[JENKINS-22932]

shutdownInput/Output is not idempotent, so attempting to reclose a closed socket fails.
[JENKINS-22932]

Don't let a failed SelectorTask kill the selector thread.
[FIXED JENKINS-22932]

If the thread that serves NioChannelHub.run() leaves for any reason, stop accepting the new connection as the channel will never be serviced.
It is indicative of a problem in the code.

This is the 3rd and the final part of the fix to the problem.