code: def close(self):
          
          with self._close_lock:
              epfd = self._epfd
              if epfd >= 0:
                  self._epfd = -1
                  close(epfd)
docs: Close the internal epoll file descriptor if it isn't closed
  
          :raises OSError:
              If the underlying ``close(2)`` fails. The error message matches
              those found in the manual page.