code: def _hook_before_step(self):
      self.have_grad_lock.release()
      pp_rank = self.pp_rank
      stage_num = self.actual_stage_num
      co_pp_rank = (pp_rank + stage_num) % (2 * stage_num)
  
      # if current pp_rank is not the first to do step
      # wait its previous pp_rank finish step
      grads = self.get_parameter_gradients()
  
      # send
      co_worker = self.pp_rank_to_worker_rref[co_pp_rank]
      co_grads = co_worker.rpc_sync()._get_lock_gradient()
      # sync
      self.step_sync_lock.acquire()
      for i in range(len(grads)):
          grads[i] += co_grads[i]
  
imports: import threading
  from typing import Callable, Dict, List
  import torch
  from torch._C._distributed_rpc import PyRRef
  from torch.futures import Future
  from colossalai.legacy.pipeline.pipeline_process_group import ppg
  from colossalai.legacy.pipeline.rpc._pipeline_base import Phase, PipelineEngineBase, UniqueKey, WorkerBase, WorkItem
label_desc: Use image node_id 9 for calling the ChimeraWorker obj's underlying member method code with example usage: obj._hook_before_step() without return types