I wonder why `generate` operator in the snippet be...

# rx

[dimsuz]

I wonder why generate operator in the snippet below causes tons of "received X" lines be printed between "fetched a page". Documentation suggests that emitter will be asked to emit by downstream and concatMap should ask for the next value upon completion of inner source (I guess). Any idea how can I make generate not eager in this scenario?

Observable
    .generate(
      { 0 },
      BiFunction { s: Int, emitter: Emitter<Int> -> emitter.onNext(s); s + 1 }
    )
    .doOnNext { println("received $it") }
    .concatMapSingle { page ->
      Single
        .just(if (page == 3) emptyList() else listOf(page))
        .delay(100, TimeUnit.MILLISECONDS)
    }
    .doOnNext { println("fetched a page") }
    .takeWhile { it.isNotEmpty() }
    .blockingSubscribe()