search
HomeWeb Front-endJS TutorialIntroduction to Node.js child processes and applications
Introduction to Node.js child processes and applicationsJun 30, 2018 pm 02:57 PM
nodenodejschild process

This article mainly introduces a brief discussion of Node.js sub-processes and application scenarios. The content is quite good. I will share it with you now and give it as a reference.

Background

Since ons (Alibaba Cloud RocketMQ package) is encapsulated based on C++, it does not support the instantiation of multiple producers and consumers in a single process. Or, in order to solve this problem, Node.js child process is used.

Pits encountered during use

Release: After process management closes the main process, the child process becomes an operating system process (pid is 1)

Several solutions

Treat the child process as an independent running process, record the pid, and process management to close the main process and close the child process at the same time when publishing

The main process listens to the shutdown event and actively closes its own child processes

Type of child process

  1. spawn: Execute command

  2. exec: execute command (new shell)

  3. execFile: execute file

  4. fork: execute file

Common events for child processes

  1. exit

  2. close

  3. error

  4. message

There is a difference between close and exit. close is when the data stream is closed. The event is triggered when the child process exits. exit is the event that is triggered when the child process exits. Because multiple child processes can share the same data stream, the close event may not necessarily be triggered when a child process exits, because there are other child processes using the data stream at this time.

Subprocess data flow

  1. stdin

  2. stdout

  3. stderr

#Because the main process is the starting point, the data flow of the sub-process is opposite to the conventionally understood data flow direction. stdin: write stream, stdout, stderr: Read stream.

spawn

spawn(command[, args][, options])

Execute a command and return various execution results through the data data stream.

Basic usage

const { spawn } = require('child_process');

const child = spawn('find', [ '.', '-type', 'f' ]);
child.stdout.on('data', (data) => {
  console.log(`child stdout:\n${data}`);
});

child.stderr.on('data', (data) => {
  console.error(`child stderr:\n${data}`);
});

child.on('exit', (code, signal) => {
  console.log(`child process exit with: code $[code], signal: ${signal}`);
});

Common parameters

{
  cwd: String,
  env: Object,
  stdio: Array | String,
  detached: Boolean,
  shell: Boolean,
  uid: Number,
  gid: Number
}

Focus on the detached attribute. Setting detached to true is to prepare the child process to run independently. The specific behavior of the child process is related to the operating system. Different systems behave differently. The Windows system child process will have its own console window, and the POSIX system child process will become the new process group and session leader.

At this time, the child process is not completely independent. The running results of the child process will be displayed on the data stream set by the main process, and the exit of the main process will affect the operation of the child process. When stdio is set to ignore and child.unref(); is called, the child process begins to truly run independently, and the main process can exit independently.

#exec

exec(command[, options][, callback])

Execute a command and return the result through the callback parameter. The part will be cached before the command is executed. results into system memory.

const { exec } = require('child_process');

exec('find . -type f | wc -l', (err, stdout, stderr) => {
  if (err) {
    console.error(`exec error: ${err}`);
    return;
  }

  console.log(`Number of files ${stdout}`);
});

The best of both worlds - spawn instead of exec

Since the result of exec is returned once, before returning Cache in memory, so when the output of the executed shell command is too large, using exec to execute the command cannot complete our work as expected. At this time, we can use spawn instead of exec to execute the shell command.

const { spawn } = require('child_process');

const child = spawn('find . -type f | wc -l', {
  stdio: 'inherit',
  shell: true
});

child.stdout.on('data', (data) => {
  console.log(`child stdout:\n${data}`);
});

child.stderr.on('data', (data) => {
  console.error(`child stderr:\n${data}`);
});

child.on('exit', (code, signal) => {
  console.log(`child process exit with: code $[code], signal: ${signal}`);
});

execFile

child_process.execFile(file[, args][, options][, callback])

Execute a file

The function is basically the same as exec. The difference is that it executes a script file with a given path and directly creates a new process instead of creating a shell environment and then running the script, which is relatively lightweight and more efficient. . However, in Windows systems, files such as .cmd and .bat cannot be run directly. This means that execFile will not work. You can use spawn and exec instead.

