zero init ctx receives a dp process group (#471)

colossalai/zero/init_ctx/init_context.py

 import functools
+from typing import Optional
 
 import torch
+from colossalai.context.parallel_mode import ParallelMode
+from colossalai.core import global_context as gpc
 from colossalai.utils.memory_tracer.model_data_memtracer import \
     GLOBAL_MODEL_DATA_TRACER
 from colossalai.zero.shard_utils import BaseShardStrategy
 from colossalai.zero.sharded_model._zero3_utils import cast_tensor_to_fp16
 from colossalai.zero.sharded_param import ShardedParamV2
+from torch.distributed import ProcessGroup
 
 # Inserts _post_init_method at the end of init method
 
@@ -103,8 +107,9 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
                  shard_strategy: BaseShardStrategy,
                  shard_param: bool = False,
                  shard_grad: bool = False,
-                 rm_torch_payload_on_the_fly=False,
-                 model_numel_tensor: torch.Tensor = torch.zeros(1, dtype=torch.int)):
+                 rm_torch_payload_on_the_fly: bool = False,
+                 model_numel_tensor: torch.Tensor = torch.zeros(1, dtype=torch.int),
+                 dp_process_group: Optional[ProcessGroup] = None):
         super().__init__()
         self.convert_fp16 = convert_fp16
         self.target_device = target_device
@@ -115,6 +120,7 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
         self.rm_torch_payload_on_the_fly = False
         self.initialized_param_list = []
         self.model_numel_tensor = model_numel_tensor
+        self.dp_process_group = dp_process_group or gpc.get_group(ParallelMode.DATA)
 
     def _post_context_exec(self):
         """The callback function when the context exits.
@@ -154,10 +160,10 @@ class ZeroInitContext(InsertPostInitMethodToModuleSubClasses):
             self.initialized_param_list.append(param)
 
             if self.shard_param:
-                self.shard_strategy.shard(tensor_list=[param.col_attr._data_sharded_tensor])
+                self.shard_strategy.shard([param.col_attr._data_sharded_tensor], self.dp_process_group)
                 GLOBAL_MODEL_DATA_TRACER.add_tensor(param.col_attr._data_sharded_tensor.payload)
             # if param.col_attr.grad and self.shard_grad:
-            #     self.shard_strategy.shard(tensor_list=[param.col_attr._grad_sharded_tensor])
+            #     self.shard_strategy.shard([param.col_attr._grad_sharded_tensor], self.dp_process_group)
             #     GLOBAL_MODEL_DATA_TRACER.add_tensor(param.col_attr._grad_sharded_tensor.payload)
         # We must cast buffers
         # If we use BN, buffers may be on CPU and Float