Any ideas why this prints: Inner Value: 0 Outer ``...

# coroutines

[Shmuel Rosansky [G]]

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?

[Marc Knaup]

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.

[Marc Knaup]

(That’s on Kotlin/JVM)

[Shmuel Rosansky [G]]

https://pl.kotl.in/1MP3F9mAN

[Shmuel Rosansky [G]]

Thanks for the response @Marc Knaup!Maybe it's an issue with the playground?

[Marc Knaup]

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.

[Shmuel Rosansky [G]]

oh, ok. So its a race on println?

[Marc Knaup]

probably, yes

[Shmuel Rosansky [G]]

cool, thanks 👍