code: def link(self, pid, to):
      
  
      self._assert_started()
  
      def really_link():
        self._links[pid].add(to)
        log.info('Added link from %s to %s' % (pid, to))
  
      def on_connect(stream):
        really_link()
  
      if self._is_local(pid):
        really_link()
      else:
        self.__loop.add_callback(self._maybe_connect, to, on_connect)
docs: Link a local process to a possibly remote process.
  
      Note: It is more idiomatic to call ``link`` directly on the bound Process
      object instead.
  
      When ``pid`` is linked to ``to``, the termination of the ``to`` process
      (or the severing of its connection from the Process ``pid``) will result
      in the local process' ``exited`` method to be called with ``to``.
  
      This method returns immediately.
  
      :param pid: The pid of the linking process.
      :type pid: :class:`PID`
      :param to: The pid of the linked process.
      :type to: :class:`PID`
      :returns: Nothing