code: def forward(self, input):
      bar = yield pop("bar")
      return input + bar
  
imports: from torch import nn
  from torch.distributed.pipeline.sync.skip import Namespace, pop, skippable, stash
  from torch.distributed.pipeline.sync.skip.layout import inspect_skip_layout
  from torch.testing._internal.common_utils import run_tests
label_desc: Use image node_id 1 for calling the PopBar obj's underlying member method code with example usage: obj.forward(input) and returns: unknown