code: func (r *Reference) Close() {
  	if !r.setClosed() {
  		// Already closed
  		return
  	}
  
  	logger.Debug("Closing reference")
  
  	r.notifyClosing()
  	r.wg.Wait()
  	r.finalize()
  }
docs: // Close ensures that the finalizer (if provided) is called.
  // Close should be called for expiring references and
  // rerences that specify finalizers.