The implementation of this method should gather and hold required resources (locks, disk
space, etc) to satisfy the Procedures barrier condition. For example, this would be where
to make all the regions on a RS on the quiescent for an procedure that required all regions
to be globally quiesed.
Users should override this method. If a quiescent is not required, this is overkill but
can still be used to execute a procedure on all members and to propagate any exceptions.
The implementation of this method should act with the assumption that the barrier condition
has been satisfied. Continuing the previous example, a condition could be that all RS's
globally have been quiesced, and procedures that require this precondition could be
The implementation should also collect the result of the subprocedure as data to be returned
to the coordinator upon successful completion.
Users should override this method.