Concurrency and parallelism

You should use special approaches to deal with multithreading, such as RxJava or coroutines. Using RxJava, you can easily process asynchronous events in several threads:

fun singleBake(): Single<Cake> {
    return Single.fromCallable { bake() }.subscribeOn(Schedulers.computation())
}

fun reactiveOrder(amountOfCakes: Int): Single<List<Cake>> {
    val baker = Baker()
    return Observable.range(0, amountOfCakes)
            .flatMapSingle { baker.singleBake() }
            .toList()
}

.....................

Bakery().reactiveOrder(10)
 .subscribe { cakes -> println("Number of cakes: ${cakes.size}")}

Use common patterns to synchronize the work of several threads:

val lock = Lock()

Bakery().reactiveOrder(10)
        .doAfterTerminate { lock.unlock() }
        .subscribe { cakes ->  println("Number of cakes: ${cakes.size}")}

lock...