@Override
  public void close() {
    if (closed.compareAndSet(false, true)) {
      LOG.debug("Close zookeeper connection {} to {}", getId(), connectString);
      tasks.add(CLOSE);
    }
  }
A very simple read only zookeeper implementation without watcher support.
hbase-client/src/main/java/org/apache/hadoop/hbase/zookeeper/ReadOnlyZKClient.java