feat(singleton): ensure singleton thread safety and no performance degradation (#205)

Author: zigzagcai

internlm/utils/common.py

@@ -5,6 +5,7 @@
 import inspect
 import os
 import random
+import threading
 from abc import ABC, abstractmethod
 from contextlib import contextmanager
 from datetime import datetime
@@ -169,18 +170,27 @@ def __call__(self, batch_count):
 
 class SingletonMeta(type):
     """
-    Singleton Meta.
+    Thread-safe Singleton Meta with double-checked locking.
+    Reference: https://en.wikipedia.org/wiki/Double-checked_locking
     """
 
     _instances = {}
+    _lock = threading.Lock()
 
     def __call__(cls, *args, **kwargs):
+        # First check (without locking) for performance reasons
         if cls not in cls._instances:
-            cls._instances[cls] = super().__call__(*args, **kwargs)
+            # Acquire a lock before proceeding to the second check
+            with cls._lock:
+                # Second check with lock held to ensure thread safety
+                if cls not in cls._instances:
+                    instance = super().__call__(*args, **kwargs)
+                    cls._instances[cls] = instance
         else:
             assert (
                 len(args) == 0 and len(kwargs) == 0
-            ), f"{cls.__name__} is a singleton class and a instance has been created."
+            ), f"{cls.__name__} is a singleton class and an instance has been created."
+
         return cls._instances[cls]