When the ProcResGroup has BufferSize=0,
- if there is a subunit in the list of write resources for the scheduling class, do not attempt to schedule the ProcResGroup.
- if there is not a subunit in the list of write resources for the scheduling class, choose a subunit to use instead of the ProcResGroup.
- having both the ProcResGroup and any of its subunits in the resources implied by a InstRW is not supported.
Used to model parallel uses from a pool of resources.