code: func (s *Simulation) UpNodesItems(key interface{}) (values map[enode.ID]interface{}) {
  	s.mu.RLock()
  	defer s.mu.RUnlock()
  
  	ids := s.UpNodeIDs()
  	values = make(map[enode.ID]interface{})
  	for _, id := range ids {
  		if _, ok := s.buckets[id]; !ok {
  			continue
  		}
  		if v, ok := s.buckets[id].Load(key); ok {
  			values[id] = v
  		}
  	}
  	return values
  }
docs: // UpNodesItems returns a map of items with the same BucketKey from all nodes that are up.