I have a node that has a children watch on it. Whenever the
NodeChildrenChanged event is received I obtain the children using
getChildren passing in my watcher then iterate through all children
and perform a getData() also passing in my watcher so that I am also
notified of any changes to the data on the children.
E.g.
public void check() {
List<String> children =
zkclient.getChildren().usingWatcher(myWatcher).forPath(PATH);
for (String name : children) {
byte[] data =
zkclient.getData().usingWatcher(myWatcher).forPath(getPathFromName(name));
// do stuff
}
}
CuratorWatcher myWatcher = new CuratorWatcher() {
@Override
public void process(WatchedEvent event) throws Exception {
logger.info("received watch event: " + event);
if (event.getType().equals(EventType.NodeChildrenChanged)
|| event.getType().equals(EventType.NodeDataChanged)) {
check();
}
}
};
This means that whenever a child is added/removed, another getData
call will be made with the watcher.
After reading the ZooKeeper documentation I thought it would be fine
to keep setting the watcher since I should only be given the same
watch notification once:
“A watch object, or function/context pair, will only be triggered once
for a given notification. For example, if the same watch object is
registered for an exists and a getData call for the same file and that
file is then deleted, the watch object would only be invoked once with
the deletion notification for the file.”
http://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html#ch_zkWatches
However I have observed that when a node is deleted I am receiving the
NodeDeleted watch event multiple times:
received watch event: WatchedEvent state:SyncConnected
type:NodeDeleted path:/a/b
received watch event: WatchedEvent state:SyncConnected
type:NodeDeleted path:/a/b
received watch event: WatchedEvent state:SyncConnected
type:NodeDeleted path:/a/b
...
This means the watch is being triggered multiple times unnecessarily.
I am using the Curator framework however I believe this just passes
the watches through and therefore this is a ZooKeeper issue. I am
using zookeeper server version 3.4.5, zookeeper client 3.3.1,
curator-framework 1.2.2.
Is the documentation wrong / is this a bug or have I misunderstood?
Many thanks,
Jon
