Is there any sane way to let ios implement a suspending interface? When we have an interface that s...

# multiplatform

[Paul Woitaschek]

Is there any sane way to let ios implement a suspending interface?

When we have an interface that suspends:

public fun runTest(suspending: SuspendingInterface) {
  CoroutineScope(Dispatchers.Default).launch {
    println(suspending.value())
  }
}

public interface SuspendingInterface {

  public suspend fun value(): Int
}

And ios switches threads:

class SuspendingInterfaceImpl : SuspendingInterface{
  func value(completionHandler: @escaping (KotlinInt?, Error?) -> Void) {
    DispatchQueue.global().async {
      completionHandler(42, nil)
    }
  }
}

CoroutineTest.runTest(SuspendingInterfaceImpl())

That directly fails with:

kotlin.native.IncorrectDereferenceException: illegal attempt to access non-shared kotlinx.coroutines.internal.DispatchedContinuation@1f67dc8 from other thread

[borisdamato]

Are you using the -native-mt version of coroutines? https://kotlinlang.org/docs/mobile/concurrency-and-coroutines.html#multithreaded-coroutines

[Paul Woitaschek]

Yep

[Johan Nenzén]

Reading this might get you in the right direction https://kotlinlang.org/docs/mobile/concurrency-overview.html#immutable-and-frozen-state

[Paul Woitaschek]

I don't think so

[Paul Woitaschek]

To me this pretty much looks like a bug

[Johan Nenzén]

Does it work if you wrap the entire call to 'value' in a dispatchqueue? Just making sure that the entire method is run on the same thread?

[Paul Woitaschek]

It's an example showing that suspend functions on iOS are heavily limited because you can't switch threads

[Johan Nenzén]

I won't argue with you about that. 😕