Node.js异步文件I / O.(Node.js Asynchronous File I/O)

 我是Node.js的新手，最近了解了fs模块。 我对异步与同步文件i / o有点困惑。 
 
 考虑以下测试： 
 
var fs = require('fs');

var txtfile = 'async.txt';
var buffer1 = Buffer(1024);
var buffer2 = '1234567890';

fs.appendFile(txtfile, buffer1, function(err) {
    if (err) { throw err };
    console.log('appended buffer1');
});

fs.appendFile(txtfile, buffer2, function(err) {
    if (err) { throw err };
    console.log('appended buffer2');
});
 
 大约一半的时间我运行它，它appended buffer2在appended buffer1之前打印appended buffer1 。 但是当我打开文本文件时，数据总是看起来是正确的顺序 - 来自Buffer(1024)的一堆垃圾后跟1234567890 。 我原本期望反向或乱七八糟的混乱。 
 
 这里发生了什么？ 难道我做错了什么？ 是否有某种维持秩序的低级i / o队列？ 
 
 我已经看到一些关于文件系统与Node的i / o差异的讨论; 我在Mac上，如果这有任何区别。 

I'm new to Node.js and recently learned about the fs module. I'm a little confused about asynchronous vs. synchronous file i/o. 
 
Consider the following test:
 
var fs = require('fs');

var txtfile = 'async.txt';
var buffer1 = Buffer(1024);
var buffer2 = '1234567890';

fs.appendFile(txtfile, buffer1, function(err) {
    if (err) { throw err };
    console.log('appended buffer1');
});

fs.appendFile(txtfile, buffer2, function(err) {
    if (err) { throw err };
    console.log('appended buffer2');
});
 
About half the time when I run this, it prints appended buffer2 before appended buffer1. But when I open the text file, the data always appears to be in the right order - a bunch of garbage from Buffer(1024) followed by 1234567890. I would have expected the reverse or a jumbled mess.
 
What's going on here? Am I doing something wrong? Is there some kind of lower-level i/o queue that maintains order?
 
I've seen some talk about filesystem i/o differences with Node; I'm on a Mac if that makes any difference.

原文：https://stackoverflow.com/questions/23427430