code: def _get_external_workers(worker):
      
      worker_that_blocked_task = collections.defaultdict(set)
      get_work_response_history = worker._get_work_response_history
      for get_work_response in get_work_response_history:
          if get_work_response['task_id'] is None:
              for running_task in get_work_response['running_tasks']:
                  other_worker_id = running_task['worker']
                  other_task_id = running_task['task_id']
                  other_task = worker._scheduled_tasks.get(other_task_id)
                  if other_worker_id == worker._id or not other_task:
                      continue
                  worker_that_blocked_task[other_worker_id].add(other_task)
      return worker_that_blocked_task
docs: This returns a dict with a set of tasks for all of the other workers