[hotfix] Fix the bug where process groups were not being properly released. (#4940)

* Fix the bug where process groups were not being properly released.

* test

* Revert "test"

This reverts commit 479900c.

Author: littsk

colossalai/cluster/process_group_mesh.py

@@ -1,3 +1,4 @@
+import gc
 import itertools
 from functools import reduce
 from operator import mul
@@ -44,6 +45,24 @@ def __init__(self, *size: int) -> None:
         self._ranks_to_group: Dict[Tuple[int, ...], ProcessGroup] = {}
         self._group_to_ranks: Dict[ProcessGroup, Tuple[int, ...]] = {}
 
+    def __del__(self):
+        r"""
+        Destructor method for the ProcessGroupMesh class.
+
+        When the ProcessGroupMesh object is deleted or goes out of scope, this method is called. It is responsible for
+        cleaning up any process groups that were created during the lifetime of the object.
+
+        Note:
+            All process groups in PyTorch are represented as global variables, and they may not be automatically destroyed
+            when the ProcessGroupMesh's lifetime ends. This method manually destroys the process groups to release
+            system resources.
+        """
+        for group in self._ranks_to_group.values():
+            dist.destroy_process_group(group)
+
+        # Manually clear all process groups to save memory
+        gc.collect()
+
     @property
     def shape(self) -> Tuple[int, ...]:
         return self._shape

colossalai/tensor/d_tensor/layout_converter.py

@@ -4,6 +4,7 @@
 from typing import Dict, List, Tuple
 
 import torch
+import torch.distributed as dist
 
 from colossalai.context.singleton_meta import SingletonMeta
 from colossalai.tensor.d_tensor.comm_spec import *
@@ -438,11 +439,58 @@ def layout_converting(
         MAX_TRANSFORM_STEPS = 20
         total_steps = 0
         transform_path = []
-        comm_action_sequence = []
+        comm_action_sequence: List[CommSpec] = []
         spec_pairs = (str(source_spec.sharding_sequence), str(target_spec.sharding_sequence))
 
         if spec_pairs in self.cached_solution:
-            return self.cached_solution[spec_pairs]
+            # Solution Cache hit
+
+            def _group_alive_check(cached_comm_action_sequence):
+                r"""
+                Check if the process groups required for sharding have been deleted by torch.distributed.destroy_process_group method.
+                If not deleted, return True; otherwise, return False.
+
+                Args:
+                    cached_comm_action_sequence (List[CommSpec]): A list of communication specifications representing actions.
+
+                Returns:
+                    bool: True if all process groups are still registered, False if at least one has been deleted.
+
+                Raises:
+                    RuntimeError: If there is an error while checking the status of a process group.
+                """
+
+                # Collect all process groups used in communication actions from the cached sequence
+                used_process_groups = [
+                    pg for comm_spec in cached_comm_action_sequence for pg in comm_spec.process_group_dict.values()
+                ]
+
+                # Check if each process group is still alive
+                for process_group in used_process_groups:
+                    try:
+                        dist.get_rank(process_group)
+                    except RuntimeError as e:
+                        # If the group is not registered, it means it has been deleted
+                        if str(e) == (
+                            f"Group {process_group} is not registered, please create group with torch.distributed.new_group API"
+                        ):
+                            return False
+                        elif str(e) == "The given group does not exist":
+                            return False
+                        else:
+                            # Re-raise the exception if it's not related to group deletion
+                            raise e
+                # All process groups are alive
+                return True
+
+            cached_transform_path, cached_comm_action_sequence = self.cached_solution[spec_pairs]
+
+            if _group_alive_check(cached_comm_action_sequence):
+                # If all process groups have not been deleted, the cache is valid
+                return cached_transform_path, cached_comm_action_sequence
+            else:
+                # If at least one process group has been deleted, the cache is invalid, so delete it
+                del self.cached_solution[spec_pairs]
 
         # We do nothing if the sharding spec is all the same.
         if source_spec.spec_diff(target_spec) == 0: