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https://issues.apache.org/jira/browse/ZOOKEEPER-1731?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13727807#comment-13727807
]
Camille Fournier commented on ZOOKEEPER-1731:
---------------------------------------------
Looks good checking in
> Unsynchronized access to ServerCnxnFactory.connectionBeans results in deadlock
> ------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-1731
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1731
> Project: ZooKeeper
> Issue Type: Bug
> Reporter: Dave Latham
> Priority: Critical
> Fix For: 3.4.6
>
> Attachments: ZOOKEEPER-1731.patch
>
>
> We had a cluster of 3 peers (running 3.4.3) fail after we took down 1 peer
> briefly for maintenance. A second peer became unresponsive and the leader
> lost quorum. Thread dumps on the second peer showed two threads consistently
> stuck in these states:
> {noformat}
> "QuorumPeer[myid=0]/0.0.0.0:2181" prio=10 tid=0x00002aaab8d20800 nid=0x598a
> runnable [0x000000004335d000]
> java.lang.Thread.State: RUNNABLE
> at java.util.HashMap.put(HashMap.java:405)
> at
> org.apache.zookeeper.server.ServerCnxnFactory.registerConnection(ServerCnxnFactory.java:131)
> at
> org.apache.zookeeper.server.ZooKeeperServer.finishSessionInit(ZooKeeperServer.java:572)
> at
> org.apache.zookeeper.server.quorum.Learner.revalidate(Learner.java:444)
> at
> org.apache.zookeeper.server.quorum.Follower.processPacket(Follower.java:133)
> at
> org.apache.zookeeper.server.quorum.Follower.followLeader(Follower.java:86)
> at
> org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:740)
> "NIOServerCxn.Factory:0.0.0.0/0.0.0.0:2181" daemon prio=10
> tid=0x00002aaab84b0800 nid=0x5986 runnable [0x0000000040878000]
> java.lang.Thread.State: RUNNABLE
> at java.util.HashMap.removeEntryForKey(HashMap.java:614)
> at java.util.HashMap.remove(HashMap.java:581)
> at
> org.apache.zookeeper.server.ServerCnxnFactory.unregisterConnection(ServerCnxnFactory.java:120)
> at
> org.apache.zookeeper.server.NIOServerCnxn.close(NIOServerCnxn.java:971)
> - locked <0x000000078d8a51f0> (a java.util.HashSet)
> at
> org.apache.zookeeper.server.NIOServerCnxnFactory.closeSessionWithoutWakeup(NIOServerCnxnFactory.java:307)
> at
> org.apache.zookeeper.server.NIOServerCnxnFactory.closeSession(NIOServerCnxnFactory.java:294)
> - locked <0x000000078d82c750> (a
> org.apache.zookeeper.server.NIOServerCnxnFactory)
> at
> org.apache.zookeeper.server.ZooKeeperServer.processConnectRequest(ZooKeeperServer.java:834)
> at
> org.apache.zookeeper.server.NIOServerCnxn.readConnectRequest(NIOServerCnxn.java:410)
> at
> org.apache.zookeeper.server.NIOServerCnxn.readPayload(NIOServerCnxn.java:200)
> at
> org.apache.zookeeper.server.NIOServerCnxn.doIO(NIOServerCnxn.java:236)
> at
> org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:224)
> at java.lang.Thread.run(Thread.java:662)
> {noformat}
> It shows both threads concurrently modifying
> ServerCnxnFactory.connectionBeans which is a java.util.HashMap.
> This cluster was serving thousands of clients, which seems to make this
> condition more likely as it appears to occur when one client connects and
> another disconnects at about the same time.
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