core: run_in_executor: Wrap StopIteration in RuntimeError (#22997)

- StopIteration can't be set on an asyncio.Future it raises a TypeError
and leaves the Future pending forever so we need to convert it to a
RuntimeError

libs/core/langchain_core/runnables/config.py

@@ -542,13 +542,21 @@ async def run_in_executor(
     Returns:
         Output: The output of the function.
     """
+
+    def wrapper() -> T:
+        try:
+            return func(*args, **kwargs)
+        except StopIteration as exc:
+            # StopIteration can't be set on an asyncio.Future
+            # it raises a TypeError and leaves the Future pending forever
+            # so we need to convert it to a RuntimeError
+            raise RuntimeError from exc
+
     if executor_or_config is None or isinstance(executor_or_config, dict):
         # Use default executor with context copied from current context
         return await asyncio.get_running_loop().run_in_executor(
             None,
-            cast(Callable[..., T], partial(copy_context().run, func, *args, **kwargs)),
+            cast(Callable[..., T], partial(copy_context().run, wrapper)),
         )
 
-    return await asyncio.get_running_loop().run_in_executor(
+    return await asyncio.get_running_loop().run_in_executor(executor_or_config, wrapper)
-        executor_or_config, partial(func, **kwargs), *args
-    )

libs/core/tests/unit_tests/runnables/test_config.py

@@ -1,10 +1,16 @@
 from typing import Any, cast
 
+import pytest
+
 from langchain_core.callbacks.manager import CallbackManager
 from langchain_core.callbacks.stdout import StdOutCallbackHandler
 from langchain_core.callbacks.streaming_stdout import StreamingStdOutCallbackHandler
 from langchain_core.runnables import RunnableBinding, RunnablePassthrough
-from langchain_core.runnables.config import RunnableConfig, merge_configs
+from langchain_core.runnables.config import (
+    RunnableConfig,
+    merge_configs,
+    run_in_executor,
+)
 from langchain_core.tracers.stdout import ConsoleCallbackHandler
 
 
@@ -43,3 +49,14 @@ def test_config_arbitrary_keys() -> None:
     config = cast(RunnableBinding, bound).config
 
     assert config.get("my_custom_key") == "my custom value"
+
+
+async def test_run_in_executor() -> None:
+    def raises_stop_iter() -> Any:
+        return next(iter([]))
+
+    with pytest.raises(StopIteration):
+        raises_stop_iter()
+
+    with pytest.raises(RuntimeError):
+        await run_in_executor(None, raises_stop_iter)