Add lock for using global config enum weak map (#11920)

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libs/langchain/langchain/schema/runnable/configurable.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import enum
+import threading
 from abc import abstractmethod
 from typing import (
     Any,
@@ -270,6 +271,8 @@ _enums_for_spec: WeakValueDictionary[
     Type[StrEnum],
 ] = WeakValueDictionary()
 
+_enums_for_spec_lock = threading.Lock()
+
 
 class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
     which: ConfigurableField
@@ -280,12 +283,16 @@ class RunnableConfigurableAlternatives(DynamicRunnable[Input, Output]):
 
     @property
     def config_specs(self) -> Sequence[ConfigurableFieldSpec]:
+        with _enums_for_spec_lock:
             if which_enum := _enums_for_spec.get(self.which):
                 pass
             else:
                 which_enum = StrEnum(  # type: ignore[call-overload]
                     self.which.name or self.which.id,
-                ((v, v) for v in list(self.alternatives.keys()) + [self.default_key]),
+                    (
+                        (v, v)
+                        for v in list(self.alternatives.keys()) + [self.default_key]
+                    ),
                 )
                 _enums_for_spec[self.which] = cast(Type[StrEnum], which_enum)
         return [
@@ -325,6 +332,7 @@ def make_options_spec(
     spec: Union[ConfigurableFieldSingleOption, ConfigurableFieldMultiOption],
     description: Optional[str],
 ) -> ConfigurableFieldSpec:
+    with _enums_for_spec_lock:
         if enum := _enums_for_spec.get(spec):
             pass
         else: