Closes this selectable channel.
This method is invoked by the
close method in order to perform the actual work of closing the
channel. This method is only invoked if the channel has not yet been
closed, and it is never invoked more than once.
An implementation of this method must arrange for any other thread that is blocked in an I/O operation upon this channel to return immediately, either by throwing an exception or by returning normally.
|If an I/O error occurs|