Node.js - Async.js：并行执行如何工作？ [英] Node.js - Async.js: how does parallel execution work?

问题描述

我想知道并行执行在async.js中是如何工作的

I want to know how parallel execution works in async.js

async = require('async')

async.parallel([
    function(callback){
        for (var i = 0; i < 1000000000; i++) /* Do nothing */;
        console.log("function: 1")
    },
    function(callback){
        console.log("function: 2")
    }
]);

在上面的例子中，我希望获得输出：

In the above example, I expect obtain the output:

功能：2

function: 2

功能：1

但是，控制台抛出反转，发生了什么？谢谢。

but, the console throws the inverse, what is happening? thanks.

推荐答案

你得到了你不想要的答案，因为 async 首先启动函数：1 ，它不会将控制权释放回事件循环。您在函数中没有异步函数：1 。

You get the answer you don't expect because async launches function: 1 first and it doesn't release control back to the event loop. You have no async functions in function: 1.

Node.js是一个单线程异步服务器。如果使用长时间运行的CPU任务阻止事件循环，则在长时间运行的CPU任务完成之前不能调用其他函数。

Node.js is a single-threaded asynchronous server. If you block the event loop with a long running CPU task then no other functions can be called until your long running CPU task finishes.

而不是大的for循环，请尝试发出http请求。例如......

Instead for a big for loop, try making http requests. For example...

async = require('async')
request = require('request')

async.parallel([
    function(callback){
      request("http://google.jp", function(err, response, body) {
        if(err) { console.log(err); callback(true); return; }
        console.log("function: 1")
        callback(false);
      });
    },
    function(callback){
      request("http://google.com", function(err, response, body) {
        if(err) { console.log(err); callback(true); return; }
        console.log("function: 2")
        callback(false);
      });
    }
]);

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