On: Concurrent JavaScript: It can work

[pizlonator]

Even loop is not concurrency.

Just because concurrency and parallelism are different does not meant that concurrency and event loops are the same.

[skybrian → pizlonator]

Creating async tasks that can run concurrently and deliver progress via events is a concurrency model.

[loftyal → pizlonator]

How? Explain please. https://en.wikipedia.org/wiki/Concurrency_(computer_science)

"order-independent components", which makes sense for the Event loop.

[pizlonator → loftyal]

I draw the line at whether the interleaving granule is under the programmer’s control or not.

For example, I can say that when a task executes on an event loop, no other tasks are executing concurrently to it because the event loop executes tasks sequentially.

[loftyal → pizlonator]

Ok you draw the line there, but definitions are supposed to be commonly understood, that's how language works...

[pizlonator → loftyal]

Yeah, I agree it would be better if people in the event loop community learned to use the word “concurrency” correctly.

[christophilus → pizlonator]

You can build concurrency on the event-loop, though, which is what the OP was probably referring to.

[pizlonator → christophilus]

Not quite. Consider a component in your code that does this:

    for (let blah of things)
        foo(blah);

In an event loop, if things has a lot of stuff in it, this can block the event loop. Other things in the event loop won't be able to run until this completes.

With threads, this just works.

[enoah_netzach → pizlonator]

That is parallelism, not concurrency.

Concurrency: two functions can run one after the other while they are non blocking for the callers (e.g. hyperthreading).

Parallelism: two functions can run at the same time (e.g. multiple processors).

[pizlonator → enoah_netzach]

Your definition of concurrency is not correct. Concurrency usually implies that the work is chopped up into very small interleavable bits. A while function call with a loop of unbounded length being the default granule of interleaving is definitely not part of the definition of concurrency.

The term "concurrency" subsumes both event loop style concurrency and two-cores-running-code-at-the-same time concurrency.

[Jtsummers → pizlonator]

Yes, it is. The JavaScript event loop is a very lazy scheduler than does no preemption. It's a very primitive concurrency model. It's up to the users of the language to break their tasks down into sufficiently small components or yield to allow for interleaving of work.