On the JVM, what's the preferred way to "find and ...

# coroutines

[Don Mitchell]

On the JVM, what's the preferred way to "find and select a coroutine scope" from a top-level function that isn't main? e.g., when implementing com.github.ajalt.clikt.core.CoreCliktCommand#run ?

You can't

CoroutineScope().launch {
...
}

as there's nothing to stop the process from exiting and the container from shutting down before it does anything (there's no containing scope). You can't call join on that bc there's no suspend context.

I've been wantonly using runBlocking but I know that's not the preferred pattern. What I don't grok is what is the preferred pattern? (NOTE, this is a long-running headless batch service; so, there's no UI so MainScope makes no sense, coroutineScope is not allowed bc it's not a suspend context, GlobalScope has the same problem as CoroutineScope() , neither of these exist: lifecycleScope, viewModelScope)

[kevin.cianfarini]

run blocking is perfectly fine to use if you KNOW that the synchronous function being invoked won't be invoked from a coroutine.

If your call stack looks something like:

• run blocking
• Click command
• Main
Then that's totally fine.

[Sam]

Oh no, "find and select a coroutine scope" is one of my lines, isn't it 😄

[Sam]

In Ch3 of the book I have this tip:
> Some frameworks, including Spring, Quarkus, and Micronaut, have special support for coroutines, and let you add the suspend modifier directly to your controller methods. Check the documentation for your chosen tool to see what options you have.
I think Clikt is an example where this tip applies quite well: if I'm understanding the docs correctly, it looks like you can swap your CoreCliktCommand for a SuspendingCliktCommand. It has a suspending run() function, inside which you'd be able to use the coroutineScope() function.

[Sam]

I agree with Kevin that runBlocking would also likely be okay in that specific scenario too, since this is essentially an entrypoint

[Joffrey]

You're right about Clikt. We use SuspendingCliktCommand in Amper so we have suspending entrypoints. You just have to make sure all of them are suspending, it's not possible to mix.

[Joffrey]

https://github.com/JetBrains/amper/blob/release%2F0.6/sources%2Fcli%2Fsrc%2Forg%2Fjetbrains%2Famper%2Fcli%2Fcommands%2FRootCommand.kt

[Joffrey]

We used to use runBlocking when Clikt didn't have that, and I agree with Sam and Kevin that this is one of the rare cases where runBlocking is fine