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 implemented here.
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.