[JBoss JIRA] Created: (NETTY-256) A race condition during the recommended server shutdown procedure

[Trustin Lee (JIRA)]

A race condition during the recommended server shutdown procedure
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                 Key: NETTY-256
                 URL: https://jira.jboss.org/jira/browse/NETTY-256
             Project: Netty
          Issue Type: Bug
          Components: Transport
            Reporter: Trustin Lee
            Assignee: Trustin Lee
             Fix For: 3.2.0.ALPHA2


The recommended shutdown procedure, as documented, is:

1) Close the server socket (ServerSocketChannel.close().awaitUninterruptibly())
2) Close all open channels (preferably using ChannelGroup.close().awaitUninterruptibly())
3) Call ServerSocketChannelFactory.releaseExternalResources()

However, there is a race condition between the step 1 and 2:

[Boss thread] accepts a new connections from a client.
[User thread] ServerSocketChannel.close().awaitUninterruptibly() succeeds
[User thread] ChannelGroup.close() is called and all connections in the group are closed.
[Boss thread] triggers channelOpen/Bound/Connected event for the newly accepted channel
[Boss thread] the newly accepted channel is added to the ChannelGroup, but it's too late
[User thread] ServerSocketChannelFactory.releaseExternalResources() is called, but this is unexpected because there is still an active connection.

A workaround is to wait for the boss thread to be terminated or returned to the thread pool (e.g. wait for the termination of the boss thread between the step 1 and 2).  The proper fix is to make sure that the ChannelFuture returned by ServerSocketChannel.unbind/close() are notified *after* the boss thread is completely terminated.



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