code: def receive(self):
          
          pkgidx_result_pairs = self.receive_all()
          if pkgidx_result_pairs is None:
              return
          results = [r for _, r in pkgidx_result_pairs]
          return results
docs: return a list results of all tasks.
  
          This method waits for all tasks to finish.
  
          Returns
          -------
          list
              A list of results of the tasks. The results are sorted in
              the order in which the tasks are put.