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From "Jerry He (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-11018) ZKUtil.getChildDataAndWatchForNewChildren() will not return null as indicated
Date Thu, 17 Apr 2014 20:39:21 GMT
Jerry He created HBASE-11018:

             Summary: ZKUtil.getChildDataAndWatchForNewChildren() will not return null as
                 Key: HBASE-11018
                 URL: https://issues.apache.org/jira/browse/HBASE-11018
             Project: HBase
          Issue Type: Bug
          Components: Zookeeper
    Affects Versions: 0.98.1, 0.96.1
            Reporter: Jerry He
            Assignee: Jerry He
            Priority: Minor

While working on HBase acl, I found out that ZKUtil.getChildDataAndWatchForNewChildren() will
not return null as indicated.  Here is the code:
   * Returns null if the specified node does not exist.  Otherwise returns a
   * list of children of the specified node.  If the node exists but it has no
   * children, an empty list will be returned.
  public static List<NodeAndData> getChildDataAndWatchForNewChildren(
      ZooKeeperWatcher zkw, String baseNode) throws KeeperException {
    List<String> nodes =
      ZKUtil.listChildrenAndWatchForNewChildren(zkw, baseNode);
    List<NodeAndData> newNodes = new ArrayList<NodeAndData>();
    if (nodes != null) {
      for (String node : nodes) {
        String nodePath = ZKUtil.joinZNode(baseNode, node);
        byte[] data = ZKUtil.getDataAndWatch(zkw, nodePath);
        newNodes.add(new NodeAndData(nodePath, data));
    return newNodes;
We return 'newNodes' which will never be null.

This is a deprecated method.  But it is still used in HBase code.
For example: org.apache.hadoop.hbase.security.access.ZKPermissionWatcher.start()
  public void start() throws KeeperException {
    if (ZKUtil.watchAndCheckExists(watcher, aclZNode)) {
      List<ZKUtil.NodeAndData> existing =
          ZKUtil.getChildDataAndWatchForNewChildren(watcher, aclZNode);
      if (existing != null) {
We test the 'null' return from the call which becomes the problem.

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