code: func (pb *Block) Close() error {
  	pb.mtx.Lock()
  	pb.closing = true
  	pb.mtx.Unlock()
  
  	pb.pendingReaders.Wait()
  
  	var merr tsdb_errors.MultiError
  
  	merr.Add(pb.chunkr.Close())
  	merr.Add(pb.indexr.Close())
  	merr.Add(pb.tombstones.Close())
  
  	return merr.Err()
  }
docs: // Close closes the on-disk block. It blocks as long as there are readers reading from the block.