code: public XidImpl getXidImpl(boolean createIfAbsent) {
          if (tc.isEntryEnabled())
              Tr.entry(tc, "getXidImpl", new Object[] { this, createIfAbsent });
  
          if (createIfAbsent && (_xid == null)) {
              // Create an XID as this transaction identifier.
              _xid = new XidImpl(new TxPrimaryKey(_localTID, Configuration.getCurrentEpoch()));
          }
  
          if (tc.isEntryEnabled())
              Tr.exit(tc, "getXidImpl", _xid);
          return (XidImpl) _xid;
      }
docs: Returns a global identifier that represents the TransactionImpl's transaction.
  
  @return The global transaction identifier.