core: In astream_events v2 propagate cancel/break to the inner astream call (#22865)

- previous behavior was for the inner astream to continue running with
no interruption
- also propagate break in core runnable methods

libs/core/langchain_core/runnables/base.py

@@ -13,6 +13,7 @@ from operator import itemgetter
 from typing import (
     TYPE_CHECKING,
     Any,
+    AsyncGenerator,
     AsyncIterator,
     Awaitable,
     Callable,
@@ -79,7 +80,7 @@ from langchain_core.runnables.utils import (
     is_async_callable,
     is_async_generator,
 )
-from langchain_core.utils.aiter import atee, py_anext
+from langchain_core.utils.aiter import aclosing, atee, py_anext
 from langchain_core.utils.iter import safetee
 
 if TYPE_CHECKING:
@@ -1141,8 +1142,9 @@ class Runnable(Generic[Input, Output], ABC):
                 'Only versions "v1" and "v2" of the schema is currently supported.'
             )
 
-        async for event in event_stream:
-            yield event
+        async with aclosing(event_stream):
+            async for event in event_stream:
+                yield event
 
     def transform(
         self,
@@ -1948,7 +1950,7 @@ class Runnable(Generic[Input, Output], ABC):
                 kwargs["run_manager"] = run_manager
             context = copy_context()
             context.run(_set_config_context, child_config)
-            iterator = context.run(transformer, input_for_transform, **kwargs)  # type: ignore[arg-type]
+            iterator_ = context.run(transformer, input_for_transform, **kwargs)  # type: ignore[arg-type]
 
             if stream_handler := next(
                 (
@@ -1960,7 +1962,11 @@ class Runnable(Generic[Input, Output], ABC):
                 None,
             ):
                 # populates streamed_output in astream_log() output if needed
-                iterator = stream_handler.tap_output_aiter(run_manager.run_id, iterator)
+                iterator = stream_handler.tap_output_aiter(
+                    run_manager.run_id, iterator_
+                )
+            else:
+                iterator = iterator_
             try:
                 while True:
                     if accepts_context(asyncio.create_task):
@@ -2001,6 +2007,9 @@ class Runnable(Generic[Input, Output], ABC):
             raise
         else:
             await run_manager.on_chain_end(final_output, inputs=final_input)
+        finally:
+            if hasattr(iterator_, "aclose"):
+                await iterator_.aclose()
 
 
 class RunnableSerializable(Serializable, Runnable[Input, Output]):
@@ -3907,23 +3916,29 @@ class RunnableLambda(Runnable[Input, Output]):
 
         if is_async_generator(afunc):
             output: Optional[Output] = None
-            async for chunk in cast(
-                AsyncIterator[Output],
-                acall_func_with_variable_args(
-                    cast(Callable, afunc),
-                    input,
-                    config,
-                    run_manager,
-                    **kwargs,
-                ),
-            ):
-                if output is None:
-                    output = chunk
-                else:
-                    try:
-                        output = output + chunk  # type: ignore[operator]
-                    except TypeError:
+            async with aclosing(
+                cast(
+                    AsyncGenerator[Any, Any],
+                    acall_func_with_variable_args(
+                        cast(Callable, afunc),
+                        input,
+                        config,
+                        run_manager,
+                        **kwargs,
+                    ),
+                )
+            ) as stream:
+                async for chunk in cast(
+                    AsyncIterator[Output],
+                    stream,
+                ):
+                    if output is None:
                         output = chunk
+                    else:
+                        try:
+                            output = output + chunk  # type: ignore[operator]
+                        except TypeError:
+                            output = chunk
         else:
             output = await acall_func_with_variable_args(
                 cast(Callable, afunc), input, config, run_manager, **kwargs

