Swap DCP restore ad-hoc gloo pg creation with context manager (#903)

Summary: Pull Request resolved: #903

Reviewed By: JKSenthil

Differential Revision: D63268179

fbshipit-source-id: 47294a0fd8c560d7abb3db426305ec8b522c0432

Author: diego-urgell

torchtnt/framework/callbacks/dcp_saver.py

@@ -9,7 +9,6 @@
 import logging
 import time
 from concurrent.futures import Future
-from datetime import timedelta
 from typing import Any, Dict, Iterable, List, Optional, Union
 
 import torch.distributed as dist
@@ -45,6 +44,7 @@
 )
 from torchtnt.framework.utils import get_timing_context
 from torchtnt.utils.checkpoint import BestCheckpointConfig
+from torchtnt.utils.distributed import get_or_create_gloo_pg
 from torchtnt.utils.rank_zero_log import rank_zero_info, rank_zero_warn
 from torchtnt.utils.stateful import MultiStateful, Stateful
 
@@ -271,23 +271,6 @@ def restore_with_id(
             storage_reader: Instance of StorageReader used to perform reads. If this is not specified, it will automatically infer
                             the reader based on the checkpoint_id. If checkpoint_id is also None, an exception will be raised. (Default: ``None``)
         """
-
-        # use gloo pg if available
-        gloo_pg_created = False
-        if dist.is_initialized():
-            pg = dist.group.WORLD if process_group is None else process_group
-
-            if dist.get_backend(pg) != dist.Backend.GLOO:
-                rank_zero_info(
-                    "Creating new gloo process group for loading checkpoint."
-                )
-                pg = dist.new_group(
-                    timeout=timedelta(seconds=3600), backend=dist.Backend.GLOO
-                )
-                gloo_pg_created = True
-        else:
-            pg = process_group
-
         restore_options = restore_options or RestoreOptions()
         app_state = _prepare_app_state_for_restore(unit, restore_options)
         checkpoint_id = str(checkpoint_id)
@@ -321,22 +304,19 @@ def restore_with_id(
                         "train_dataloader was passed to `restore` but no train dataloader exists in the Snapshot"
                     )
 
-        dcp.load(
-            {"app_state": MultiStateful(app_state)},
-            checkpoint_id=checkpoint_id,
-            storage_reader=storage_reader,
-            planner=planner,
-            process_group=pg,
-        )
+        with get_or_create_gloo_pg(candidate_pg=process_group) as pg:
+            dcp.load(
+                {"app_state": MultiStateful(app_state)},
+                checkpoint_id=checkpoint_id,
+                storage_reader=storage_reader,
+                planner=planner,
+                process_group=pg,
+            )
 
         rank_zero_info(
             f"Restored snapshot for checkpoint_id: {checkpoint_id}", logger=logger
         )
 
-        # destroy gloo pg if created, its sole purpose was for checkpoint restore
-        if gloo_pg_created:
-            dist.destroy_process_group(pg)
-
     def _generate_checkpoint_and_upkeep(
         self, state: State, unit: Union[TTrainUnit, TEvalUnit], hook: str
     ) -> bool: