parallelism not work

[keenwon]

Bug report

What is the current behavior?

https://webpack.docschina.org/configuration/configuration-types/#parallelism

parallelism does not work

If the current behavior is a bug, please provide the steps to reproduce.

index.js

console.log(`test ${Math.random()}`)
console.log(`test ${Math.random()}`)
console.log(`test ${Math.random()}`)
console.log(`test ${Math.random()}`)
console.log(`test ${Math.random()}`)
console.log(`test ${Math.random()}`)

webpack.config.js

const path = require("path")
const SimpleProgressWebpackPlugin = require("simple-progress-webpack-plugin")

const configs = []

for (let i = 0; i < 3; i++) {
  configs.push({
    name: `build${i}`,
    entry: "./index",
    output: {
      path: path.join(__dirname, "dist"),
      filename: `build${i}.js`,
    },
    plugins: [
      new SimpleProgressWebpackPlugin({
        name: `build${i}`,
        format: "simple",
      }),
    ],
  })
}

module.exports = configs
module.exports.parallelism = 1

output:

build0

  ❯ Compile modules
build1

  ❯ Compile modules
build2

  ❯ Compile modules
  ❯ Build modules
  ❯ Build modules
  ❯ Build modules
  ❯ Optimize modules
  ❯ Optimize modules
  ❯ Optimize modules
  ❯ Emit files

Finished after 0.244 seconds.

  ❯ Emit files

Finished after 0.242 seconds.

  ❯ Emit files

Finished after 0.254 seconds.

build0
  ❯ Emit files

Finished after 0.000 seconds.

build1
  ❯ Emit files

Finished after 0.000 seconds.

build2
  ❯ Emit files

Finished after 0.001 seconds.

build0:
  asset build0.js 222 bytes [compared for emit] [minimized] (name: main)
  ./index.js 222 bytes [built] [code generated]

  WARNING in configuration
  The 'mode' option has not been set, webpack will fallback to 'production' for this value.
  Set 'mode' option to 'development' or 'production' to enable defaults for each environment.
  You can also set it to 'none' to disable any default behavior. Learn more: https://webpack.js.org/configuration/mode/

  build0 (webpack 5.47.1) compiled with 1 warning in 237 ms

build1:
  asset build1.js 222 bytes [compared for emit] [minimized] (name: main)
  ./index.js 222 bytes [built] [code generated]

  WARNING in configuration
  The 'mode' option has not been set, webpack will fallback to 'production' for this value.
  Set 'mode' option to 'development' or 'production' to enable defaults for each environment.
  You can also set it to 'none' to disable any default behavior. Learn more: https://webpack.js.org/configuration/mode/

  build1 (webpack 5.47.1) compiled with 1 warning in 230 ms

build2:
  asset build2.js 222 bytes [compared for emit] [minimized] (name: main)
  ./index.js 222 bytes [built] [code generated]

  WARNING in configuration
  The 'mode' option has not been set, webpack will fallback to 'production' for this value.
  Set 'mode' option to 'development' or 'production' to enable defaults for each environment.
  You can also set it to 'none' to disable any default behavior. Learn more: https://webpack.js.org/configuration/mode/

  build2 (webpack 5.47.1) compiled with 1 warning in 215 ms

What is the expected behavior?

Other relevant information:
webpack version: 5.47.1
Node.js version: v14.16.1
Operating System: ubuntu
Additional tools: "webpack-cli": "^4.7.2"

[webpack-bot]

For maintainers only:

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• webpack-5
• bug
• critical-bug
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• question

[alexander-akait]

Expected, it is not about parallels execution (multi threading) of compilers, it is more about concurrency, name is m slinging due historical reasons, maybe we rename it in future, https://webpack.js.org/configuration/other-options/#parallelism, an issue for multi threading already exists

[sokra]

It's about concurrency, but that doesn't seem to work, as all compilers execute concurrently which they shouldn't do. I guess that's not correctly passed by webpack-cli

[alexander-akait]

WIP on fix