Does DBMS_RESOURCE_MANAGER have locking mechanism?

Hi, My Oracle DB is version 11gR2 running on windows server 2003. My JDBC application is deployed in a clustered system that multiple operation can be performed on the same target at the same time. One typical operation is to set/modify consumer group.

BEGIN

DBMS_RESOURCE_MANAGER.clear_pending_area;

DBMS_RESOURCE_MANAGER.create_pending_area;

dbms_resource_manager.set_initial_consumer_group(user => 'TESTER1'

,consumer_group => 'DSS_GROUP');

DBMS_RESOURCE_MANAGER.validate_pending_area;

DBMS_RESOURCE_MANAGER.submit_pending_area;

END;

It sometimes, not always, failed with the following error message:

ORA-29370: pending area is already active

ORA-06512: at "SYS.DBMS_RMIN", line 434