Concurrent Compilation Error

Caching the webpack compiler, introduced in PR #109, causes an error when compiling multiple files concurrently.

This issue is not related to gulp however I ran into it when using gulp to compile my project. I am working with a mono-repo where I have a services directory which contains several microservices. each microservice has its own src directory which contains an index.js.

I use the following code to compile each micro service individually

const gulp = require('gulp')
const compiler = require('webpack')
const webpack = require('webpack-stream')

...

gulp.task('webpack', function () {
  const tasks = getDirectories(`./services`).map((dir) => {
    return gulp.src(join(dir, 'src/index.js'))
      .pipe(webpack(require('./webpack.config.js'), compiler))
      .pipe(gulp.dest(join(dir, 'dist/')))
  })

  return merge(tasks)
})

webpack-stream 5.0.0 works as expected and produces a compiled version of each microservice which is stored in a dist directory alongside its respective src directory.

webpack-stream 5.1.0 introduced caching and reuses the same webpack instance for each compilation task which results in the following error:

ConcurrentCompilationError: You ran Webpack twice. Each instance only supports a single concurrent compilation at a time.

[danieldiekmeier]

I came across the same error and fixed it by downgrading to 5.0, but it would be nice to have the cache working correctly/reliably.

[WillsB3]

I’m also seeing this issue when using webpack-stream in combination with gulp.parallel.