code: def batch_start(job, input_args):
      
      shared_files = ['ref.fa', 'ref.fa.amb', 'ref.fa.ann', 'ref.fa.bwt', 'ref.fa.pac', 'ref.fa.sa', 'ref.fa.fai']
      shared_ids = {}
      for fname in shared_files:
          url = input_args[fname]
          shared_ids[fname] = job.addChildJobFn(download_from_url, url, fname).rv()
      job.addFollowOnJobFn(spawn_batch_jobs, shared_ids, input_args)
docs: Downloads shared files that are used by all samples for alignment and places them in the jobstore.