Closes this channel.
After a channel is closed, any further attempt to invoke I/O
operations upon it will cause a
ClosedChannelException to be
If this channel is already closed then invoking this method has no effect.
This method may be invoked at any time. If some other thread has already invoked it, however, then another invocation will block until the first invocation is complete, after which it will return without effect.
|If an I/O error occurs|