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From "Michael Han (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ZOOKEEPER-2743) Netty connection leaks JMX connection bean upon connection close in certain race conditions.
Date Sat, 01 Apr 2017 20:53:41 GMT

     [ https://issues.apache.org/jira/browse/ZOOKEEPER-2743?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael Han updated ZOOKEEPER-2743:
-----------------------------------
    Description: 
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

> 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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