Hey there! So a colleague tried out the ktor call ...

# kotlin-native

[Marc Reichelt]

Hey there! So a colleague tried out the ktor call I implemented in the SharedCode framework, but he got a crash with EXC_BAD_ACCESS. So what happened here? It looks like a bug in coroutines, but I don’t know.
How do we debug crashes like this, and most importantly: how do we fix it?

[kpgalligan]

message has been deleted

[kpgalligan]

Coroutines in native can’t be used between multiple threads. You can use Ktor to make network calls, but you have to be careful in some cases. What does the code look like?

[Marc Reichelt]

It’s basically a runBlocking around a ktor call

[Marc Reichelt]

and the whole thing is called from a background thread

[Marc Reichelt]

This is our approach, while runBlocking is an expect fun that uses the actual native implementation of the same name

Untitled

[Marc Reichelt]

so what’s a good pattern?

[Marc Reichelt]

and still, it would be nice to know how to debug these forms of crashes…

[kpgalligan]

On my phone now so hard to comment

[kpgalligan]

Debugging that one would be tough. The native Ktor client for iOS expects to return to the main thread. I would assume that's ultimately what's causing that issue. Seeing the source code for that if tricky because of how the compiler embeds file info (I assume). For your code you'd have the source open

[kpgalligan]

I think there's a need for a sync mode network library. Ktor kind of expects to suspend

[Marc Reichelt]

Hmm, so call it from the main thread then I guess

[kpgalligan]

More source context might help. Also wondering if any log info printed below?

[Marc Reichelt]

can the shared code then simply expose suspend functions?

[Marc Reichelt]

on https://kotlinlang.org/docs/reference/native/objc_interop.html it says they are ‘unsupported’

[kpgalligan]

No. To get back to ios you'd need see form of callback. I use Swift lambdas, generally

[kpgalligan]

This is where an alternate networking lib would be good. If you want to manage concurrency in iOS rather than kotlin (which many teams do)

[Marc Reichelt]

but to get around the limitation of not having suspend functions here, I assume I will have to use runBlocking anyway

[kpgalligan]

No. Take a callback lambda, launch coroutine in kotlin. The call will return to ios, suspend in kotlin. When resumed, the lambda is called in main thread

[Marc Reichelt]

that sounds like the way to go

[Marc Reichelt]

any good example code on this one?

[kpgalligan]

Not exactly. Here's some but there are multiple layers to dig through https://github.com/touchlab/DroidconKotlin/blob/master/sessionize/lib/src/iosMain/kotlin/co/touchlab/sessionize/SpeakerViewModel.kt#L5

[kpgalligan]

Again, on phone. Nav is hard

[Marc Reichelt]

no problem - I’ll check back tomorrow 🙂

[Marc Reichelt]

thanks for all the help, I really appreciate it!

[Marc Reichelt]

I found https://www.kotlindevelopment.com/kotlin-multiplatform-in-action/, that looks like what you meant

[Marc Reichelt]

yep: https://github.com/adrianbukros/github-multiplatform-example/blob/master/shared/src/commonMain/kotlin/com/adrianbukros/github/example/Api.kt#L28-L49