docs: public void ack(long hsId, boolean isEOS, long targetId, int blockIndex) {
          rejoinLog.debug("Queue ack for hsId:" + hsId + " isEOS: " +
                  isEOS + " targetId:" + targetId + " blockIndex: " + blockIndex);
          m_blockIndices.offer(Pair.of(hsId, new RejoinDataAckMessage(isEOS, targetId, blockIndex)));
      }