Why does calling a launch within a launch throw an...

# kotlin-native

[Sam Schilling]

Why does calling a launch within a launch throw an IllegalStateException? I don’t want to have to wrap every launch call in runblocking whenever I want to do some background work, but is there another way around that?

// Fails
runBlocking {
    GlobalScope.launch {
        println(1)
        GlobalScope.launch { // IllegalStateException: no event loop, use runBlocking
            println(2)
        }
    }
}

// Succeeds
runBlocking {
    GlobalScope.launch {
        println(1)
        runBlocking {
            GlobalScope.launch {
                println(2)
            }
        }
    }
}

[Kris Wong]

event loops are thread-local

[Kris Wong]

definitely annoying

[Sam Schilling]

But what if I want to launch some async task without blocking execution? The runBlocking call blocks the calling thread until its coroutines, i.e., the nested launches, are complete.

[basher]

you can do a nested launch without GlobalScope

[Sam Schilling]

care to elaborate?

[basher]

oh actually nvm. i'm not actually sure how:

runBlocking {
    GlobalScope.launch {
    }
}

works since you're explicitly calling out to a scope that isn't the runBlocking . without understanding that, it's hard to elaborate my initial answer 🙂

[basher]

sorry