code: @Override
      public void begin()
      {
          if (isActive())
          {
              throw new IllegalStateException("Transaction is already active");
          }
          else
          {
              this.coordinator = ((EntityManagerImpl) entityManager).getPersistenceDelegator().getCoordinator();
              ((EntityManagerImpl) entityManager).getPersistenceDelegator().begin(); // transaction
                                                                                     // de-marcation.
              this.coordinator.coordinate(TxAction.BEGIN);
          }
      }
docs: /*
  (non-Javadoc)
  
  @see javax.persistence.EntityTransaction#begin()