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https://issues.apache.org/jira/browse/ZOOKEEPER-1875?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17523057#comment-17523057
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Mohammad Arshad commented on ZOOKEEPER-1875:
--------------------------------------------
I have checked the zk client code carefully, NPE will occur only when watcher
is set null either throw ZooKeeper constructor or through register method. Now
I think we should do the exactly what had been submitted in latest
ZOOKEEPER-1875.patch.
> NullPointerException in ClientCnxn$EventThread.processEvent
> -----------------------------------------------------------
>
> Key: ZOOKEEPER-1875
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1875
> Project: ZooKeeper
> Issue Type: Bug
> Components: java client
> Affects Versions: 3.4.5, 3.4.10
> Reporter: Jerry He
> Assignee: Jerry He
> Priority: Minor
> Labels: pull-request-available
> Attachments: ZOOKEEPER-1875-trunk.patch, ZOOKEEPER-1875.patch,
> ZOOKEEPER-1875.patch
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> We've been seeing NullPointerException while working on HBase:
> {code}
> 14/01/30 22:15:25 INFO zookeeper.ZooKeeper: Client
> environment:user.dir=/home/biadmin/hbase-trunk
> 14/01/30 22:15:25 INFO zookeeper.ZooKeeper: Initiating client connection,
> connectString=hdtest009:2181 sessionTimeout=90000 watcher=null
> 14/01/30 22:15:25 INFO zookeeper.ClientCnxn: Opening socket connection to
> server hdtest009/9.30.194.18:2181. Will not attempt to authenticate using
> SASL (Unable to locate a login configuration)
> 14/01/30 22:15:25 INFO zookeeper.ClientCnxn: Socket connection established to
> hdtest009/9.30.194.18:2181, initiating session
> 14/01/30 22:15:25 INFO zookeeper.ClientCnxn: Session establishment complete
> on server hdtest009/9.30.194.18:2181, sessionid = 0x143986213e67e48,
> negotiated timeout = 60000
> 14/01/30 22:15:25 ERROR zookeeper.ClientCnxn: Error while calling watcher
> java.lang.NullPointerException
> at
> org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:519)
> at
> org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:495)
> {code}
> The reason is the watcher is null in this part of the code:
> {code}
> private void processEvent(Object event) {
> try {
> if (event instanceof WatcherSetEventPair) {
> // each watcher will process the event
> WatcherSetEventPair pair = (WatcherSetEventPair) event;
> for (Watcher watcher : pair.watchers) {
> try {
> watcher.process(pair.event);
> } catch (Throwable t) {
> LOG.error("Error while calling watcher ", t);
> }
> }
> {code}
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