println("before launch")
PlatformApiUtils.mainCoroutineScope.launch {
    println("before block")
    block()
    println("after block")
    isDoneAtomic.lazySet(true)
}
println("after launch")

println("before polling")
while(true) {
    ... poll for completion of '.launch { }'
}

class UI : CoroutineDispatcher() {
    override fun dispatch(context: CoroutineContext, block: Runnable) {
        val queue = dispatch_get_main_queue()
        dispatch_async(queue) {
            block.run()
        }
    }
}

before launch
after launch
before polling // I'd expect logging from inside the block after this line
polling timeout reached