Javadoc
Enlist the specified participant with current transaction such that it
will participate in the 2PC protocol; a unique identifier for the
participant is also required. If there is no transaction associated with
the invoking thread then the UnknownTransactionException exception is
thrown. If the coordinator already has a participant enrolled with the
same identifier, then AlreadyRegisteredException will be thrown. If the
transaction is not in a state where participants can be enrolled (e.g.,
it is terminating) then WrongStateException will be thrown.