Actually I guess that would be zookeeper.removeWatch( rootPath, tempWatcher
) !!
On Thu, Jun 11, 2009 at 10:14 AM, Satish Bhatti <cthd2...@gmail.com> wrote:
> That's right Ben. Basically, I would like to use it something like this:
> public boolean waitForChildrenChanged( String rootPath,
> long timeout )
> {
> BooleanLock blChildrenChanged = new BooleanLock();
>
> Watcher tempWatcher =
> new Watcher()
> {
> public void process( WatchedEvent event )
> {
> logger.debug( "waitForAnyEntry(): Got state event: " +
> ZooKeeperUtils.watchedEventToString( event ) );
> blChildrenChanged.setValue( true );
> }
> };
>
> zookeeper.getChildren( rootPath, watcher,
>
> new AsyncCallback.ChildrenCallback()
> {
> public void processResult( int rc, String path, Object ctx,
> List<String> children )
> {
> logger.debug( "waitForChildrenChanged():
> AsyncCallback.ChildrenCallback(): " + rc + ", " + path + ", " + ctx + ", " +
> children );
> }
> }, null );
>
> blChildrenChanged.waitUntilTrue( timeout );
>
> zookeeper.removeWatch( tempWatcher );
>
> return blChildrenChanged.isTrue();
> }
>
> The only piece missing from the API is the zookeeper.removeWatch(
> tempWatcher );
>
> Satish
>
>
> On Thu, Jun 11, 2009 at 7:09 AM, Benjamin Reed <br...@yahoo-inc.com>wrote:
>
>> just to clarify i believe you are talking about callbacks on the watch
>> object you are passing in the asynchronous call rather than the asynchronous
>> completion callback. (Henry is making the same assumption.) when you say you
>> are getting the callback 10 times, i believe your are talking about 10
>> different watch objects getting called back once each. right?
>>
>> it turns out that the zookeeper client does know what you are watching,
>> and the zookeeper server will only register one watch. the thing that is
>> missing is the clearWatches call that Henry refers to. the thing that
>> complicates things a bit, perhaps not for you, is the scenario where we have
>> different modules sharing the same zookeeper handle. if different modules
>> are interested in watching the same object, you don't want one module to
>> simply clear a the watches for a path because one module may mess up the
>> other.
>>
>> we have talked about adding this ability to clear watches for a while. i
>> think the auto-watch reregistration patch made the issue slightly more
>> pressing since it means that watches can survive for the entire lifetime of
>> a session not just for the duration of a connection to a specific server.
>> i've created ZOOKEEPER-442 to track this issue.
>>
>> ben
>>
>>
>> Henry Robinson wrote:
>>
>>> Hi Satish -
>>>
>>> As you've found out, you can set multiple identical watches per znode -
>>> the
>>> zookeeper client will not detect identical watches in case you really
>>> meant
>>> to call them several times. There's no way currently, as far as I know,
>>> to
>>> clear the watches once they've been set. So your options are either to
>>> avoid
>>> repeatedly setting them by detecting whether getChildren is a repeat
>>> call,
>>> or by dealing with multiple invocations on the callback path and not
>>> doing
>>> anything once you've established you're no longer interested.
>>>
>>> It might well make sense to add a clearWatches(path) call to the API,
>>> which
>>> would be useful particularly for clients where callbacks are expensive
>>> and
>>> require a context switch (which I think is true for all clients right
>>> now!).
>>>
>>> Henry
>>>
>>> On Wed, Jun 10, 2009 at 8:05 PM, Satish Bhatti <cthd2...@gmail.com>
>>> wrote:
>>>
>>>
>>>
>>>> I am using the asynchronous (callback) version of
>>>> zookeeper.getChildren().
>>>> That call returns immediately, I then wait for a certain time interval
>>>> for
>>>> nodes to appear, and if not I exit the method that made the
>>>> zookeeper.getChildren()
>>>> call. Later on, a node gets added under that node and I see in my
>>>> logfile
>>>> that the Watcher.process() callback that I set above gets called. Now
>>>> if I
>>>> make 10 failed attempts to get a node using the above technique, and at
>>>> some
>>>> later time a node does get added, I see in the logfile that the
>>>> Watcher.process() ends up being called 10 times! Of course by this time
>>>> I
>>>> have totally lost interest in those callbacks. Question: Is there a
>>>> way
>>>> to
>>>> remove that asynchronous callback? i.e. If I make a asynchronous
>>>> zookeeper.getChildren()
>>>> call, wait time t, give up, at that point can I remove the async
>>>> callback?
>>>> Satish
>>>>
>>>>
>>>>
>>>
>>
>
