[Misc] Support more collective_rpc return types (#21845)

Signed-off-by: Nick Hill <nhill@redhat.com>

tests/v1/engine/test_engine_core_client.py

@@ -6,8 +6,9 @@ import os
 import signal
 import time
 import uuid
+from dataclasses import dataclass
 from threading import Thread
-from typing import Optional
+from typing import Optional, Union
 from unittest.mock import MagicMock
 
 import pytest
@@ -292,6 +293,68 @@ async def test_engine_core_client_asyncio(monkeypatch: pytest.MonkeyPatch):
             client.shutdown()
 
 
+@dataclass
+class MyDataclass:
+    message: str
+
+
+# Dummy utility function to monkey-patch into engine core.
+def echo_dc(
+    self,
+    msg: str,
+    return_list: bool = False,
+) -> Union[MyDataclass, list[MyDataclass]]:
+    print(f"echo dc util function called: {msg}")
+    # Return dataclass to verify support for returning custom types
+    # (for which there is special handling to make it work with msgspec).
+    return [MyDataclass(msg) for _ in range(3)] if return_list \
+        else MyDataclass(msg)
+
+
+@pytest.mark.asyncio(loop_scope="function")
+async def test_engine_core_client_util_method_custom_return(
+        monkeypatch: pytest.MonkeyPatch):
+
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_USE_V1", "1")
+
+        # Must set insecure serialization to allow returning custom types.
+        m.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+
+        # Monkey-patch core engine utility function to test.
+        m.setattr(EngineCore, "echo_dc", echo_dc, raising=False)
+
+        engine_args = EngineArgs(model=MODEL_NAME, enforce_eager=True)
+        vllm_config = engine_args.create_engine_config(
+            usage_context=UsageContext.UNKNOWN_CONTEXT)
+        executor_class = Executor.get_class(vllm_config)
+
+        with set_default_torch_num_threads(1):
+            client = EngineCoreClient.make_client(
+                multiprocess_mode=True,
+                asyncio_mode=True,
+                vllm_config=vllm_config,
+                executor_class=executor_class,
+                log_stats=True,
+            )
+
+        try:
+            # Test utility method returning custom / non-native data type.
+            core_client: AsyncMPClient = client
+
+            result = await core_client.call_utility_async(
+                "echo_dc", "testarg2", False)
+            assert isinstance(result,
+                              MyDataclass) and result.message == "testarg2"
+            result = await core_client.call_utility_async(
+                "echo_dc", "testarg2", True)
+            assert isinstance(result, list) and all(
+                isinstance(r, MyDataclass) and r.message == "testarg2"
+                for r in result)
+        finally:
+            client.shutdown()
+
+
 @pytest.mark.parametrize(
     "multiprocessing_mode,publisher_config",
     [(True, "tcp"), (False, "inproc")],

vllm/v1/engine/__init__.py

@@ -123,6 +123,13 @@ class EngineCoreOutput(
         return self.finish_reason is not None
 
 
+class UtilityResult:
+    """Wrapper for special handling when serializing/deserializing."""
+
+    def __init__(self, r: Any = None):
+        self.result = r
+
+
 class UtilityOutput(
         msgspec.Struct,
         array_like=True,  # type: ignore[call-arg]
@@ -132,7 +139,7 @@ class UtilityOutput(
 
     # Non-None implies the call failed, result should be None.
     failure_message: Optional[str] = None
-    result: Any = None
+    result: Optional[UtilityResult] = None
 
 
 class EngineCoreOutputs(

vllm/v1/engine/core.py

@@ -36,7 +36,7 @@ from vllm.v1.core.sched.scheduler import Scheduler as V1Scheduler
 from vllm.v1.engine import (EngineCoreOutputs, EngineCoreRequest,
                             EngineCoreRequestType,
                             ReconfigureDistributedRequest, ReconfigureRankType,
-                            UtilityOutput)
+                            UtilityOutput, UtilityResult)
 from vllm.v1.engine.mm_input_cache import MirroredProcessingCache
 from vllm.v1.engine.utils import EngineHandshakeMetadata, EngineZmqAddresses
 from vllm.v1.executor.abstract import Executor
@@ -715,8 +715,8 @@ class EngineCoreProc(EngineCore):
             output = UtilityOutput(call_id)
             try:
                 method = getattr(self, method_name)
-                output.result = method(
-                    *self._convert_msgspec_args(method, args))
+                result = method(*self._convert_msgspec_args(method, args))
+                output.result = UtilityResult(result)
             except BaseException as e:
                 logger.exception("Invocation of %s method failed", method_name)
                 output.failure_message = (f"Call to {method_name} method"

