Hello is there any way to run two coroutines in parallel and then return the first result that finis...

# coroutines

[Pablo]

Hello is there any way to run two coroutines in parallel and then return the first result that finishes first?
I've thought to use Job and then if the first finishes first cancel the second Job to stop doing the work, also I think the way to do it is using launch{} right? Instead of async {}

[simon.vergauwen]

You can use select for this, or something like raceN from Arrow Fx.

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.selects/select.html

https://arrow-kt.io/docs/fx/parallel/#racing-parallel-operations

[Pablo]

Can you provide a pseudo example how does `select`works?

[Pablo]

I've found this but don't know if it's what I want because I guess it waits for all coroutines to finish
https://stackoverflow.com/questions/69045114/return-a-specific-value-only-of-the-faster-coroutine

[simon.vergauwen]

Here is the impl of raceN in Arrow which is build on top of select.

https://github.com/arrow-kt/arrow/blob/706a48f2fd9fdf07b4bb3f982122a9e42c29c9b5/ar[…]x-coroutines/src/commonMain/kotlin/arrow/fx/coroutines/Race2.kt

[Pablo]

suspend fun getFaster(): Int = coroutineScope {
    select<Int> {
        async { getFromServer() }.onAwait { it }
        async { getFromDB() }.onAwait { it }
    }.also {
        coroutineContext.cancelChildren()
    }
}

This would work?

[simon.vergauwen]

Arrow Fx offers some syntactic sugar on top of KotlinX.

[Pablo]

I'm not using Arrow Simon, otherwise I'd ask for Arrow stuff, I'm using Coroutines.

[simon.vergauwen]

The Github Arrow link I shared is the piece of code you're looking for. You can just copy-paste it.

[Francesc]

https://github.com/Kotlin/kotlinx.coroutines/issues/2867

[Nick Allen]

merge(::foo.asFlow(), ::bar.asFlow()).first()
If you have suspend methods foo and bar