EmitterProcessor queue not cleared on immediate cancellation

[chringwer]

EmitterProcessor#remove has support to discard the buffer once the last subscriber is gone. However, it returns early if the subscribers array is already EMPTY. For cases where the subscription is immediately cancelled (e.g. .take(0)) this may leak the buffered elements.

Here is a repro case:

@Test
void shouldClearBufferOnCancellation() {
  BlockingQueue<Integer> queue = new LinkedBlockingQueue<>();

  Many<Integer> sink = Sinks.many().unicast().onBackpressureBuffer(queue);

  sink.tryEmitNext(1);
  sink.tryEmitNext(2);
  sink.tryEmitNext(3);

  assertThat(queue).hasSize(3);

  sink.asFlux().take(0).blockLast();

  assertThat(queue).isEmpty();
}

As a workaround .takeWhile(x -> false) does make the test pass for example.