code: func (c *cache) UpdateTime(timestamp time.Time) {
  	c.lock.Lock()
  	defer c.lock.Unlock()
  	c.timestamp = &timestamp
  	// Notify all the subscribers if the condition is met.
  	for id := range c.subscribers {
  		c.notify(id, *c.timestamp)
  	}
  }
docs: //  UpdateTime modifies the global timestamp of the cache and notify
  //  subscribers if needed.