What are worker threads?

Q: What are worker threads?

Worker isMainThread parentPort workerData THERE ARE MORE Unlike child_process or cluster, worker_threads can share memory. They do so by transferring ArrayBuffer instances or sharing SharedArrayBuffer instances.

Difficulty: 5/10

worker_threads API, message passing, CPU-bound offloading

The node:worker_threads module enables the use of threads that execute JavaScript in parallel. Workers (threads) are useful for performing CPU-intensive JavaScript operations. They don't help much with I/O-intensive work. The Node.js built-in asynchronous I/O operations are more efficient than Workers can be.

List important properties available on worker_threads module:

1
Worker
2
isMainThread
3
parentPort
4
workerData
5
THERE ARE MORE

Unlike child_process or cluster, worker_threads can share memory. They do so by transferring ArrayBuffer instances or sharing SharedArrayBuffer instances.

Scenario Questions

0-2 years experience

1You need to parse a large CSV file without blocking the event loop. How would you use a Worker thread to accomplish this, and what steps are required to get the parsed data back to the main thread?
2If you create a Worker with `new Worker('./worker.js')` and forget to call `worker.unref()`, what effect does that have on process shutdown?
3What happens if the Worker throws an uncaught exception? How does the main thread observe it?

Follow-up Questions

How would you decide between a Worker and a child process for a given task?
What are the pitfalls of sharing state between the main thread and a Worker?
Can you describe how you would handle errors emitted by a Worker?