Merge pull request #1732 from langchain-ai/nc/16sep/stream-selected

perf: In PregelLoop, only emit stream values requested by caller

libs/langgraph/langgraph/pregel/__init__.py

@@ -73,7 +73,7 @@
 )
 from langgraph.pregel.debug import tasks_w_writes
 from langgraph.pregel.io import read_channels
-from langgraph.pregel.loop import AsyncPregelLoop, SyncPregelLoop
+from langgraph.pregel.loop import AsyncPregelLoop, StreamProtocol, SyncPregelLoop
 from langgraph.pregel.manager import AsyncChannelsManager, ChannelsManager
 from langgraph.pregel.read import PregelNode
 from langgraph.pregel.retry import RetryPolicy
@@ -1148,15 +1148,14 @@ def stream(
         def output() -> Iterator:
             while stream:
                 ns, mode, payload = stream.popleft()
-                if mode in stream_modes:
-                    if subgraphs and isinstance(stream_mode, list):
-                        yield (tuple(ns.split(NS_SEP)) if ns else (), mode, payload)
-                    elif isinstance(stream_mode, list):
-                        yield (mode, payload)
-                    elif subgraphs:
-                        yield (tuple(ns.split(NS_SEP)) if ns else (), payload)
-                    else:
-                        yield payload
+                if subgraphs and isinstance(stream_mode, list):
+                    yield (ns, mode, payload)
+                elif isinstance(stream_mode, list):
+                    yield (mode, payload)
+                elif subgraphs:
+                    yield (ns, payload)
+                else:
+                    yield payload
 
         config = ensure_config(self.config, config)
         callback_manager = get_callback_manager_for_config(config)
@@ -1192,7 +1191,7 @@ def output() -> Iterator:
 
             with SyncPregelLoop(
                 input,
-                stream=stream.append,
+                stream=StreamProtocol(stream.append, stream_modes),
                 config=config,
                 store=self.store,
                 checkpointer=checkpointer,
@@ -1329,15 +1328,14 @@ async def astream(
         def output() -> Iterator:
             while stream:
                 ns, mode, payload = stream.popleft()
-                if mode in stream_modes:
-                    if subgraphs and isinstance(stream_mode, list):
-                        yield (tuple(ns.split(NS_SEP)) if ns else (), mode, payload)
-                    elif isinstance(stream_mode, list):
-                        yield (mode, payload)
-                    elif subgraphs:
-                        yield (tuple(ns.split(NS_SEP)) if ns else (), payload)
-                    else:
-                        yield payload
+                if subgraphs and isinstance(stream_mode, list):
+                    yield (ns, mode, payload)
+                elif isinstance(stream_mode, list):
+                    yield (mode, payload)
+                elif subgraphs:
+                    yield (ns, payload)
+                else:
+                    yield payload
 
         config = ensure_config(self.config, config)
         callback_manager = get_async_callback_manager_for_config(config)
@@ -1381,7 +1379,7 @@ def output() -> Iterator:
             )
             async with AsyncPregelLoop(
                 input,
-                stream=stream.append,
+                stream=StreamProtocol(stream.append, stream_modes),
                 config=config,
                 store=self.store,
                 checkpointer=checkpointer,

libs/langgraph/langgraph/pregel/loop.py

@@ -9,11 +9,11 @@
     Callable,
     ContextManager,
     Iterable,
+    Iterator,
     List,
     Literal,
     Mapping,
     Optional,
-    Protocol,
     Sequence,
     Tuple,
     Type,
@@ -24,7 +24,7 @@
 
 from langchain_core.callbacks import AsyncParentRunManager, ParentRunManager
 from langchain_core.runnables import RunnableConfig
-from typing_extensions import Self
+from typing_extensions import ParamSpec, Self
 
 from langgraph.channels.base import BaseChannel
 from langgraph.checkpoint.base import (
@@ -48,6 +48,7 @@
     ERROR,
     INPUT,
     INTERRUPT,
+    NS_SEP,
     SCHEDULED,
     TAG_HIDDEN,
     TASKS,
@@ -99,23 +100,37 @@
 from langgraph.utils.config import patch_configurable
 
 V = TypeVar("V")
+P = ParamSpec("P")
 INPUT_DONE = object()
 INPUT_RESUMING = object()
 EMPTY_SEQ = ()
 SPECIAL_CHANNELS = (ERROR, INTERRUPT, SCHEDULED)
 
 
-class StreamProtocol(Protocol):
-    def __call__(self, values: Iterable[Tuple[str, str, Any]]) -> None: ...
+class StreamProtocol:
+    __slots__ = ("modes", "__call__")
+
+    modes: Sequence[Literal["values", "updates", "debug"]]
+
+    __call__: Callable[[Iterable[Tuple[str, str, Any]]], None]
+
+    def __init__(
+        self,
+        __call__: Callable[[Iterable[Tuple[str, str, Any]]], None],
+        modes: Sequence[Literal["values", "updates", "debug"]],
+    ) -> None:
+        self.__call__ = __call__
+        self.modes = modes
 
 
 class DuplexStream(StreamProtocol):
-    def __init__(self, *queues: StreamProtocol) -> None:
-        self.queues = queues
+    def __init__(self, *streams: StreamProtocol) -> None:
+        def __call__(value: Tuple[str, str, Any]) -> None:
+            for stream in streams:
+                if value[1] in stream.modes:
+                    stream(value)
 
-    def __call__(self, value: Tuple[str, str, Any]) -> None:
-        for queue in self.queues:
-            queue(value)
+        super().__init__(__call__, {mode for s in streams for mode in s.modes})
 
 
 class PregelLoop:
@@ -150,6 +165,7 @@ class PregelLoop:
     channels: Mapping[str, BaseChannel]
     managed: ManagedValueMapping
     checkpoint: Checkpoint
+    checkpoint_ns: tuple[str, ...]
     checkpoint_config: RunnableConfig
     checkpoint_metadata: CheckpointMetadata
     checkpoint_pending_writes: List[PendingWrite]
@@ -217,6 +233,11 @@ def __init__(
             )
         else:
             self.checkpoint_config = config
+        self.checkpoint_ns = (
+            tuple(self.config["configurable"].get("checkpoint_ns").split(NS_SEP))
+            if self.config["configurable"].get("checkpoint_ns")
+            else ()
+        )
 
     def put_writes(self, task_id: str, writes: Sequence[tuple[str, Any]]) -> None:
         """Put writes for a task, to be read by the next tick."""
@@ -293,8 +314,7 @@ def tick(
                 self._update_mv(key, values)
             # produce values output
             self._emit(
-                (self.config["configurable"].get("checkpoint_ns", ""), "values", v)
-                for v in map_output_values(self.output_keys, writes, self.channels)
+                "values", map_output_values, self.output_keys, writes, self.channels
             )
             # clear pending writes
             self.checkpoint_pending_writes.clear()
@@ -344,17 +364,16 @@ def tick(
         # produce debug output
         if self._checkpointer_put_after_previous is not None:
             self._emit(
-                (self.config["configurable"].get("checkpoint_ns", ""), "debug", v)
-                for v in map_debug_checkpoint(
-                    self.step - 1,  # printing checkpoint for previous step
-                    self.checkpoint_config,
-                    self.channels,
-                    self.stream_keys,
-                    self.checkpoint_metadata,
-                    self.checkpoint,
-                    self.tasks.values(),
-                    self.checkpoint_pending_writes,
-                )
+                "debug",
+                map_debug_checkpoint,
+                self.step - 1,  # printing checkpoint for previous step
+                self.checkpoint_config,
+                self.channels,
+                self.stream_keys,
+                self.checkpoint_metadata,
+                self.checkpoint,
+                self.tasks.values(),
+                self.checkpoint_pending_writes,
             )
 
         # if no more tasks, we're done
@@ -413,10 +432,7 @@ def tick(
                 return False
 
         # produce debug output
-        self._emit(
-            (self.config["configurable"].get("checkpoint_ns", ""), "debug", v)
-            for v in map_debug_tasks(self.step, self.tasks.values())
-        )
+        self._emit("debug", map_debug_tasks, self.step, self.tasks.values())
 
         # debug flag
         if self.debug:
@@ -444,8 +460,7 @@ def _first(self, *, input_keys: Union[str, Sequence[str]]) -> None:
                     self.checkpoint["versions_seen"][INTERRUPT][k] = version
             # produce values output
             self._emit(
-                (self.config["configurable"].get("checkpoint_ns", ""), "values", v)
-                for v in map_output_values(self.output_keys, True, self.channels)
+                "values", map_output_values, self.output_keys, True, self.channels
             )
         # map inputs to channel updates
         elif input_writes := deque(map_input(input_keys, self.input)):
@@ -563,11 +578,19 @@ def _suppress_interrupt(
             # suppress interrupt
             return True
 
-    def _emit(self, values: Sequence[tuple[str, str, Any]]) -> None:
+    def _emit(
+        self,
+        mode: str,
+        values: Callable[P, Iterator[Any]],
+        *args: P.args,
+        **kwargs: P.kwargs,
+    ) -> None:
         if self.stream is None:
             return
-        for v in values:
-            self.stream(v)
+        if mode not in self.stream.modes:
+            return
+        for v in values(*args, **kwargs):
+            self.stream((self.checkpoint_ns, mode, v))
 
     def _output_writes(
         self, task_id: str, writes: Sequence[tuple[str, Any]], *, cached: bool = False
@@ -579,17 +602,19 @@ def _output_writes(
                 return
             if writes[0][0] != ERROR and writes[0][0] != INTERRUPT:
                 self._emit(
-                    (self.config["configurable"].get("checkpoint_ns", ""), "updates", v)
-                    for v in map_output_updates(
-                        self.output_keys, [(task, writes)], cached
-                    )
+                    "updates",
+                    map_output_updates,
+                    self.output_keys,
+                    [(task, writes)],
+                    cached,
                 )
             if not cached:
                 self._emit(
-                    (self.config["configurable"].get("checkpoint_ns", ""), "debug", v)
-                    for v in map_debug_task_results(
-                        self.step, (task, writes), self.stream_keys
-                    )
+                    "debug",
+                    map_debug_task_results,
+                    self.step,
+                    (task, writes),
+                    self.stream_keys,
                 )