Element ordering in Rx operators

Main.kt

import io.reactivex.Observable
import io.reactivex.schedulers.Schedulers
import java.util.concurrent.TimeUnit
import kotlin.random.Random

fun main() {
    /*
     * Output:
     *
     * 0
     * 1
     * 2
     * 3
     * 4
     */
    println("map")
    Observable.interval(100, TimeUnit.MILLISECONDS)
        .take(5)
        .map {
            Thread.sleep(Random.nextLong(1000))
            it.toString()
        }
        .subscribeOn(Schedulers.io())
        .doOnNext(::println)
        .blockingSubscribe()

    /*
     * Sample output:
     *
     * 2a
     * 3a
     * 1a
     * 3b
     * 0a
     * 4a
     * 1b
     * 2b
     * 4b
     * 0b
     */
    println("flatMap")
    Observable.interval(100, TimeUnit.MILLISECONDS)
        .take(5)
        .flatMap { value ->
            Observable.fromArray("a", "b")
                .map {
                    Thread.sleep(Random.nextLong(1000))
                    "$value$it"
                }
                .subscribeOn(Schedulers.io())
        }
        .subscribeOn(Schedulers.io())
        .doOnNext(::println)
        .blockingSubscribe()

    /*
     * Output:
     *
     * 0a
     * 0b
     * 1a
     * 1b
     * 2a
     * 2b
     * 3a
     * 3b
     * 4a
     * 4b
     */
    println("concatMap")
    Observable.interval(100, TimeUnit.MILLISECONDS)
        .take(5)
        .concatMap { value ->
            Observable.fromArray("a", "b")
                .map {
                    Thread.sleep(Random.nextLong(1000))
                    "$value$it"
                }
                .subscribeOn(Schedulers.io())
        }
        .subscribeOn(Schedulers.io())
        .doOnNext(::println)
        .blockingSubscribe()

    /*
     * Sample output:
     *
     * Skipped 0a
     * Skipped 1a
     * 2a
     * Skipped 2b
     * 3a
     * 3b
     * 4a
     * 4b
     */
    println("switchMap")
    Observable.interval(100, TimeUnit.MILLISECONDS)
        .take(5)
        .switchMap { value ->
            Observable.fromArray("a", "b")
                .map {
                    try {
                        Thread.sleep(Random.nextLong(200))
                    } catch (e: Exception) {
                        println("Skipped $value$it")
                        Thread.currentThread().interrupt()
                    }
                    "$value$it"
                }
                .subscribeOn(Schedulers.io())
        }
        .subscribeOn(Schedulers.io())
        .doOnNext(::println)
        .blockingSubscribe()
}