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https://issues.apache.org/jira/browse/ZOOKEEPER-2743?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15958322#comment-15958322
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ASF GitHub Bot commented on ZOOKEEPER-2743:
-------------------------------------------
Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/211#discussion_r110082136
--- Diff: src/java/main/org/apache/zookeeper/server/NettyServerCnxn.java ---
@@ -87,6 +87,12 @@ public void close() {
LOG.debug("close called for sessionid:0x"
+ Long.toHexString(sessionId));
}
+
+ // ZOOKEEPER-2743:
+ // Always unregister connection upon close to prevent
+ // connection bean leak under certain race conditions.
+ factory.unregisterConnection(this);
--- End diff --
Also it is guaranteed that the close call will be called at least once
after the cnx bean is registered (e.g. when sever shutdown, the factor will
iterate every cnx and close it..).
> Netty connection leaks JMX connection bean upon connection close in certain
> race conditions.
> --------------------------------------------------------------------------------------------
>
> Key: ZOOKEEPER-2743
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-2743
> Project: ZooKeeper
> Issue Type: Bug
> Components: server
> Affects Versions: 3.4.10, 3.5.2
> Reporter: Michael Han
> Assignee: Michael Han
> Labels: netty
>
> This is a tricky issue found while debugging failure of "flaky" watcher test
> (ZOOKEEPER-2686). When closing a Netty connection, depend on timing the
> connection bean registered when the connection was provisioned might not get
> unregistered, leading to leaked Java beans.
> The race happens at the time when the client is in the process of finalizing
> the session. As part of session finalization, a connection bean will be
> registered [1]. But right before the registering bean, the connection might
> gets closed, in cases for example the server that the client is connecting to
> is shutdown. As part of connection close, the bean will be un-registered, as
> expected [2], however the problem is when we execute at [2], the connection
> bean might not finish registering at [1], so the unregister of bean is a NOP.
> What's worse, as part of connection close, we remove this connection from
> connection factory [3], so future connection close call will get short
> circuited and directly return; in other words the bean unregister code in
> connection close call will only get executed once. Depends on luck, the bean
> might not get unregistered, as previously illustrated.
> [1]
> https://github.com/apache/zookeeper/blob/master/src/java/main/org/apache/zookeeper/server/ZooKeeperServer.java#L700
> [2]
> https://github.com/apache/zookeeper/blob/master/src/java/main/org/apache/zookeeper/server/NettyServerCnxn.java#L114
> [3]
> https://github.com/apache/zookeeper/blob/master/src/java/main/org/apache/zookeeper/server/NettyServerCnxn.java#L96
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