次全部一次，而最有可能的模具（或至少斗争）。在同步的世界里，我们会创建一个线程池，它限制在一定的数量的线程。有一个简单的办法来限制多少异步调用一次得到执行？

If I execute this with thousands of files, upload_file will get called thousands of times all at once, and most likely die (or at least struggle). In the synchronous world, we'd create a thread pool and limit it to a certain number of threads. Is there a simple way to limit how many asynchronous calls get executed at once?

推荐答案

像往常一样，我建议Caolan麦克马洪的。

As usual, I recommend Caolan McMahon's async module.

请您 upload_file 函数需要一个回调，因为它的第二个参数：

Make your upload_file function take a callback as it's second parameter:

var async = require("async");

function upload_file(file, callback) {
    // Do funky stuff with file
    callback();
}

var queue = async.queue(upload_file, 10); // Run ten simultaneous uploads

queue.drain = function() {
    console.log("All files are uploaded");
};

// Queue your files for upload
queue.push(files);

queue.concurrency = 20; // Increase to twenty simultaneous uploads

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