code: public synchronized void removeFromSession( HttpServletRequest request )
      {
          // This request attribute is used in persistInSession to prevent re-saving of this instance.
          request.setAttribute( REMOVING_PAGEFLOW_ATTR, this );
  
          if ( isLongLived() )
          {
              PageFlowUtils.removeLongLivedPageFlow( getModulePath(), request );
          }
          else
          {
              InternalUtils.removeCurrentPageFlow( request, getServletContext() );
          }
      }
docs: Remove this instance from the session.  When inside a page flow action, {@link #remove} may be called instead.
  This method is synchronized in order to maintain single threaded semantics for the Page Flow's
  {@link #onDestroy(javax.servlet.http.HttpSession)} lifecycle method.