I was surprised to not get a response to this ... is this a no-brainer?
Too hard to solve? Did I not express it clearly? Am I doing something
dumb? :)
Thanks,
Eric
On 01/25/2010 01:05 PM, Eric Bowman wrote:
> I'm curious, what is the "best practice" for how to handle the case
> where re-adding a watch inside a Watcher.process callback fails?
>
> I keep stumbling upon the same kind of thing, and the possibility of
> race conditions or undefined behavior keep troubling me. Maybe I'm
> missing something.
>
> Suppose I have a callback like:
>
> public void process( WatchedEvent watchedEvent )
> {
> if ( watchedEvent.getType() ==
> Event.EventType.NodeChildrenChanged ) {
> try {
> ... do stuff ...
> }
> catch ( Throwable e ) {
> log.error( "Could not do stuff!", e );
> }
> try {
> zooKeeperManager.watchChildren( zPath, this );
> }
> catch ( InterruptedException e ) {
> log.info( "Interrupted adding watch -- shutting down?" );
> return;
> }
> catch ( KeeperException e ) {
> // oh crap, now what?
> }
> }
> }
>
> (In this cases, watchChildren is just calling getChildren and passing
> the watcher in.)
>
> It occurs to me I could get more and more complicated here: I could
> wrap watchChildren in a while loop until it succeeds, but that seems
> kind of rude to the caller. Plus what if I get a
> KeeperException.SessionExpiredException or a
> KeeperException.ConnectionLossException? How to handle that in this
> loop? Or I could send some other thread a message that it needs to keep
> trying until the watch has been re-added ... but ... yuck.
>
> I would very much like to just setup this watch once, and have ZooKeeper
> make sure it keeps firing until I tear down ZooKeeper -- this logic
> seems tricky for clients, and quite error prone and full of race conditions.
>
> Any thoughts?
>
> Thanks,
> Eric
>
>
--
Eric Bowman
Boboco Ltd
ebow...@boboco.ie
http://www.boboco.ie/ebowman/pubkey.pgp
+35318394189/+353872801532
