core[patch]: Add missing cache for create_model (#26173)

It makes a big difference for performance.

libs/core/langchain_core/runnables/utils.py

@@ -712,7 +712,7 @@ _SchemaConfig = ConfigDict(arbitrary_types_allowed=True, frozen=True)
 NO_DEFAULT = object()
 
 
-def create_base_class(
+def _create_root_model(
     name: str, type_: Any, default_: object = NO_DEFAULT
 ) -> Type[BaseModel]:
     """Create a base class."""
@@ -765,6 +765,15 @@ def create_base_class(
     return cast(Type[BaseModel], custom_root_type)
 
 
+@lru_cache(maxsize=256)
+def _create_root_model_cached(
+    __model_name: str,
+    type_: Any,
+    default_: object = NO_DEFAULT,
+) -> Type[BaseModel]:
+    return _create_root_model(__model_name, type_, default_)
+
+
 def create_model(
     __model_name: str,
     **field_definitions: Any,
@@ -789,9 +798,15 @@ def create_model(
 
         arg = field_definitions["__root__"]
         if isinstance(arg, tuple):
-            named_root_model = create_base_class(__model_name, arg[0], arg[1])
+            kwargs = {"type_": arg[0], "default_": arg[1]}
         else:
-            named_root_model = create_base_class(__model_name, arg)
+            kwargs = {"type_": arg}
+
+        try:
+            named_root_model = _create_root_model_cached(__model_name, **kwargs)
+        except TypeError:
+            # something in the arguments into _create_root_model_cached is not hashable
+            named_root_model = _create_root_model(__model_name, **kwargs)
         return named_root_model
     try:
         return _create_model_cached(__model_name, **field_definitions)

libs/core/tests/unit_tests/language_models/chat_models/test_benchmark.py

@@ -0,0 +1,21 @@
+import time
+from itertools import cycle
+
+from langchain_core.language_models import GenericFakeChatModel
+
+
+def test_benchmark_model() -> None:
+    """Add rate limiter."""
+    tic = time.time()
+
+    model = GenericFakeChatModel(
+        messages=cycle(["hello", "world", "!"]),
+    )
+
+    for _ in range(1_000):
+        model.invoke("foo")
+    toc = time.time()
+
+    # Verify that the time taken to run the loop is less than 1 seconds
+
+    assert (toc - tic) < 1