code: public boolean addMessageListener(String topic, IKafkaMessageListener messageListener,
              boolean autoCommitOffsets) {
          synchronized (topicMsgListeners) {
              if (topicMsgListeners.put(topic, messageListener)) {
                  _getWorker(topic, autoCommitOffsets);
                  return true;
              }
          }
          return false;
      }
docs: Adds a message listener to a topic.
  
  @param topic
  @param messageListener
  @param autoCommitOffsets
  @return {@code true} if successful, {@code false} otherwise (the listener
  may have been added already)