Rxjava: 2.x: Single, toObservable and share: sometimes NoSuchElementException

[neyron91]

Hello. I periodically have a NoSuchElementException. Version 2.1.12.

Code:

Single<String> single = Single.just("12345")
              .toObservable()
              .share()
              .singleOrError();

      for (int i = 0; i < 10; i++) {
         new Thread(() -> {
            single.subscribe((t) -> {
            }, thrw -> {
               if (NoSuchElementException.class.equals(thrw.getClass())) {
                  printStackTrace();
                  return;
               }
            });
         }).start();

         if (i % 2 != 0) {
            Thread.sleep(4);
         }
      }

Stacktrace:

at io.reactivex.internal.observers.ConsumerSingleObserver.onError(ConsumerSingleObserver.java:47)
    at io.reactivex.internal.operators.observable.ObservableSingleSingle$SingleElementObserver.onComplete(ObservableSingleSingle.java:113)
    at io.reactivex.internal.operators.observable.ObservableRefCount$ConnectionObserver.onComplete(ObservableRefCount.java:145)
    at io.reactivex.internal.operators.observable.ObservablePublish$PublishObserver.onComplete(ObservablePublish.java:193)
    at io.reactivex.internal.observers.DeferredScalarDisposable.complete(DeferredScalarDisposable.java:85)
    at io.reactivex.internal.operators.single.SingleToObservable$SingleToObservableObserver.onSuccess(SingleToObservable.java:73)
    at io.reactivex.internal.operators.single.SingleJust.subscribeActual(SingleJust.java:30)
    at io.reactivex.Single.subscribe(Single.java:3220)
    at io.reactivex.internal.operators.single.SingleToObservable.subscribeActual(SingleToObservable.java:36)
    at io.reactivex.Observable.subscribe(Observable.java:12005)
    at io.reactivex.internal.operators.observable.ObservablePublish.connect(ObservablePublish.java:116)
    at io.reactivex.internal.operators.observable.ObservableRefCount.subscribeActual(ObservableRefCount.java:68)
    at io.reactivex.Observable.subscribe(Observable.java:12005)
    at io.reactivex.internal.operators.observable.ObservableSingleSingle.subscribeActual(ObservableSingleSingle.java:35)
    at io.reactivex.Single.subscribe(Single.java:3220)
    at io.reactivex.Single.subscribe(Single.java:3206)

Is this a bug or an incorrect code? For cycle is written to demonstrate the problem.

[akarnokd]

This is a plausible outcome when using share. The underlying publish operator emits items to currently subscribed observers only. With that race in your code, some observers may come after the "12345" has been emitted but just before onComplete is signalled, thus they encounter an empty sequence.

Use replay(1).refCount() to ensure you don't lose that single item.

[neyron91]

Thanks, it works!