Hi, I'm trying to understand how to use coroutines...

# coroutines

[Pacane]

Hi, I'm trying to understand how to use coroutines in my use case... I am using the JVM (and not android). My code doesn't current use coroutines, I'm using Java CompleteableFuture to do async work.

The type of work I'm doing is Fire and Forget type of stuff (I have an infinite while loop doing video/image processing.

I currently have no suspend functions, but I could get my code to work with the GlobalScope.launch function. Now I've read in several places that I should avoid using the GlobalScope. So my question is, how can I create a coroutine scope for a given method (not the main) and still use coroutines for a fire and forget type of work.

I've tried doing something like fun myMethod() = runBlocking { .... } and then inside use CoroutineScope.launch but the code after the launch block is still blocked by the launch block. What could I do to make this work?

[araqnid]

An outer scope can be created at any time, just seeded with a coroutine context: just stick a val coroutineScope = CoroutineScope(EmptyCoroutineContext) in some owning object

[araqnid]

the only other thin you should do is cancel the scope at some appropriate time — so if you already have a close() or stop() method, that’s the time: the object owning the scope is going away, so cancel the scope

[Pacane]

Yes, I do have that, thank you

[araqnid]

alternatively, it sounds like you could just stick this above your while loop and cancel it in a finally block in case of errors breaking the loop?

[Pacane]

and also, what's the difference between the cancel on the Job returned by launch and the coroutine scope's cancel?

[Pacane]

alternatively, it sounds like you could just stick this above your while loop and cancel it in a finally block in case of errors breaking the loop?

[Pacane]

yes that sounds about right

[araqnid]

well, they are different nodes in the Job hierarchy - the launch job will be a child of the scope Job

[araqnid]

CoroutineScope() will add a fresh Job to the EmptyCoroutineContext, given the invocation above

[araqnid]

this does mean that all your jobs are now linked together- if you cancel one of the jobs returned from launch, that will propagate up and then across to its siblings as well

[araqnid]

if that’s not what you want, you should add SupervisorJob() to the context passed to CoroutineScope and then the cancelled child jobs won’t cause armageddon

[araqnid]

that would more closely resemble using GlobalScope (which doesn’t have a Job at all, so all the child launch jobs wouldn’t have anywhere to propagate their failure/cancellation to)

[Pacane]

Awesome, thanks for the explanation 🙂