private val uploadSchedules = Schedulers.from(Executors.newFixedThreadPool(5))

fun upload(request: Request) : Completable {
      Observable.just(request)
         .flatMap { request -> upload(request).subscribeOn(uploadScheduler) }
}

fun upload(requests: List<Request>) : Completable {
      Observable.fromIterable(requests)
		 // here the subscriptions order are race-y, I want to want them ordered by the order of the list--|
         .flatMap { request -> upload(request)															   |
						.subscribeOn(uploadScheduler)													   |
						.doOnSubscribe { log(request) }  <-------------------------------------------------|
		 }
}

// log outputs:
// request 0
// request 3
// request 4
// request 2
// request 1
// etc, race-y, random order