repeatWhenEmpty hangs on cancel when discard hook is present

[chringwer]

Expected Behavior

It should be safe to cancel the sequence.

Actual Behavior

Cancelling a sequence which is in a repeatWhenEmpty() loop will cause issues when a discard hook has been registered. In that case Operators.onDiscardMultiple() is invoked with the iterator used to keep track of the current iteration and the hook would be called for every remaining number up to Long.MAX_VALUE.

Steps to Reproduce

This test case will succeed when removing the doOnDiscard() operator.

@Test
public void shouldCompleteEventually()
{
    StepVerifier.create(Mono.empty()
                            .repeatWhenEmpty(Repeat.once())
                            .doOnDiscard(PooledDataBuffer.class, DataBufferUtils::release))
                .thenAwait()
                .thenCancel()
                .verify(Duration.ofSeconds(5));
}

Possible Solution

Probably we should treat the remaining iterations in a way that they can be safely discarded without bothering any application level hooks. Also, I guess FluxStream should not be considered "knownToBeFinite" if its size is Long.MAX_VALUE.

Your Environment

• Reactor version(s) used: 3.3.6.RELEASE

[simonbasle]

The operator is an alias, it could use .index() rather than a Stream for its purpose, which would eliminate the issue (see #2014 for context of the iteration)