threads

What is threads?

The 'threads' npm package provides a simple and efficient way to create and manage threads (or worker threads) in Node.js. It allows you to run JavaScript code in parallel, taking advantage of multi-core processors to improve performance for CPU-intensive tasks.

What are threads's main functionalities?

Creating a Worker

This feature allows you to create a new worker thread by spawning a worker from a separate file ('./worker'). The worker can then execute functions in parallel to the main thread.

const { spawn, Thread, Worker } = require('threads');

(async () => {
  const worker = await spawn(new Worker('./worker'));
  console.log(await worker.someFunction());
  await Thread.terminate(worker);
})();

Communicating with Workers

This feature demonstrates how to send data to a worker and receive results back. The worker can process the data and return the result to the main thread.

const { spawn, Thread, Worker } = require('threads');

(async () => {
  const worker = await spawn(new Worker('./worker'));
  const result = await worker.someFunction('data');
  console.log(result);
  await Thread.terminate(worker);
})();

Error Handling in Workers

This feature shows how to handle errors that occur within worker threads. By using try-catch blocks, you can catch and handle errors gracefully.

const { spawn, Thread, Worker } = require('threads');

(async () => {
  try {
    const worker = await spawn(new Worker('./worker'));
    await worker.someFunctionThatMightFail();
  } catch (error) {
    console.error('Worker error:', error);
  } finally {
    await Thread.terminate(worker);
  }
})();

Other packages similar to threads

jest-worker

'jest-worker' is a package developed by Facebook for parallelizing tasks in Node.js. It is commonly used in the Jest testing framework to run tests in parallel. While it provides similar functionality to 'threads', it is more specialized for use cases involving task parallelization in testing environments.

piscina

'piscina' is a fast, efficient worker thread pool implementation for Node.js. It allows you to manage a pool of worker threads to handle multiple tasks concurrently. 'piscina' is designed for high performance and scalability, making it a good alternative to 'threads' for more complex parallel processing needs.

README

threads

Offload CPU-intensive tasks to worker threads in node.js, web browsers and electron using one uniform API.

Uses web workers in the browser, worker_threads in node 12+ and tiny-worker in node 8 to 11.

Features

• Speed up code by parallel processing
• Keep UI responsive by offloading work from rendering thread
• First-class support for async functions & observables
• Manage bulk task executions with thread pools
• Works great with webpack

Version 0.x

You can find the old version 0.12 of threads.js on the v0 branch. All the content on this page refers to version 1.0 which is a rewrite of the library with a whole new API.

Installation

npm install threads tiny-worker

You only need to install the tiny-worker package to support node.js < 12. It's an optional dependency and used as a fallback if worker_threads are not available.

Run on node.js

Running code using threads.js in node works out of the box.

Note that we wrap the native Worker, so new Worker("./foo/bar") will resolve the path relative to the module that calls it, not relative to the current working directory.

That aligns it with the behavior when bundling the code with webpack or parcel.

Webpack build setup

Webpack config

Use with the threads-plugin. It will transparently detect all new Worker("./unbundled-path") expressions, bundles the worker code and replaces the new Worker(...) path with the worker bundle path, so you don't need to explicitly use the worker-loader or define extra entry points.

  npm install -D threads-plugin

Then add it to your webpack.config.js:

+ const ThreadsPlugin = require('threads-plugin');

  module.exports = {
    // ...
    plugins: [
+     new ThreadsPlugin()
    ]
    // ...
  }

Node.js bundles

If you are using webpack to create a bundle that will be run in node (webpack config target: "node"), you also need to specify that the tiny-worker package used for node < 12 should not be bundled:

  module.exports = {
    // ...
+   externals: {
+     "tiny-worker": "tiny-worker"
+   }
    // ...
}

Make sure that tiny-worker is listed in your package.json dependencies in that case.

When using TypeScript

Make sure the TypeScript compiler keeps the import / export statements intact, so webpack resolves them. Otherwise the threads-plugin won't be able to do its job.

  module.exports = {
    // ...
    module: {
      rules: [
        {
          test: /\.ts$/,
          loader: "ts-loader",
+         options: {
+           compilerOptions: {
+             module: "esnext"
+           }
+         }
        }
      ]
    },
    // ...
  }

Parcel bundler setup

You need to import threads/register once at the beginning of your application code (in the master code, not in the workers):

  import { spawn } from "threads"
+ import "threads/register"

  // ...

  const work = await spawn(new Worker("./worker"))

This registers the library's Worker implementation for your platform as the global Worker. This is necessary, since you cannot import { Worker } from "threads" or Parcel won't recognize new Worker() as a web worker anymore.

Be aware that this might affect any code that tries to instantiate a normal web worker Worker and now instead instantiates a threads.js Worker. The threads.js Worker is just a web worker with some sugar on top, but that sugar might have unexpected side effects on third-party libraries.

Everything else should work out of the box.

Getting Started

Basics

// master.js
import { spawn, Thread, Worker } from "threads"

async function main() {
  const add = await spawn(new Worker("./workers/add"))
  const sum = await add(2, 3)

  console.log(`2 + 3 = ${sum}`)

  await Thread.terminate(sum)
}

main().catch(console.error)

// workers/add.js
import { expose } from "threads/worker"

expose(function add(a, b) {
  return a + b
})

spawn()

The return value of add() in the master code depends on the add() return value in the worker:

If the function returns a promise or an observable then you can just use the return value as such in the master code. If the function returns a primitive value, expect the master function to return a promise resolving to that value.

expose()

Use expose() to make either a function or an object callable from the master thread.

In case of exposing an object, spawn() will asynchronously return an object exposing all the object's functions, following the same rules as functions directly expose()-ed.

Usage

Find the full documentation on the website:

• Introduction
• Basics
• Observables
• Thread pool
• Transferable objects
• Thread events

Debug

We are using the debug package to provide opt-in debug logging. All the package's debug messages have a scope starting with threads:, with different sub-scopes:

• threads:master:messages
• threads:master:spawn
• threads:master:thread-utils
• threads:pool:${poolName || poolID}

Set it to DEBUG=threads:* to enable all the library's debug logging. To run its tests with full debug logging, for instance:

DEBUG=threads:* npm test

License

MIT