8223353: (ch) Change channel close implementation to not wait for I/O threads

[Chris Hegarty]

> On 7 May 2019, at 14:58, Alan Bateman <Alan.Bateman at oracle.com> wrote:
> ... Part of the motivation now is Thread.interrupt to avoid that needing to wait. No change to non-blocking, the final close is always deferred when registered with one or more selectors.

Ok, this makes sense to me now. I didn't realize that in Java 11 a
thread interrupting another thread could potentially wait for I/O
operations to complete. It is certainly good to avoid this.

I wonder if a note should be added to the bug to capture this and the
little bit of history that has been discussed here, as it was not clear
to me.

BTW the changes look good.

-Chris.