Hello! We have just upgraded kotlin and coroutines...

# coroutines

[Elisabet Svensson Duranovic]

Hello! We have just upgraded kotlin and coroutines for our service. One thing noted was that main can now be a suspend method. What happens if main gets suspended? Is there any considerations when having long-lived applications? (previously we did a runBlocking { application.start() }, now we just do application.start())

[marstran]

I'm pretty sure suspend fun main() { ... } is equivalent to fun main() = runBlocking { ... }.

[Elisabet Svensson Duranovic]

thanks! how sure is pretty sure?

[marstran]

I think I've read it somewhere. Trying to find it in the docs now 🙂

[marstran]

There's a paragraph about it here: https://blog.jetbrains.com/kotlin/2018/09/kotlin-1-3-rc-is-here-migrate-your-coroutines/

[Elisabet Svensson Duranovic]

awesome! thank you!

[Elisabet Svensson Duranovic]

Do I need to explicitly add the coroutineScope? In the example we have "suspend fun main() = coroutineScope { ... }" and I would have expected just "suspend fun main() { ... }"

[marstran]

You need that if you want to start other coroutines within main. Like the `async`s in that example.

[marstran]

So yeah, that is a difference. runBlocking would create that scope for you.

[Elisabet Svensson Duranovic]

I'm not sure I follow tbh. When would I/wouldn't I want that? What is the effect of either?

[marstran]

You need a coroutineScope to start coroutines like async, launch, produce and so on. It's part of something called "structured concurrency". You can read more about it here: https://medium.com/@elizarov/structured-concurrency-722d765aa952

[Elisabet Svensson Duranovic]

ahh - of course. async and the others start new coroutines - I was confused with just calling other suspend functions. Thanks for the link, will give it a read!

[marstran]

Right. You don't need a scope if you just want to call other suspend functions.