I was messing around with launching coroutines inside an async parent coroutine and the effects on t...

# coroutines

[Tristan Hamilton]

I was messing around with launching coroutines inside an async parent coroutine and the effects on their completion when cancelling that parent scope. I wanted to see could they still be cancelled early if passed as a lambda to a function that would wrap them in a parent coroutine. Doesn't seem to work as I expected.
Here's a gist - https://gist.github.com/Munzey/212f38879039987a4c819c53d1d393cd
maybe its just something one should never do, but maybe someone can explain to me why it doesn't work the way I thought it would 🙂 cheers!

[Marc Knaup]

The name parentScope is confusing. You’re passing the child, not the parent.

[Marc Knaup]

It works as expected.
coroutineScopeWrapper returns immediately because two two launch are executed in the real parent scope of runBlocking and thus the scope of async doesn’t need to wait for them.

[Tristan Hamilton]

oh my bad maybe I'm misunderstanding.
In my head when I call the async builder, that is the "parent" coroutine, and so from there im passing that down

[Marc Knaup]

runBlocking is the topmost scope.
coroutineScope is a child of runBlocking (more or less).
async is a child of coroutineScope.

And the launch in your wrapper use the CoroutineScope of runBlocking so they’re direct children of it.

[Marc Knaup]

launch basically means [e-mail] in your example.

[Marc Knaup]

Nonetheless, cancel() doesn’t cancel. WTF 😄

[Tristan Hamilton]

Thanks for this explanation, really helpful! I thought that coroutineScope provides a different Job and that the launches were "tied" to it, but I guess they still have the same context which is runBlocking?
So to make this cancel the way I expect, would I need to define a new scope in coroutineScopeWrapper instead?

[Marc Knaup]

launch is tied to it. But you don’t give the launch invocation the CoroutineScope of the async.

[Marc Knaup]

I’ve added a comment to fix the scope:
https://gist.github.com/Munzey/212f38879039987a4c819c53d1d393cd#gistcomment-3620551

[Marc Knaup]

I’ve added another comment.

[Tristan Hamilton]

ah thanks a lot 🙂