code: func (t *watcherBookmarkTimeBuckets) addWatcher(w *cacheWatcher) bool {
  	nextTime, ok := w.nextBookmarkTime(t.clock.Now())
  	if !ok {
  		return false
  	}
  	bucketID := nextTime.Unix()
  	if bucketID < t.startBucketID {
  		bucketID = t.startBucketID
  	}
  	watchers, _ := t.watchersBuckets[bucketID]
  	t.watchersBuckets[bucketID] = append(watchers, w)
  	return true
  }
docs: // adds a watcher to the bucket, if the deadline is before the start, it will be
  // added to the first one.