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https://issues.apache.org/jira/browse/KAFKA-16765?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17846475#comment-17846475
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Greg Harris commented on KAFKA-16765:
-------------------------------------
This is also a bug in EchoServer:
[https://github.com/apache/kafka/blob/cb968845ecb3cb0982182d9dd437ecf652fe38d3/clients/src/test/java/org/apache/kafka/common/network/EchoServer.java#L76-L81]
and ServerShutdownTest:
[https://github.com/apache/kafka/blob/cb968845ecb3cb0982182d9dd437ecf652fe38d3/core/src/test/scala/unit/kafka/server/ServerShutdownTest.scala#L274-L275]
except those don't require a race condition to happen.
> NioEchoServer leaks accepted SocketChannel instances due to race condition
> --------------------------------------------------------------------------
>
> Key: KAFKA-16765
> URL: https://issues.apache.org/jira/browse/KAFKA-16765
> Project: Kafka
> Issue Type: Bug
> Components: core, unit tests
> Affects Versions: 3.8.0
> Reporter: Greg Harris
> Priority: Minor
>
> The NioEchoServer has an AcceptorThread that calls accept() to open new
> SocketChannel instances and insert them into the `newChannels` List, and a
> main thread that drains the `newChannels` List and moves them to the
> `socketChannels` List.
> During shutdown, the serverSocketChannel is closed, which causes both threads
> to exit their while loops. It is possible for the NioEchoServer main thread
> to sense the serverSocketChannel close and terminate before the Acceptor
> thread does, and for the Acceptor thread to put a SocketChannel in
> `newChannels` before terminating. This instance is never closed by either
> thread, because it is never moved to `socketChannels`.
> A precise execution order that has this leak is:
> 1. NioEchoServer thread locks `newChannels`.
> 2. Acceptor thread accept() completes, and the SocketChannel is created
> 3. Acceptor thread blocks waiting for the `newChannels` lock
> 4. NioEchoServer thread releases the `newChannels` lock and does some
> processing
> 5. NioEchoServer#close() is called, which closes the serverSocketChannel
> 6. NioEchoServer thread checks serverSocketChannel.isOpen() and then
> terminates
> 7. Acceptor thread acquires the `newChannels` lock and adds the SocketChannel
> to `newChannels`.
> 8. Acceptor thread checks serverSocketChannel.isOpen() and then terminates.
> 9. NioEchoServer#close() stops blocking now that both other threads have
> terminated.
> The end result is that the leaked socket is left open in the `newChannels`
> list at the end of close(), which is incorrect.
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