code: def build_mp(b, stage, source_name, force):
      
  
      source = b.source(source_name)
  
      with b.progress.start('build_mp',stage,message="MP build", source=source) as ps:
          ps.add(message='Running source {}'.format(source.name), source=source, state='running')
          r = b.build_source(stage, source, ps, force)
  
      return r
docs: Ingest a source, using only arguments that can be pickled, for multiprocessing access