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From Todd Nine <t...@spidertracks.co.nz>
Subject Re: Receiving create events for self with synchronous create
Date Fri, 27 Aug 2010 03:09:53 GMT
Sure thing.  The FollowerWatcher class is instantiated by the
IClusterManager implementation.    It then performs the following

FollowerWatcher.init() which is intended to do the following.

1. Create our follower node so that other nodes know we exist at path
"/com/spidertracks/aviator/cluster/follower/"  where the last
node is an ephemeral node with the internal IP address of the node.
These are lines 67 through 72.
2. Signal to the clusterManager that the cluster has changed (line 79).
Ultimately the clusterManager will perform a barrier for partitioning
data ( a separate watcher)
3. Register a watcher to receive all future events on the follower path
"/com/spidertracks/aviator/cluster/follower/" line 81.

Then we have the following characteristics in the watcher

1. If a node has been added or deleted from the children of
"/com/spidertracks/aviator/cluster/follower" then continue.  Otherwise,
ignore the event.  Lines 33 through 44
2. If this was an event we should process our cluster has changed,
signal to the CusterManager that a node has either been added or
removed. line 51.

I'm trying to encapsulate the detection of additions and deletions of
child nodes within this Watcher.  All other events that occur due to a
node being added or deleted should be handled externally by the


On Thu, 2010-08-26 at 19:26 -0700, Mahadev Konar wrote:

> Hi Todd,
>   The code that you point to, I am not able to make out the sequence
> of steps.
>    Can you be more clear on what you are trying to do in terms of
> zookeeper api?
> Thanks
> mahadev
> On 8/26/10 5:58 PM, "Todd Nine" <todd@spidertracks.co.nz> wrote:
>         Hi all,
>           I'm running into a strange issue I could use a hand with.
>           I've
>         implemented leader election, and this is working well.  I'm
>         now
>         implementing a follower queue with ephemeral nodes. I have an
>         interface
>         IClusterManager which simply has the api "clusterChanged".  I
>         don't care
>         if nodes are added or deleted, I always want to fire this
>         event.  I have
>         the following basic algorithm.
>         init
>         Create a path with "/follower/"+mynode name
>         fire the clusterChangedEvent
>         Watch set the event watcher on the path "/follower".
>         watch:
>         reset the watch on "/follower"
>         if event is not a NodeDeleted or NodeCreated, ignore
>         fire the clustermanager event
>         this seems pretty straightforward.  Here is what I'm expecting
>         1. Create my node path
>         2. fire the clusterChanged event
>         3. Set watch on "/follower"
>         4. Receive watch events for changes from any other nodes.
>         What's actually happening
>         1. Create my node path
>         2. fire the clusterChanged event
>         3. Set Watch on "/follower"
>         4. Receive watch event for node created in step 1
>         5. Receive future watch events for changes from any other
>         nodes.
>         Here is my code.  Since I set the watch after I create the
>         node, I'm not
>         expecting to receive the event for it.  Am I doing something
>         incorrectly
>         in creating my watch?  Here is my code.
>         http://pastebin.com/zDXgLagd
>         Thanks,
>         Todd

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