General mechanism to be able to rollback the transaction on some events

for specific reasons I want to reach a defined state on different databases
When I judge that this state is reached I want to put a restricted stat on these databases  :
all the pending transaction which have not committed a this moment need to be rolled back, I need a mechanism to fulfill this purpose

Is there  in ORACLE a mean to execute some code when a transaction ends ? I need a general mechanism to be able to rollback the transaction on some events

Is there any chance to get any help from you?? I do appreciate if anyone could help on this??