code: func (l *State) NotifyProxy(ch chan<- struct{}) {
  	l.Lock()
  	defer l.Unlock()
  	l.managedProxyHandlers[ch] = struct{}{}
  }
docs: // NotifyProxy will register a channel to receive messages when the
  // configuration or set of proxies changes. This will not block on
  // channel send so ensure the channel has a buffer. Note that any buffer
  // size is generally fine since actual data is not sent over the channel,
  // so a dropped send due to a full buffer does not result in any loss of
  // data. The fact that a buffer already contains a notification means that
  // the receiver will still be notified that changes occurred.
  //
  // NOTE(mitchellh): This could be more generalized but for my use case I
  // only needed proxy events. In the future if it were to be generalized I
  // would add a new Notify method and remove the proxy-specific ones.