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https://issues.apache.org/jira/browse/ZOOKEEPER-1683?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13628652#comment-13628652
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Shevek commented on ZOOKEEPER-1683:
-----------------------------------
volatile causes a write-read pair of the variable to form a transitive
happen-before relationship in the JMM. It does not solve the race - we (A)
could check sockKey != null, then the close() (B) could clear it, then we (A)
indirect on it, and we have an ABA race.
Personally, I would probably change testableCloseSocket to load sockKey into a
temporary local, then test for nullness of the local before indirecting on
that. No synchronization needed, and pointer assignment is always atomic, even
in 64-bit JVMs.
> 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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