def deregister(io)
      @lock.synchronize do
        monitor = @selectables.delete IO.try_convert(io)
        monitor.close(false) if monitor && !monitor.closed?
        monitor
      end
    end
def deregister(io)
      @lock.synchronize do
        monitor = @selectables.delete IO.try_convert(io)
        monitor.close(false) if monitor && !monitor.closed?
        monitor
      end
    end
Deregister the given IO object from the selector