#fork

child_process.fork(modulePath[, args][, options])

Execute a Node.js file

// parent.js

const { fork } = require('child_process');

const child = fork('child.js');

child.on('message', (msg) => {
  console.log('Message from child', msg);
});

child.send({ hello: 'world' });

// child.js

process.on('message', (msg) => {
  console.log('Message from parent:', msg);
});

let counter = 0;

setInterval(() => {
  process.send({ counter: counter++ });
}, 3000);

fork is actually a special form of spawn, which fixes the spawn Node.js process and establishes a communication channel between the master and child processes to allow the master and child processes to Event-based communication can be done using the process module.

Subprocess usage scenarios

  1. Computationally intensive systems

  2. Front-end build tools utilize multi-core CPUs Parallel computing, improve construction efficiency

  3. Process management tools, such as: some functions in PM2

The above is the entire content of this article, I hope it will be helpful to everyone Learning will be helpful. For more related content, please pay attention to the PHP Chinese website!

Related recommendations:

Introduction to Webpack optimization configuration to narrow file search scope

The Request module in Node.js handles HTTP Introduction to the use of protocol requests

Parsing of custom error types under Node.js

The above is the detailed content of Introduction to Node.js child processes and applications. For more information, please follow other related articles on the PHP Chinese website!

Statement
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn
Vercel是什么?怎么部署Node服务?Vercel是什么?怎么部署Node服务?May 07, 2022 pm 09:34 PM

Vercel是什么?本篇文章带大家了解一下Vercel,并介绍一下在Vercel中部署 Node 服务的方法,希望对大家有所帮助!

node.js gm是什么node.js gm是什么Jul 12, 2022 pm 06:28 PM

gm是基于node.js的图片处理插件,它封装了图片处理工具GraphicsMagick(GM)和ImageMagick(IM),可使用spawn的方式调用。gm插件不是node默认安装的,需执行“npm install gm -S”进行安装才可使用。

火了!新的JavaScript运行时:Bun,性能完爆Node火了!新的JavaScript运行时:Bun,性能完爆NodeJul 15, 2022 pm 02:03 PM

今天跟大家介绍一个最新开源的 javaScript 运行时:Bun.js。比 Node.js 快三倍,新 JavaScript 运行时 Bun 火了!

nodejs中lts是什么意思nodejs中lts是什么意思Jun 29, 2022 pm 03:30 PM

在nodejs中,lts是长期支持的意思,是“Long Time Support”的缩写;Node有奇数版本和偶数版本两条发布流程线,当一个奇数版本发布后,最近的一个偶数版本会立即进入LTS维护计划,一直持续18个月,在之后会有12个月的延长维护期,lts期间可以支持“bug fix”变更。

聊聊Node.js中的多进程和多线程聊聊Node.js中的多进程和多线程Jul 25, 2022 pm 07:45 PM

大家都知道 Node.js 是单线程的,却不知它也提供了多进(线)程模块来加速处理一些特殊任务,本文便带领大家了解下 Node.js 的多进(线)程,希望对大家有所帮助!

node爬取数据实例:聊聊怎么抓取小说章节node爬取数据实例:聊聊怎么抓取小说章节May 02, 2022 am 10:00 AM

node怎么爬取数据?下面本篇文章给大家分享一个node爬虫实例,聊聊利用node抓取小说章节的方法,希望对大家有所帮助!

深入浅析Nodejs中的net模块深入浅析Nodejs中的net模块Apr 11, 2022 pm 08:40 PM

本篇文章带大家带大家了解一下Nodejs中的net模块,希望对大家有所帮助!

怎么获取Node性能监控指标?获取方法分享怎么获取Node性能监控指标?获取方法分享Apr 19, 2022 pm 09:25 PM

怎么获取Node性能监控指标?本篇文章来和大家聊聊Node性能监控指标获取方法,希望对大家有所帮助!

See all articles

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

AI Hentai Generator

AI Hentai Generator

Generate AI Hentai for free.

Hot Article

R.E.P.O. Energy Crystals Explained and What They Do (Yellow Crystal)
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. Best Graphic Settings
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌
R.E.P.O. How to Fix Audio if You Can't Hear Anyone
3 weeks agoBy尊渡假赌尊渡假赌尊渡假赌

Hot Tools

WebStorm Mac version

WebStorm Mac version

Useful JavaScript development tools

SAP NetWeaver Server Adapter for Eclipse

SAP NetWeaver Server Adapter for Eclipse

Integrate Eclipse with SAP NetWeaver application server.

MantisBT

MantisBT

Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Dreamweaver Mac version

Dreamweaver Mac version

Visual web development tools