vllm/v1/engine/core_client.py

@@ -552,7 +552,8 @@ def _process_utility_output(output: UtilityOutput,
     if output.failure_message is not None:
         future.set_exception(Exception(output.failure_message))
     else:
-        future.set_result(output.result)
+        assert output.result is not None
+        future.set_result(output.result.result)
 
 
 class SyncMPClient(MPClient):

vllm/v1/serial_utils.py

@@ -2,6 +2,7 @@
 # SPDX-FileCopyrightText: Copyright contributors to the vLLM project
 
 import dataclasses
+import importlib
 import pickle
 from collections.abc import Sequence
 from inspect import isclass
@@ -9,6 +10,7 @@ from types import FunctionType
 from typing import Any, Optional, Union
 
 import cloudpickle
+import msgspec
 import numpy as np
 import torch
 import zmq
@@ -22,6 +24,7 @@ from vllm.multimodal.inputs import (BaseMultiModalField,
                                     MultiModalFlatField, MultiModalKwargs,
                                     MultiModalKwargsItem,
                                     MultiModalSharedField, NestedTensors)
+from vllm.v1.engine import UtilityResult
 
 logger = init_logger(__name__)
 
@@ -46,6 +49,10 @@ def _log_insecure_serialization_warning():
                         "VLLM_ALLOW_INSECURE_SERIALIZATION=1")
 
 
+def _typestr(t: type):
+    return t.__module__, t.__qualname__
+
+
 class MsgpackEncoder:
     """Encoder with custom torch tensor and numpy array serialization.
 
@@ -122,6 +129,18 @@ class MsgpackEncoder:
                     for itemlist in mm._items_by_modality.values()
                     for item in itemlist]
 
+        if isinstance(obj, UtilityResult):
+            result = obj.result
+            if not envs.VLLM_ALLOW_INSECURE_SERIALIZATION or result is None:
+                return None, result
+            # Since utility results are not strongly typed, we also encode
+            # the type (or a list of types in the case it's a list) to
+            # help with correct msgspec deserialization.
+            cls = result.__class__
+            return _typestr(cls) if cls is not list else [
+                _typestr(type(v)) for v in result
+            ], result
+
         if not envs.VLLM_ALLOW_INSECURE_SERIALIZATION:
             raise TypeError(f"Object of type {type(obj)} is not serializable"
                             "Set VLLM_ALLOW_INSECURE_SERIALIZATION=1 to allow "
@@ -237,8 +256,33 @@ class MsgpackDecoder:
                     k: self._decode_nested_tensors(v)
                     for k, v in obj.items()
                 })
+            if t is UtilityResult:
+                return self._decode_utility_result(obj)
         return obj
 
+    def _decode_utility_result(self, obj: Any) -> UtilityResult:
+        result_type, result = obj
+        if result_type is not None:
+            if not envs.VLLM_ALLOW_INSECURE_SERIALIZATION:
+                raise TypeError("VLLM_ALLOW_INSECURE_SERIALIZATION must "
+                                "be set to use custom utility result types")
+            assert isinstance(result_type, list)
+            if len(result_type) == 2 and isinstance(result_type[0], str):
+                result = self._convert_result(result_type, result)
+            else:
+                assert isinstance(result, list)
+                result = [
+                    self._convert_result(rt, r)
+                    for rt, r in zip(result_type, result)
+                ]
+        return UtilityResult(result)
+
+    def _convert_result(self, result_type: Sequence[str], result: Any):
+        mod_name, name = result_type
+        mod = importlib.import_module(mod_name)
+        result_type = getattr(mod, name)
+        return msgspec.convert(result, result_type, dec_hook=self.dec_hook)
+
     def _decode_ndarray(self, arr: Any) -> np.ndarray:
         dtype, shape, data = arr
         # zero-copy decode. We assume the ndarray will not be kept around,