Neo,
To me it looks like this exception is while you are trying to call:
zk.create(path, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
where:
path = "/job_id/task_id/"
Does the node /job_id already exist when you are making this request?
Zookeeper does not recursively create the path you specify, only the
leaf node. If a parent in the path does not exist, you can get this
exception I believe.
As for your concern about the ordering of calling create and exist,
have you tried something like this:
if(zk.exists(path, watcher))
// start cleaning data in hdfs
If the watcher isn't going to get called (because the node already
exists), you can take action immediately rather than in the watcher
callback...
~Jared
On Sat, Nov 6, 2010 at 7:50 AM, Neo Anderson
<javadeveloper...@yahoo.co.uk> wrote:
> My question is - what is the right way to received notification once a znode
> is created?
>
> My scenario is that I have two threads, one (thread A) is going to save data
> to hdfs, another thread (thread B) is going to delete data stored in hdfs
> once thread A finishes its procedure. Thread A will create a znode and Thread
> B uses zk.exists() to register a watch.
>
> Thread A will only do
>
> zk.create(path, null, Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
>
> at the end (in the final block) of a clean function.
>
>
> The watcher in therad B
>
> Watcher watcher = new Watcher(){
> public void process(WatchedEvent e){
> boolean exist = e.getType().equals(EventType.NodeCreated);
> boolean path = e.getPath().equals("/"+job_id+"/"+task_id);
> if(exist && path){
> // start cleaning data in hdfs
> }
> }
>
> and
>
> pass watcher to zk.exists(path, watcher);
>
> but I gets `KeeperErrorCode = NoNode for' exception
>
> org.apache.zookeeper.KeeperException$NoNodeException: KeeperErrorCode =
> NoNode for /job_id/task_id
> at
> org.apache.zookeeper.KeeperException.create(KeeperException.java:102)
> at org.apache.zookeeper.KeeperException.create(KeeperException.java:42)
> at org.apache.zookeeper.ZooKeeper.create(ZooKeeper.java:637)
>
> It looks like znode doesn't exists because thread A still not yet create
> znode with path '/job_id/task_id'; however, if I switch to make thread A
> create znode first then therad B executes zk.exists(path, watcher). Problems
> becomes thread B (or its watcher) would never get triggered deleting data in
> hdfs.
>
> How to fix this?
>
> I appreciate any suggestion.
>
> Thanks.
>
>
>
>
>
>
>
>
