`webpack-dev-server` cannot be killed when spawned with `child_process`

[AaronBeaudoin]

• Operating System: Windows 10.0.17134 Build 17134
• Node Version: 8.11.1
• NPM Version: 5.6.0
• webpack Version: 4.39.0
• webpack-dev-server Version: 3.7.2
• Browser: Not Applicable

• This is a bug
• This is a modification request

Expected Behavior

webpack-dev-server should be killed with childProcess.kill() after spawning it with require("child_process").spawn().

Actual Behavior

webpack-dev-server is orphaned instead of being killed in the above scenario.

Steps to Reproduce

Create a folder with the following package.json:

{
  "name": "webpack-dev-server-process-exit-bug-test",
  "dependencies": {
    "webpack": "^4.39.0",
    "webpack-cli": "^3.3.6",
    "webpack-dev-server": "^3.7.2"
  }
}

Add a test.js file:

const { spawn: spawnProcess } = require("child_process");

let devServerProcess = spawnProcess(
  ".\\node_modules\\.bin\\webpack-dev-server", [],
  { shell: true, stdio: "inherit" });

setTimeout(_ => {
  devServerProcess.kill();
  console.log("Trying to kill webpack-dev-server...");
}, 5000);

Add a src.js file to satisfy the webpack zero-config defaults:

console.log("test");

Run npm i then node test.js and check the running processes on your system. The webpack-dev-server node has not been killed as expected.

Note

This issue still occurs when the stdio option is not supplied to the spawn function.

[alexander-akait]

I think duplicate #1479, we can't kill process when webpack do compilation right now, also it is unsafe for cache

[alexander-akait]

Here explain #1479 (comment)

[AaronBeaudoin]

If I comment out the setTimeout call in my code above and instead just use [ctrl]+[c] manually after about 5 seconds then all processes seem to be killed properly. According to the issue you referenced, shouldn't this problem still be occurring is such a scenario?

[alexander-akait]

@AaronBeaudoin try to use 10 seconds or more

[AaronBeaudoin]

If the point is to ensure that compiling has completed before trying to kill the process then it's irrelevant. I get the Compiled successfully. message after about a second or two. Therefore the process is definitely not getting killed in the middle of compilation.

[AaronBeaudoin]

Also it seems that using the fork function instead of the spawn function solves the issue as well:

const { fork: forkProcess } = require("child_process");

let devServerProcess = forkProcess(
  ".\\node_modules\\webpack-dev-server\\bin\\webpack-dev-server.js", []);

setTimeout(_ => {
  devServerProcess.kill();
  console.log("Trying to kill webpack-dev-server...");
}, 5000);

[alexander-akait]

@AaronBeaudoin thanks for investigation, we look on this in near future, anyway feel free to debug and send a PR with fix

[AaronBeaudoin]

In case it helps, it seems that when spawning processes with spawn and the shell option is set to true, an invisible cmd.exe window is created with the process running inside of it. I found that when calling childProcess.kill() the cmd.exe window is properly killed; it's just the webpack-dev-server process that was inside of it which is left still running.

[alexander-akait]

@AaronBeaudoin maybe it is only on windows, can you sty this on linux?

[xiaoyouyu]

Is there a solution?

[xiaoyouyu]

var exec = require('child_process').execSync; exec(’webpack-dev-server --inline --progress --config build/webpack.dev.conf.js --useLocalIp‘, { stdio: 'inherit' })

@evilebottnawi
Please, How to kill this process？

[alexander-akait]

@xiaoyouyu better use execa and use something like this:

setTimeout(() => {
	subprocess.kill('SIGTERM', {
		forceKillAfterTimeout: 2000
	});
}, 1000);

[ifedyukin]

In my case I've solved same issue by next steps:

Firstly added Windows-specific code to emit SIGINT process event.

const rl = require('readline');

if (/^win/.test(process.platform)) {
  rl.createInterface({
      input: process.stdin,
      output: process.stdout
  }).on('SIGINT', () => process.emit('SIGINT'));
}

Secondly added specific code to kill process on different OS.

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

function killChildProcess(childProcess) {
    if (/^win/.test(process.platform)) {
        execSync(`taskkill /pid ${childProcess.pid} /f /t`);
    } else {
        process.kill(childProcess.pid);
    }
};

[xiaoyouyu]

In my case I've solved same issue by next steps:

Firstly added Windows-specific code to emit SIGINT process event.

const rl = require('readline');

if (/^win/.test(process.platform)) {
  rl.createInterface({
      input: process.stdin,
      output: process.stdout
  }).on('SIGINT', () => process.emit('SIGINT'));
}

Secondly added specific code to kill process on different OS.

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

function killChildProcess(childProcess) {
    if (/^win/.test(process.platform)) {
        execSync(`taskkill /pid ${childProcess.pid} /f /t`);
    } else {
        process.kill(childProcess.pid);
    }
};

How to get the childProcess