code: def receive_all(self):
          
          if not self.isopen:
              logger = logging.getLogger(__name__)
              logger.warning('the drop box is not open')
              return
          return self.dropbox.receive()
docs: return a list of pairs of IDs and results of all tasks.
  
          This method waits for all tasks to finish.
  
          Returns
          -------
          list
              A list of pairs of IDs and results