code: func (c *cacheWatcher) stop() {
  	c.Lock()
  	defer c.Unlock()
  	if !c.stopped {
  		c.stopped = true
  		close(c.done)
  		close(c.input)
  	}
  }
docs: // TODO(#73958)
  // stop() is protected by Cacher.Lock(), rename it to
  // stopThreadUnsafe and remove the sync.Mutex.