libs/core/langchain_core/tracers/event_stream.py

@@ -37,7 +37,7 @@ from langchain_core.runnables.utils import (
 from langchain_core.tracers._streaming import _StreamingCallbackHandler
 from langchain_core.tracers.log_stream import LogEntry
 from langchain_core.tracers.memory_stream import _MemoryStream
-from langchain_core.utils.aiter import py_anext
+from langchain_core.utils.aiter import aclosing, py_anext
 
 if TYPE_CHECKING:
     from langchain_core.documents import Document
@@ -903,11 +903,10 @@ async def _astream_events_implementation_v2(
     async def consume_astream() -> None:
         try:
             # if astream also calls tap_output_aiter this will be a no-op
-            async for _ in event_streamer.tap_output_aiter(
-                run_id, runnable.astream(input, config, **kwargs)
-            ):
-                # All the content will be picked up
-                pass
+            async with aclosing(runnable.astream(input, config, **kwargs)) as stream:
+                async for _ in event_streamer.tap_output_aiter(run_id, stream):
+                    # All the content will be picked up
+                    pass
         finally:
             await event_streamer.send_stream.aclose()
 
@@ -942,7 +941,8 @@ async def _astream_events_implementation_v2(
             yield event
     finally:
         # Wait for the runnable to finish, if not cancelled (eg. by break)
-        try:
-            await task
-        except asyncio.CancelledError:
-            pass
+        if task.cancel():
+            try:
+                await task
+            except asyncio.CancelledError:
+                pass

libs/core/langchain_core/utils/aiter.py

@@ -5,6 +5,8 @@ MIT License
 """
 
 from collections import deque
+from contextlib import AbstractAsyncContextManager
+from types import TracebackType
 from typing import (
     Any,
     AsyncContextManager,
@@ -18,6 +20,7 @@ from typing import (
     List,
     Optional,
     Tuple,
+    Type,
     TypeVar,
     Union,
     cast,
@@ -207,3 +210,40 @@ class Tee(Generic[T]):
 
 
 atee = Tee
+
+
+class aclosing(AbstractAsyncContextManager):
+    """Async context manager for safely finalizing an asynchronously cleaned-up
+    resource such as an async generator, calling its ``aclose()`` method.
+
+    Code like this:
+
+        async with aclosing(<module>.fetch(<arguments>)) as agen:
+            <block>
+
+    is equivalent to this:
+
+        agen = <module>.fetch(<arguments>)
+        try:
+            <block>
+        finally:
+            await agen.aclose()
+
+    """
+
+    def __init__(
+        self, thing: Union[AsyncGenerator[Any, Any], AsyncIterator[Any]]
+    ) -> None:
+        self.thing = thing
+
+    async def __aenter__(self) -> Union[AsyncGenerator[Any, Any], AsyncIterator[Any]]:
+        return self.thing
+
+    async def __aexit__(
+        self,
+        exc_type: Optional[Type[BaseException]],
+        exc_value: Optional[BaseException],
+        traceback: Optional[TracebackType],
+    ) -> None:
+        if hasattr(self.thing, "aclose"):
+            await self.thing.aclose()

libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py

@@ -1,4 +1,5 @@
 """Module that contains tests for runnable.astream_events API."""
+import asyncio
 import sys
 import uuid
 from itertools import cycle
@@ -38,6 +39,7 @@ from langchain_core.runnables import (
     RunnableConfig,
     RunnableGenerator,
     RunnableLambda,
+    chain,
     ensure_config,
 )
 from langchain_core.runnables.config import get_callback_manager_for_config
@@ -45,6 +47,7 @@ from langchain_core.runnables.history import RunnableWithMessageHistory
 from langchain_core.runnables.schema import StreamEvent
 from langchain_core.runnables.utils import Input, Output
 from langchain_core.tools import tool
+from langchain_core.utils.aiter import aclosing
 from tests.unit_tests.stubs import AnyStr
 
