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3.x: recursive concat causes StackOverflowError

See original GitHub issue

Originally posted on StackOverflow.

The following code crashes with StackOverflowError and the stacktrace shows a long chain of request calls.

import io.reactivex.rxjava3.core.Flowable
import io.reactivex.rxjava3.core.Single
import io.reactivex.rxjava3.schedulers.Schedulers
import java.util.concurrent.TimeUnit.SECONDS

fun main() {
    fun incr(n: Int): Single<Int> = Single.just(n + 1)

    fun numbers(n: Int, max: Int): Flowable<Int> = Flowable.just(n).concatWith(
        if (n < max)
            incr(n)
            .observeOn(Schedulers.single())
            .toFlowable()
            .concatMap { next -> numbers(next, max) }
        else
            Flowable.empty()
    )

    numbers(1, 10_000)
    .blockingForEach(::println)
}

Exception in thread "main" java.lang.StackOverflowError
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.operators.flowable.FlowableConcatMap$ConcatMapImmediate.request(FlowableConcatMap.java:215)
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.operators.flowable.FlowableConcatMap$ConcatMapImmediate.request(FlowableConcatMap.java:215)
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.subscriptions.SubscriptionArbiter.request(SubscriptionArbiter.java:135)
	at io.reactivex.rxjava3.internal.operators.flowable.FlowableConcatMap$ConcatMapImmediate.request(FlowableConcatMap.java:215)

I’m not sure why there is such a chain created and if this is a result of an RxJava bug or not.

Issue Analytics

State:
Created 3 years ago
Comments:5 (2 by maintainers)

Top GitHub Comments

1reaction

tmankitacommented, Jul 8, 2020

Hi, I would like to pick up this issue if no one is working on it yet.

0reactions

anastrcommented, Aug 12, 2020

it looks like each time you add new couple of concatWith-concatMap operators, so while the sequence grow up it must pass the emit to the whole concatWith-concatMap couples then to the Consumer. My only proof for that is that the last ‘1000’ emits will take longer time than first one.

I’m sorry to bother, but i have a question: in this case, why the error didn’t deliver to the consumer (onError has been implemented for sure)! if the max number was 1000, error will be thrown after complete!