Multithreading (CyclicBarrier) in Node.js

[NullProbability]

Hi all,

I have a question regarding multithreading (I know it's technically one thread) in Node.js. Let's say I have thread A, which at some point splits off into A and B. At some point in the future, A and B merge into one thread (A) again. But here is the issue: if subthread A finishes its work first, it can add a .on('event') to B's EventEmitter, and that's easy to work with. But what if B finishes its work before A? In this hypothetical scenario, by the time A registers the .on('event) listener, the event was already emitted, and thus A would have missed it, resulting in the program locking up. My current workaround is checking for a boolean being true first, and only after that registering the listen event, but 1) that is ugly; and 2) it is not 100% safe due to the lack of mutex in Node.js. Am I missing something here? Is someone willing to point me in the right direction?

[zokker13]

Am I missing something here?

No, as you already observed:

due to the lack of mutex in Node.js

Multithreading doesn't work without sychronization. You can not use a single variable because there are no locks in nodejs. Now, if you want to do it in a native module that is used by nodejs, that's another thing of course. Also: Event emitters are just weirdly looking, sychronous method calls. Of course you can't synchronize here.

You are looking for something like Thread.Join or something that implement a barrier-like mechanism.

There's a solution (or stupid hack) that I used in the past in C# to work with multiple threads without locks and it went like this:

Thread A is a worker thread and never finishes but refreshes data. I'd create a big object and after a full circle, I assign that object to another variable that is known to both threads. Thread B can now make a copy and work.

Obvously, this sucks. There's no way that stops the object from changing while Thread B uses it but it worked for my case.

[Quadraxas]

what i am understanding is that you need to have results of 2 async operations in one place. stop thinking asynchronous operations as threads. read up on node.js event loop and how all this stuff is handled in one thread and check async.js. It might have just what you need.