class NIO::Selector

def wakeup

level-triggered behavior.
has the same effect as invoking it just once. In other words, it provides
Invoking this method more than once between two successive select calls

any such thread exists.
Wake up a thread that's in the middle of selecting on this selector, if
def wakeup
  # Send the selector a signal in the form of writing data to a pipe
  @waker.write "\0"
  nil
end