Any ideas why this prints: Inner Value: 0 Outer

fun main() {
   println("Outer")
   
   CoroutineScope(Dispatchers.Default).launch {
       getFlow()
            .onEach { println("Value: $it") }
            .collect()
   }
}


fun getFlow() = callbackFlow<Int> {
   println("Inner")
   delay(1)
   sendBlocking(0)
}

Shouldn't

Outer

get printed first?

If I run it as is then it simply prints

Outer

and exits. That’s correct. If I make

main

wait a little after launching the coroutine the program terminates with an error:

Outer
Inner
Value: 0
Exception in thread "DefaultDispatcher-worker-1" java.lang.IllegalStateException: 'awaitClose { yourCallbackOrListener.cancel() }' should be used in the end of callbackFlow block.
Otherwise, a callback/listener may leak in case of external cancellation.
See callbackFlow API documentation for the details.

That one just prints

Inner Outer

without anything else. Also correct. You run both in parallel so there’s no guarantee which one will happen first. Printing output isn’t always synchronous.

oh, ok. So its a race on

println

?

probably, yes

cool, thanks 👍