code: def _initialize_process_group(self):
      stage_num = self.get_stage_num()
      if stage_num == 1:
          return
      device = self.device
      world_size = self.get_world_size()
      rank = self.get_global_rank()
      backend = "nccl" if device == "cuda" else "gloo"
      dist.init_process_group(
          backend,
          world_size=world_size,
          rank=rank,
          group_name="main_group",
      )
  
imports: import threading
  from typing import List
  import torch.distributed
  from torch.distributed import rpc
  from colossalai.legacy.tensor import ProcessGroup
label_desc: Use image node_id 3 for calling the PipelineProcessGroup obj's underlying member method code with example usage: obj._initialize_process_group() without return types