anything you use for a return path there will involve some overhead, but you can read the source for Channel, they're fairly small/don't involve a lot of initialization overhead. You might find

CompletableDeferred

to be a better option for just a single value though

How would I use it? Based on the little example I wrote (or something completely different)

probably something like

class Request<I, R>(val id: I) {
  val result: CompletableDeferred<R>()
}
val ch = Channel<Request<I, R>>()

with a send-request looking something like

val req = Request(id)
ch.send(req)
val result = req.result.await()

and then the receiver does

req.result.complete(fetchedValue)

Thanks a lot, I'll look into that ^^