code: public boolean addTransactionAware(TransactionAware txAware) {
      // If the txAware is newly added, call startTx as well if there is an active transaction
      boolean added = txAwares.add(txAware);
      if (added && currentTx != null) {
        txAware.startTx(currentTx);
      }
      return added;
    }
docs: Adds a new transaction-aware to participate in the transaction.
  @param txAware the new transaction-aware