 
@@ -2195,3 +2198,140 @@ async def test_with_explicit_config() -> None:
         for event in events
         if event["event"] == "on_chat_model_stream"
     ] == ["hello", " ", "world"]
+
+
+async def test_break_astream_events() -> None:
+    class AwhileMaker:
+        def __init__(self) -> None:
+            self.reset()
+
+        async def __call__(self, input: Any) -> Any:
+            self.started = True
+            try:
+                await asyncio.sleep(0.5)
+                return input
+            except asyncio.CancelledError:
+                self.cancelled = True
+                raise
+
+        def reset(self) -> None:
+            self.started = False
+            self.cancelled = False
+
+    alittlewhile = AwhileMaker()
+    awhile = AwhileMaker()
+    anotherwhile = AwhileMaker()
+
+    outer_cancelled = False
+
+    @chain
+    async def sequence(input: Any) -> Any:
+        try:
+            yield await alittlewhile(input)
+            yield await awhile(input)
+            yield await anotherwhile(input)
+        except asyncio.CancelledError:
+            nonlocal outer_cancelled
+            outer_cancelled = True
+            raise
+
+    # test interrupting astream_events v2
+
+    got_event = False
+    thread2: RunnableConfig = {"configurable": {"thread_id": 2}}
+    async with aclosing(
+        sequence.astream_events({"value": 1}, thread2, version="v2")
+    ) as stream:
+        async for chunk in stream:
+            if chunk["event"] == "on_chain_stream":
+                got_event = True
+                assert chunk["data"]["chunk"] == {"value": 1}
+                break
+
+    # did break
+    assert got_event
+    # did cancel outer chain
+    assert outer_cancelled
+
+    # node "alittlewhile" starts, not cancelled
+    assert alittlewhile.started is True
+    assert alittlewhile.cancelled is False
+
+    # node "awhile" starts but is cancelled
+    assert awhile.started is True
+    assert awhile.cancelled is True
+
+    # node "anotherwhile" should never start
+    assert anotherwhile.started is False
+
+
+async def test_cancel_astream_events() -> None:
+    class AwhileMaker:
+        def __init__(self) -> None:
+            self.reset()
+
+        async def __call__(self, input: Any) -> Any:
+            self.started = True
+            try:
+                await asyncio.sleep(0.5)
+                return input
+            except asyncio.CancelledError:
+                self.cancelled = True
+                raise
+
+        def reset(self) -> None:
+            self.started = False
+            self.cancelled = False
+
+    alittlewhile = AwhileMaker()
+    awhile = AwhileMaker()
+    anotherwhile = AwhileMaker()
+
+    outer_cancelled = False
+
+    @chain
+    async def sequence(input: Any) -> Any:
+        try:
+            yield await alittlewhile(input)
+            yield await awhile(input)
+            yield await anotherwhile(input)
+        except asyncio.CancelledError:
+            nonlocal outer_cancelled
+            outer_cancelled = True
+            raise
+
+    got_event = False
+
+    async def aconsume(stream: AsyncIterator[Any]) -> None:
+        nonlocal got_event
+        # here we don't need aclosing as cancelling the task is propagated
+        # to the async generator being consumed
+        async for chunk in stream:
+            if chunk["event"] == "on_chain_stream":
+                got_event = True
+                assert chunk["data"]["chunk"] == {"value": 1}
+                task.cancel()
+
+    thread2: RunnableConfig = {"configurable": {"thread_id": 2}}
+    task = asyncio.create_task(
+        aconsume(sequence.astream_events({"value": 1}, thread2, version="v2"))
+    )
+
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+    # did break
+    assert got_event
+    # did cancel outer chain
+    assert outer_cancelled
+
+    # node "alittlewhile" starts, not cancelled
+    assert alittlewhile.started is True
+    assert alittlewhile.cancelled is False
+
+    # node "awhile" starts but is cancelled
+    assert awhile.started is True
+    assert awhile.cancelled is True
+
+    # node "anotherwhile" should never start
+    assert anotherwhile.started is False