code: def pre_bwd_exec(self, module: torch.nn.Module, input_, output):
      if self._enable:
          self.tracer.sample()
  
imports: import os
  import threading
  import time
  from enum import Enum
  from typing import List
  import torch
  from colossalai.gemini.ophooks import BaseOpHook
  from colossalai.gemini.stateful_tensor import StatefulTensor
  from colossalai.legacy.engine import Engine
  from colossalai.legacy.utils.profiler.extention import ProfilerExtension
label_desc: Use image node_id 4 for calling the StatefulTensorMemoryTracerHook obj's underlying member method code with example usage: obj.pre_bwd_exec(module, input_, output) without return types