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0 pointsdmitriid6y ago0 comments

You say no it doesn't and then speak about concurrency models for single-threaded systems. Choose one :)

Node can't not be single-threaded. Because Javascript is. Node.js is single threaded. It has a single event loop in a single thread, and all the "concurrency" is simply queued on that loop. It offloads some tasks to libuv for some system-related tasks but that's it. And the thread pool that libuv creates is very limited.

Anything that doesn't end up in libuv (that is, probably vast majority of user code) will only ever run in one thread... because Javascript is single-threaded hence V8 is single-threaded hence Node.js you get the gist.

And of course, node.js even has a separate documentation section titled "Don't Block the Event Loop (or the Worker Pool)" [1] because it's trivial to block the event loop.

[1] https://nodejs.org/en/docs/guides/dont-block-the-event-loop/

0 pointsdmitriid6y ago0 comments

You say no it doesn't and then speak about concurrency models for single-threaded systems. Choose one :)

And of course, node.js even has a separate documentation section titled "Don't Block the Event Loop (or the Worker Pool)" [1] because it's trivial to block the event loop.

[1] https://nodejs.org/en/docs/guides/dont-block-the-event-loop/

0 comments

4 comments · 2 top-level

willglynn6y ago· 1 in thread

Not OP, but… concurrency is not the same as parallelism. This is an important hair to split:

https://stackoverflow.com/a/24684037/1026671

"Concurrency" doesn't warrant scare quotes even when describing a single threaded program.

It's true that Node.js allows one task to block many others, but that's an implementation detail of Node.js, not a guaranteed result which necessarily applies to any program using only one OS thread. Other programs suffer from analogous starvation/deadlock/livelock/priority inversion problems, but those would be implementation details too, not guaranteed results from using multiple OS threads.

dmitriidOP6y ago

I never said anything about other programs. I never said that other single-threaded programs don't suffer from the same problems. That's is sort of the point. Node.js is single-threaded and, as a result, had all the same problems a single-threaded programs has. And no amount of hand-waving can change that fact.

coddle-hark6y ago· 1 in thread

You’re focusing on single-threadedness like that’s a problem but it’s not. For example, you can run multiple processes on a single core system just fine — even if one of those processes hangs.

AFAIK there’s nothing in the JS language that forces a single-threaded implementation. I think the real reasons that Node is single threaded are a) legacy and more importantly b) a lot of existing code would break if events were dispatched in parallel.

dmitriidOP6y ago

> you can run multiple processes on a single core system just fine — even if one of those processes hangs.

Yes, I can. Node.js doesn't do that.

j / k navigate · click thread line to collapse