not. If True, this will 1) wait until there is no pending system
      messages for "UserRRefs" and delete them; 2) block until all
      local and remote RPC processes have reached this method and wait
      for all outstanding work to complete.
Example::
      Make sure that "MASTER_ADDR" and "MASTER_PORT" are set properly
      on both workers. Refer to "init_process_group()" API for more
      details. For example,
  export MASTER_ADDR=localhost export MASTER_PORT=5678

  Then run the following code in two different processes:

  >>> # On worker 0:
  >>> import torch
  >>> import torch.distributed.rpc as rpc
  >>> rpc.init_rpc("worker0", rank=0, world_size=2)
  >>> # do some work
  >>> result = rpc.rpc_sync("worker1", torch.add, args=(torch.ones(1), 1))
  >>> # ready to shutdown
  >>> rpc.shutdown()

  >>> # On worker 1:
  >>> import torch.distributed.rpc as rpc
  >>> rpc.init_rpc("worker1", rank=1, world_size=2)
