@Override
    public int fill(Supplier<E> s)
    {
        return MessagePassingQueueUtil.fillBounded(this, s);
    }
{@inheritDoc}
<p>
Because return null indicates queue is empty we cannot simply rely on next element visibility for poll
and must test producer index when next element is not visible.
jctools-core/src/main/java/org/jctools/queues/MpmcArrayQueue.java