Interesting thing happened to me. I know its horri...

# compose-ios

[Joel Denke]

Interesting thing happened to me. I know its horrible code, but if using in a class member like:
val variable = runBlocking { listOf(fetchData) }
This works in Android but not in iOS, in iOS my entire screen was white without a trace saying why this happening. After a gazillion debug flows I randomly got a crash from coroutines in iOS threads handling.
Now I am curious, why does this happening? 😛

[Arkadii Ivanov]

You might be getting a deadlock on the main thread.

[Joel Denke]

Why is that happening on iOS but not Android? Absolutely this is very bad code like this. Just want to understand what the error was so I can avoid it in future.
I have some more runBlocking things and would like to be sure those do not causing this issue.
I think also its the combination of iOS viewcontroller root level injecting Koin component, that creating both the class mention above waiting but also waiting for the composable to be created at the same time, causing the deadlock. But still interesting.

[Arkadii Ivanov]

I might be wrong, but my understanding is that Android and iOS impls dispatch the continuation differently. I think Android impl schedules a job on background thread, then suspends, and then the continuation is called directly from the background thread. Whereas iOS dispatches from the background thread on main thread before calling the continuation, which is blocked.

[Joel Denke]

Does this also differs between desktop and web/wasm targets btw if you know? 🙂 Just trying to see how to avoid painpoints of differences in coroutines in KMP manner.

[Arkadii Ivanov]

I think it depends on what fetchData is.

[Arkadii Ivanov]

One pain point to avoid is runBlocking 🙂

[Joel Denke]

FetchData could be any async thing from server, database or such.

[Arkadii Ivanov]

Yeah, and the behaviour largely depends on that implementation. E.g. I think Ktor iOS dispatches responses on the main queue on iOS, so it should certainly cause a deadlock if the main thread is blocked.

[Joel Denke]

Right, yeah mixing stuff like androidx datastore, sqdelight, ktor and firestore 🙂 I guess importance of using correct withContext here from case to case.
However coroutines for iOS not supporting all dispatcher variants I think yet?

[Arkadii Ivanov]

iOS should now support all standard dispatchers, I believe.

[Joel Denke]

Oh from which kotlinx coroutine version if you know? 😮 Because I overload them now in Koin with "wrong" iOS implementation 😛

[Joel Denke]

Problably wrong doing this:

factory<CoroutineContext>(named(CoroutineDispatchersName.IoDispatcher)) { IosMainDispatcher }
    factory<CoroutineContext>(named(CoroutineDispatchersName.DefaultDispatcher)) { IosMainDispatcher }
    factory<CoroutineContext>(named(CoroutineDispatchersName.MainDispatcher)) { IosMainDispatcher }

object IosMainDispatcher : CoroutineDispatcher() {
    override fun dispatch(context: CoroutineContext, block: Runnable) {
        dispatch_async(dispatch_get_main_queue()) { block.run() }
    }
}

I couldnt find equivalent to Dispatchers.IO in Darwin. But bad documented, so I dont understand what I should be using.

[Arkadii Ivanov]

Yeah, looks like all your dispatchers are Main. You should be able to use Dispatchers.Main, Dispatchers.Default, Dispatchers,IO, etc.
IO is documented here: https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/-i-o.html

[Joel Denke]

Ah the Dispatchers.IO was an extension I had to import, which didnt exist in the past for me. Nice, finally I can use commonMain for coroutines for this and throw away my horrible shit solution run everything in main 😛 Thank you so much!

[Joel Denke]

The app went to be a lot more responsive in iOS now 😄 So huge success! Wow embarassing 😄