Rx2: Multiple errors in zip'ed observables throw exception

I execute multiple HTTP calls in parallel by zipping them up. Now 0…n of them can obviously fail. The thing is, when e.g. 2 calls fail at almost the exact time, error 1 is processed in doOnError and onErrorReturnItem but error 2 slips through and causes an exception. I think this happens if error 2 happens to come in while error 1 is still not processed entirely in those two onError operators.

It can be reproduced with the following simplified code:

buttonClick.flatMapSingle(action -> Single.zip(
                    Single.error(new Throwable("error 1")).delay(500, TimeUnit.MILLISECONDS),
                    Single.error(new Throwable("error 2")).delay(500, TimeUnit.MILLISECONDS),
                    (integer, integer2) -> true
            )
                    .doOnError(t -> Timber.d(t.getMessage()))
                    .onErrorReturnItem(true))
                    .subscribe();

So every once in a while this would throw:

D/Main: error 1
W/System.err: java.lang.Throwable: error 2

Shouldn’t the Single.zip stream only be allowed to emit one error?

[TillSimon]

It doesn’t seem to be happening with Observable.zip(), so I don’t know if that behavior makes sense…

[akarnokd]

I’m closing this issue due to inactivity. If you have further input on the issue, don’t hesitate to reopen this issue or post a new one.