[V1][BugFix] Exit properly if engine core fails during startup (#16137)

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

requirements/test.in

@@ -5,6 +5,7 @@ pytest-forked
 pytest-asyncio
 pytest-rerunfailures
 pytest-shard
+pytest-timeout
 
 # testing utils
 awscli

requirements/test.txt

@@ -444,6 +444,7 @@ pytest==8.3.3
     #   pytest-mock
     #   pytest-rerunfailures
     #   pytest-shard
+    #   pytest-timeout
 pytest-asyncio==0.24.0
     # via -r requirements/test.in
 pytest-forked==1.6.0
@@ -454,6 +455,8 @@ pytest-rerunfailures==14.0
     # via -r requirements/test.in
 pytest-shard==0.1.2
     # via -r requirements/test.in
+pytest-timeout==2.3.1
+    # via -r requirements/test.in
 python-dateutil==2.9.0.post0
     # via
     #   botocore

tests/v1/engine/test_engine_core_client.py

@@ -3,8 +3,10 @@
 import asyncio
 import time
 import uuid
+from threading import Thread
 from typing import Optional
 
+import psutil
 import pytest
 from transformers import AutoTokenizer
 
@@ -245,3 +247,42 @@ async def test_engine_core_client_asyncio(monkeypatch: pytest.MonkeyPatch):
             await core_client.call_utility_async("echo", None, "help!")
 
         assert str(e_info.value) == "Call to echo method failed: help!"
+
+
+@pytest.mark.timeout(10)
+def test_startup_failure(monkeypatch: pytest.MonkeyPatch):
+
+    with monkeypatch.context() as m, pytest.raises(Exception) as e_info:
+        m.setenv("VLLM_USE_V1", "1")
+
+        engine_args = EngineArgs(model=MODEL_NAME)
+        vllm_config = engine_args.create_engine_config(
+            usage_context=UsageContext.UNKNOWN_CONTEXT)
+        executor_class = Executor.get_class(vllm_config)
+
+        # Start another thread to wait for engine core process to start
+        # and kill it - simulate fatal uncaught process exit.
+        this_proc = psutil.Process()
+        children_before = set(this_proc.children())
+
+        def kill_first_child():
+            while True:
+                time.sleep(0.5)
+                children = set(this_proc.children()) - children_before
+                if children:
+                    child = children.pop()
+                    print("Killing child core process", child.pid)
+                    child.kill()
+                    break
+
+        Thread(target=kill_first_child, daemon=True).start()
+
+        _core_client = EngineCoreClient.make_client(
+            multiprocess_mode=True,
+            asyncio_mode=True,
+            vllm_config=vllm_config,
+            executor_class=executor_class,
+            log_stats=True,
+        )
+
+    assert "Engine core initialization failed" in str(e_info.value)

vllm/v1/engine/core_client.py

@@ -411,10 +411,21 @@ class MPClient(EngineCoreClient):
 
         # Wait for engine core process(es) to send ready messages.
         identities = set(eng.index for eng in self.resources.core_engines)
+        poller = zmq.Poller()
+        poller.register(sync_input_socket, zmq.POLLIN)
+        for eng in self.resources.core_engines:
+            poller.register(eng.proc_handle, zmq.POLLIN)
         while identities:
-            while not sync_input_socket.poll(timeout=STARTUP_POLL_PERIOD_MS):
-                logger.info("Waiting for %d core engine proc(s) to start: %s",
-                            len(identities), identities)
+            events = poller.poll(STARTUP_POLL_PERIOD_MS)
+            if not events:
+                logger.debug("Waiting for %d core engine proc(s) to start: %s",
+                             len(identities), identities)
+                continue
+            if len(events) > 1 or events[0][0] != sync_input_socket:
+                # One of the core processes exited.
+                raise RuntimeError("Engine core initialization failed. "
+                                   "See root cause above.")
+
             eng_id_bytes, msg = sync_input_socket.recv_multipart()
             eng_id = int.from_bytes(eng_id_bytes, byteorder="little")
             if eng_id not in identities:
@@ -424,12 +435,6 @@ class MPClient(EngineCoreClient):
             logger.info("Core engine process %d ready.", eng_id)
             identities.discard(eng_id)
 
-        # Double check that the process are running.
-        for engine in self.resources.core_engines:
-            proc = engine.proc_handle.proc
-            if proc.exitcode is not None:
-                raise RuntimeError(f"Engine proc {proc.name} not running")
-
     def _init_core_engines(
         self,
         vllm_config: VllmConfig,

vllm/v1/utils.py

 # SPDX-License-Identifier: Apache-2.0
 
-import multiprocessing
 import os
 import weakref
 from collections import defaultdict
 from collections.abc import Sequence
+from multiprocessing import Process
 from typing import (TYPE_CHECKING, Any, Callable, Generic, Optional, TypeVar,
                     Union, overload)
 
@@ -112,20 +112,23 @@ class BackgroundProcHandle:
         process_kwargs["output_path"] = output_path
 
         # Run busy loop in background process.
-        self.proc = context.Process(target=target_fn,
-                                    kwargs=process_kwargs,
-                                    name=process_name)
+        self.proc: Process = context.Process(target=target_fn,
+                                             kwargs=process_kwargs,
+                                             name=process_name)
         self._finalizer = weakref.finalize(self, shutdown, self.proc,
                                            input_path, output_path)
         self.proc.start()
 
+    def fileno(self):
+        return self.proc.sentinel
+
     def shutdown(self):
         self._finalizer()
 
 
 # Note(rob): shutdown function cannot be a bound method,
 # else the gc cannot collect the object.
-def shutdown(proc: multiprocessing.Process, input_path: str, output_path: str):
+def shutdown(proc: Process, input_path: str, output_path: str):
     # Shutdown the process.
     if proc.is_alive():
         proc.terminate()