code: def list_work_units(self, work_spec_name, start=0, limit=None):
          
          return self.registry.filter(WORK_UNITS_ + work_spec_name,
                                      start=start, limit=limit)
docs: Get a dictionary of work units for some work spec.
  
          The dictionary is from work unit name to work unit definiton.
          Only work units that have not been completed ("available" or
          "pending" work units) are included.