code: func (m *wsNotificationManager) NotifyBlockDisconnected(block *btcutil.Block) {
  	// As NotifyBlockDisconnected will be called by the block manager
  	// and the RPC server may no longer be running, use a select
  	// statement to unblock enqueuing the notification once the RPC
  	// server has begun shutting down.
  	select {
  	case m.queueNotification <- (*notificationBlockDisconnected)(block):
  	case <-m.quit:
  	}
  }
docs: // NotifyBlockDisconnected passes a block disconnected from the best chain
  // to the notification manager for block notification processing.