code: @Override
      public void enlist() throws ResourceException {
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) { 
              Tr.entry(this, tc, "enlist");
          }
  
          // Enlist a one phase resource representing RRS.
          if (!enlisted) { 
              int dummyInt = -1;
              try {
                  rrsXAResource = mcWrapper.enlistRRSXAResource(dummyInt, dummyInt);
              } catch (Throwable t) {
                  throw new ResourceException(t);
              }
          }
          // Indicate that the  ManagedConnection that this transaction
          // wrapper is associated with is "dirty" (i.e, the managed
          // connection is involved in the transaction.
          enlisted = true;
          if (TraceComponent.isAnyTracingEnabled() && tc.isEntryEnabled()) { 
              Tr.exit(this, tc, "enlist");
          }
      }
docs: Enlist
  
  NOTE: In the case of RRSTransactional support, we will simply
  set the enlist indicator on. However, the real enlistment
  on the transaction is actually done by the backend
  Resource Manager. Thus, enlistment is really deferred
  until the backend Resource Manager receives the context
  from the connector at which time it registers an interest
  in the transaction using RRS services.