How does Node.js schedule Workers on a limited resource system

Question

I would like to know how to take full advantage of the Worker class in nodejs' worker_threads , specifically, on a 1 or 2 cpu system, do tasks get scheduled better than if I had just blocked in a for-loop in a regular nodejs program (without making use of any worker api)? Are they just delegated to the OS?

Also, can I block inside a Worker? I assumed that's what they are for.

Answer 1

How does Node.js schedule Workers on a limited resource system

Nodejs worker threads use underlying OS threads so worker threads are scheduled by the OS, not by nodejs. If you have more active threads than you have CPU cores, then the underlying OS will time slice (eg share) the cores among the active threads. In general, you shouldn't write a blocked for loop in the main nodejs event loop thread, but for more specifics on that part of the question, we would need to see the actual code you're talking about, what the precise context is and what the alternatives are.

Also, can I block inside a Worker? I assumed that's what they are for.

Yes, you can. It will not have any adverse effect on the main event loop thread. You will, of course, not be able to do anything else in the worker thread while it is blocked. Also, you may want to know that worker threads in nodejs are not lightweight things (in terms of memory usage). Each one comes with a separate V8 interpreter environment. So, in a low resource system, you will have to very carefully plan out your memory usage as nodejs + multiple worker threads do not make for low memory usage.

Keep in mind that each V8 interpreter instance also creates its own thread pool for the libuv engine to use for things like crypto operations and file operations to allow blocking OS system calls to present an asynchronous interface to the JS engine. So, in addition to your Javascript threads, there are also these libuv threads involved in some nodejs APIs.