OK, now this drives me nuts. Why doesn't it print ...

# coroutines

[azabost]

OK, now this drives me nuts. Why doesn't it print anything and deadlocks at flow.emit(1)?

fun main() = runBlocking {
    val flow = MutableSharedFlow<Int>()
    
    launch(<http://Dispatchers.IO|Dispatchers.IO>) {
        flow.onEach { println(it) }.first()
    }

    flow.emit(1)
}

[ephemient]

the launched coroutine is still running so the parent scope is kept alive

[azabost]

I know it's running, but why doesn't it print 1 ?

[ephemient]

the emit happens before the collector starts

[ephemient]

which means it's dropped

[azabost]

aaahhh

[ephemient]

launch(<http://Dispatchers.IO|Dispatchers.IO>, start = CoroutineStart.UNDISPATCHED) {
    flow.onEach { println(it) }.first()
}

will happen to wait for the collector to suspend before launch proceeds

[ephemient]

(has other potential side-effects so it's not always the right thing to do, but in this case…)

[azabost]

you are totally right

[azabost]

OMG, I guess it's getting too late

[azabost]

Thanks a lot 🍻