code: func (m *Broadcaster) stopWatching(id int64) {
  	m.lock.Lock()
  	defer m.lock.Unlock()
  	w, ok := m.watchers[id]
  	if !ok {
  		// No need to do anything, it's already been removed from the list.
  		return
  	}
  	delete(m.watchers, id)
  	close(w.result)
  }
docs: // stopWatching stops the given watcher and removes it from the list.