轻松实现并行机制, 只要异步即可.下面是并行统计一个目录下所有文件的单词数.

word_count.js

/*
轻松实现并行机制,统计单词个数

目录结构如下：
├── word_count.js
└── text
    ├── a.txt
    ├── b.txt
    └── c.txt

> node word_count.js
beginman: 1
hi: 2
jack: 2
good: 3
my: 1

*/

var fs = require('fs'),
    completedTasks = 0,
    tasks = [],
    wordCounts = {},
    filesDir = './text';

function checkIfComplete(){
    completedTasks++;
    if( completedTasks == tasks.length) {
        for(var index in wordCounts) {
            console.log(index + ': ' + wordCounts[index]);
        }
    }
}

function countWord(text) {
    var words = text.toString().toLowerCase().split(/\W+/).sort();
    for (var index in words) {
        var word = words[index];
        if (word) {
            wordCounts[word] = wordCounts[word] ? wordCounts[word] + 1 : 1;
        }
    }
}

fs.readdir(filesDir, function (err, files) {
    if (err) throw err;
    for(var index in files) {
        var filePath = filesDir + '/' + files[index];
        // 定义任务,由于readFile是异步的,则可并行执行
        var task = (function (file) {
            return function () {
                fs.readFile(file, function (err, data) {
                    if (err) throw err;
                    countWord(data);
                    checkIfComplete();
                })
            }
        })(filePath);

        // 把所有任务都添加到数组中
        tasks.push(task);
    }

    // 开始并行执行所有任务
    for (var task in tasks) {
        tasks[task]();
    }
});