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https://issues.apache.org/jira/browse/ZOOKEEPER-1683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13628622#comment-13628622
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Shevek commented on ZOOKEEPER-1683:
-----------------------------------
I think you can't just check isConnected() / sockKey != null because it's being
set to null on a different thread, so then there will be a race for the NPE
instead of just an NPE.
One of the other issues with this thread contract, where values are set within
an object which is accessible to more than one thread is that JSR133 says that
assignments performed in constructors do not happen-before the constructor
returns unless the variable being assigned is final. Since ClientCnxnNIO is
accessible to more than one thread at the point variables like sockKey are
initialized, I suspect the code violates the JMM anyway.
A much better solution would be to use more immutable variables, and discard
and reconstruct objects rather than attempting to modify them. An ideal
solution would be to use something like netty, which is designed to handle and
abstract all these cases.
> ZooKeeper client NPE when updating server list on disconnected client
> ---------------------------------------------------------------------
>
> Key: ZOOKEEPER-1683
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1683
> Project: ZooKeeper
> Issue Type: Bug
> Components: java client
> Affects Versions: 3.5.0
> Reporter: Shevek
> Assignee: Alexander Shraer
> Fix For: 3.5.0
>
> Attachments: ZOOKEEPER-1683.patch, ZOOKEEPER-1683-ver1.patch
>
>
> 2013-04-04 22:16:15,872 ERROR [pool-4-thread-1]
> com.netflix.curator.ConnectionState.getZooKeeper (ConnectionState.java:84) -
> Background exception caught
> java.lang.NullPointerException
> at
> org.apache.zookeeper.client.StaticHostProvider.updateServerList(StaticHostProvider.java:161)
> ~[zookeeper-3.5.0.jar:3.5.0--1]
> at
> org.apache.zookeeper.ZooKeeper.updateServerList(ZooKeeper.java:183)
> ~[zookeeper-3.5.0.jar:3.5.0--1]
> at
> com.netflix.curator.HandleHolder$1$1.setConnectionString(HandleHolder.java:121)
> ~[curator-client-1.3.5-SNAPSHOT.jar:?]
> The duff code is this:
> ClientCnxnSocket clientCnxnSocket = cnxn.sendThread.getClientCnxnSocket();
> InetSocketAddress currentHost = (InetSocketAddress)
> clientCnxnSocket.getRemoteSocketAddress();
> boolean reconfigMode = hostProvider.updateServerList(serverAddresses,
> currentHost);
> Now, currentHost might be null, if we're not yet connected. But
> StaticHostProvider.updateServerList indirects on it unconditionally.
> This would be caught by findbugs.
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