Re: [Zookeeper-user] Leader election

[Avinash L. <avi...@gm...>]

Thanks for all suggestions. I have gotten it to work.

Avinash

On Mon, Jul 14, 2008 at 8:23 AM, Benjamin Reed <br...@ya...> wrote:

> The easiest way to fix this code is to move the Collections.sort(values) to
> right after the zk.getChildren() and then use the following Comparator with
> Collections.sort() and Collections.binarySearch():
>
> /* This Comparator defines an ordering such that the strings with
>  * the lowest sequence numbers are first in sequence sorted order
>  * followed by strings without sequence numbers in lexographical
>  * order. This class assumes that a '-' preceeds the sequence
>  * number. */
> class SequenceComparator implements Comparator<String> {
>
>    @Override
>    public int compare(String o1, String o2) {
>        int s1 = getSequence(o1);
>        int s2 = getSequence(o2);
>        if (s1 == -1 && s2 == -1) {
>            return o1.compareTo(o2);
>        }
>        return s1 == -1 ? 1 : s2 == -1 ? -1 : s1 - s2 ? : -1;
>    }
>
>    /* Returns the sequence suffix of s. This method assumes that
>     * the sequence number is prefixed with a '-'. */
>    private int getSequence(String s) {
>        int i = s.lastIndexOf('-');
>        if (i != -1) {
>            try {
>                return Integer.parseInt(s.substring(i+1));
>            // If an exception occurred we misdetected a sequence suffix,
>            // so return -1.
>            } catch(NumberFormatException e) {
>            } catch(ArrayIndexOutOfBoundsException e) {
>            }
>        }
>        return -1;
>    }
> }
>
> ben
>
> On Thursday 10 July 2008 22:20:06 Avinash Lakshman wrote:
> > Hi
> >
> > I am trying to elect leader among 50 nodes. There is always one odd guy
> who
> > seems to think that someone else distinct from what some other nodes see
> as
> > leader. Could someone please tell me what is wrong with the following
> code
> > for leader election:
> >
> > public void electLeader()
> >         {
> >             ZooKeeper zk =
> StorageService.instance().getZooKeeperHandle();
> >             String path = "/Leader";
> >             try
> >             {
> >                 String createPath = path +
> > "/L-";
> >                 LeaderElector.createLock_.lock();
> >                 while( true )
> >                 {
> >                     /* Get all znodes under the Leader znode */
> >                     List<String> values = zk.getChildren(path, false);
> >                     /*
> >                      * Get the first znode and if it is the
> >                      * pathCreated created above then the data
> >                      * in that znode is the leader's identity.
> >                     */
> >                     if ( leader_ == null )
> >                     {
> >                         leader_ = new AtomicReference<EndPoint>(
> > EndPoint.fromBytes( zk.getData(path + "/" + values.get(0), false, null) )
> > ); }
> >                     else
> >                     {
> >                         leader_.set( EndPoint.fromBytes( zk.getData(path
> +
> > "/" + values .get(0), false, null) ) );
> >                         /* Disseminate the state as to who the leader is.
> > */ onLeaderElection();
> >                     }
> >                     logger_.debug("Elected leader is " + leader_ + " @
> > znode " + ( path + "/" + values.get(0) ) );
> >                     Collections.sort(values);
> >                     /* We need only the last portion of this znode */
> >                     String[] peices = pathCreated_.split("/");
> >                     int index = Collections.binarySearch(values,
> > peices[peices.length - 1]);
> >                     if ( index > 0 )
> >                     {
> >                         String pathToCheck = path + "/" +
> values.get(index
> > - 1);
> >                         Stat stat = zk.exists(pathToCheck, true);
> >                         if ( stat != null )
> >                         {
> >                             logger_.debug("Awaiting my turn ...");
> >                             condition_.await();
> >                             logger_.debug("Checking to see if leader is
> > around ...");
> >                         }
> >                     }
> >                     else
> >                     {
> >                         break;
> >                     }
> >                 }
> >             }
> >             catch ( InterruptedException ex )
> >             {
> >                 logger_.warn(LogUtil.throwableToString(ex));
> >             }
> >             catch ( KeeperException ex )
> >             {
> >                 logger_.warn(LogUtil.throwableToString(ex));
> >             }
> >             finally
> >             {
> >                 LeaderElector.createLock_.unlock();
> >             }
> >         }
> >     }
> >
> > Thanks
> > Avinash
>
>
>