Option to limit number of processes/threads/fds

[vicary]

Feature motivation

My team is using serverless-webpack to bundle ~100-ish Lambda functions at the same time, due to constraints in serverless-appsync-plugin we cannot split them into multiple batches, and with webpack + ts-loader alone it is impossible to bundle them all at once.

This module opens up the possibility to keep the type checking, but we quickly hit another problem. i.e. With 100 forked processes it drained the fd limit in no time.

While it is possible to raise such limit to millions for one machine, the development cycle becomes exponentially complicated when it comes to CI/CD in containers.

Feature description

In webpack/webpack@9cb4225 webpack itself limits how many files it opens each time, but fork-ts-checker-webpack-plugin multiplies the limit of 15 by the total number of functions to be bundled.

It would be great if there is an option, or at least a sane default, to limit the total number of threads/forked processes.

Feature implementation

Maintain the number of active forks, delaying further forking until earlier child processes is finished, packages like p-limit is worth considering.

[piotr-oles]

Hi @vicary

I think it's not a common issue so I wouldn't like to implement this logic in the plugin. Instead, I could modify the start hook on the alpha branch to provide AsyncSeriesWaterfallHook. Then you could tap into this hook and add awaiting logic that suits your case :)

Is it something that would help you?

[piotr-oles]

This is a pseudo-code that I came up:

import ForkTsCheckerWebpackPlugin from 'fork-ts-checker-webpack-plugin';
import { Limit } from 'p-limit';

interface LimitForkTsCheckerWorkersWebpackPluginOptions {
  limit: Limit;
}

class LimitForkTsCheckerWorkersWebpackPlugin implements webpack.Plugin {
  constructor(private readonly options: LimitForkTsCheckerWorkersWebpackPluginOptions) {}

  apply(compiler: webpack.Compiler) {
    const hooks = ForkTsCheckerWebpackPlugin.getCompilerHooks(compiler);

    // intercept service starting hook
    hooks.start.tapPromise('LimitForkTsCheckerWorkersWebpackPluginOptions', this.options.limit((changes) => changes));
  }
}

export = LimitForkTsCheckerWorkersWebpackPlugin;

and usage:

// shared/limit.js
const pLimit = require('p-limit');
const limit = pLimit(10);

module.exports = limit;

// webpack.config.js
const limit = require('shared/limit');
const ForkTsCheckerWebpackPlugin = require('fork-ts-checker-webpack-plugin');
const LimitForkTsCheckerWorkersWebpackPlugin = require('shared/plugin/LimitForkTsCheckerWorkersWebpackPlugin');

module.exports = {
   // ...
  plugins: [
    new ForkTsCheckerWebpackPlugin(),
    new LimitForkTsCheckerWorkersWebpackPlugin({ limit })
  ]
  // ...
};

[vicary]

Hi @piotr-oles,

Thanks for the quick reply.

Haven't worked with plugin hooks yet, do you mean I can control each processes with something like the following?

const forkTsCheckerWebpackPlugin = new ForkTsCheckerWebpackPlugin();
let activeCount = 0;
const resolveFn = [];

forkTsCheckerWebpackPlugin.hooks.serviceBeforeStart.tapPromise("throttlePlugin", new Promise((resolve, reject) => {
  if (activeCount < 10) {
    resolve();
    activeCount++;
  } else {
    resolveFns.push(resolve);
  }
}));

forkTsCheckerWebpackPlugin.hooks.done.tap("throttlePlugin", () => {
  const resolve = resolveFns.shift();
  if (resolve) {
    resolve();
  } else {
    activeCount--;
  }
});

This looks like the current AsyncSeriesHook in serviceBeforeStart and SyncHook in done already works.

Am I getting it correctly?

[vicary]

Oh wow thanks for the sample code! So I have to make my own plugin to tap into those hooks, right?

[piotr-oles]

I think it's the most convenient way to do this :) You can also manually get the compiler instance but this means that you would have to use webpack's Node.js API (because you don't have a compiler instance when you just export the configuration).

The pseudo-code I sent you is for the alpha branch - https://github.com/TypeStrong/fork-ts-checker-webpack-plugin/tree/alpha :) I don't want to add new features to the current stable version. It will be maintained only for critical bug fixes, new features will be merged to the alpha branch which is a result of a complete rewrite of the plugin #404 :)

[vicary]

Sounds great!

Just wanna make sure no unnecessary works on your side, does the hook serviceBeforeStart do the job?

[piotr-oles]

Yes, it should work :)

[piotr-oles]

Please let me know when you implement it if it worked 😃

[piotr-oles]

🎉 This issue has been resolved in version 5.0.0-alpha.9 🎉

The release is available on:

• npm package (@alpha dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[vicary]

Yes, it worked to a certain degree, definitely prevented the EMFILE error. Now it only explodes at heap size, which is solved in this PR serverless-heaven/serverless-webpack#517.

Really thanks for the help!