[Bugfix] Escalate diffusion worker shutdown and retain survivors

tests/diffusion/test_multiproc_engine_concurrency.py

@@ -4,8 +4,10 @@
 import asyncio
 import multiprocessing as mp
 import queue
+import signal
 import threading
 import time
+import weakref
 from types import SimpleNamespace
 from unittest.mock import MagicMock, Mock
 
@@ -1330,6 +1332,7 @@ def test_worker_joins_share_one_global_deadline(self, monkeypatch):
         class FakeProcess:
             def __init__(self, name):
                 self.name = name
+                self.pid = 123
                 self.alive = True
                 self.terminated = False
                 self.join_timeouts = []
@@ -1358,6 +1361,132 @@ def terminate(self):
         assert first.terminated and second.terminated
         assert not first.is_alive() and not second.is_alive()
 
+    @pytest.mark.parametrize("cooperative", [False, True])
+    def test_real_workers_exit_and_are_reaped(self, monkeypatch, cooperative):
+        from vllm_omni.diffusion.executor import multiproc_executor as executor_module
+
+        ctx = mp.get_context("fork")
+        ready, stop = ctx.Event(), ctx.Event()
+
+        def run_worker():
+            signal.signal(signal.SIGTERM, signal.SIG_IGN)
+            ready.set()
+            stop.wait()
+
+        dead = ctx.Process(target=lambda: None)
+        worker = ctx.Process(target=run_worker)
+        monkeypatch.setattr(executor_module, "_WORKER_SHUTDOWN_GRACE_S", 0.2)
+        monkeypatch.setattr(executor_module, "_WORKER_TERMINATE_GRACE_S", 0.1)
+        monkeypatch.setattr(executor_module, "_WORKER_KILL_GRACE_S", 5.0, raising=False)
+        dead.start()
+        worker.start()
+        try:
+            dead.join(5)
+            assert not dead.is_alive()
+            assert ready.wait(5), "worker did not install its signal handler"
+            mq = Mock()
+            if cooperative:
+                mq.enqueue.side_effect = lambda *args, **kwargs: stop.set()
+            else:
+                mq.enqueue.side_effect = OSError("shutdown queue unavailable")
+            cleaner = executor_module._ExecutorShutdownCleaner(mq, 2, [dead, worker])
+
+            cleaner()
+
+            assert not worker.is_alive()
+            assert worker.exitcode == (0 if cooperative else -signal.SIGKILL)
+            assert cleaner.processes == []
+            assert cleaner.broadcast_mq is None
+            cleaner()
+        finally:
+            for proc in (dead, worker):
+                if proc.is_alive():
+                    proc.kill()
+                proc.join(5)
+                proc.close()
+
+    @pytest.mark.parametrize("failed_action", ["terminate", "kill"])
+    def test_kill_phase_shares_deadline_and_continues_after_os_errors(self, monkeypatch, failed_action):
+        from vllm_omni.diffusion.executor import multiproc_executor as executor_module
+
+        first, second = Mock(pid=101), Mock(pid=102)
+        first.name, second.name = "first", "second"
+        for proc in (first, second):
+            proc.is_alive.side_effect = [True, True, True, False]
+        getattr(first, failed_action).side_effect = OSError("signal failed")
+        first.join.side_effect = [OSError("join failed"), None, None]
+        monotonic = Mock(side_effect=[100, 100, 110, 120, 120, 124, 130, 130, 134])
+        monkeypatch.setattr(executor_module, "time", SimpleNamespace(monotonic=monotonic))
+        cleaner = executor_module._ExecutorShutdownCleaner(processes=[first, second])
+
+        cleaner()
+
+        first.kill.assert_called_once()
+        second.kill.assert_called_once()
+        assert [call.args[0] for call in first.join.call_args_list] == [15, 5, 5]
+        assert [call.args[0] for call in second.join.call_args_list] == [5, 1, 1]
+        assert cleaner.processes == []
+
+    def test_executor_retains_survivor_for_explicit_shutdown_retry(self, monkeypatch):
+        from vllm_omni.diffusion.executor import multiproc_executor as executor_module
+
+        survivor = Mock(pid=123)
+        survivor.name = "surviving-worker"
+        survivor.is_alive.return_value = True
+        cleaner = executor_module._ExecutorShutdownCleaner(processes=[survivor])
+        executor, _, _ = _make_executor()
+        executor._shutdown_cleaner = cleaner
+        executor._processes = [survivor]
+        executor._finalizer = weakref.finalize(executor, cleaner)
+        executor._pump_stop = threading.Event()
+        executor._futures_lock = threading.RLock()
+        executor._rpc_futures = {}
+        executor._output_futures = {}
+        executor._batch_split_map = {}
+        log_error = Mock()
+        monkeypatch.setattr(executor_module.logger, "error", log_error)
+
+        executor.shutdown()
+
+        assert not executor._finalizer.alive
+        assert executor._shutdown_cleaner is cleaner
+        assert executor._processes == [survivor]
+        log_error.assert_called_once()
+        assert log_error.call_args.args[1] == [("surviving-worker", 123)]
+        survivor.is_alive.return_value = False
+
+        executor.shutdown()
+        executor.shutdown()
+
+        assert executor._shutdown_cleaner is None
+        assert executor._processes == []
+
+    def test_concurrent_cleanup_does_not_repeat_process_operations(self):
+        from vllm_omni.diffusion.executor import multiproc_executor as executor_module
+
+        joining, release = threading.Event(), threading.Event()
+        proc = Mock(pid=123)
+        proc.is_alive.return_value = True
+
+        def join(timeout):
+            joining.set()
+            assert release.wait(5)
+            proc.is_alive.return_value = False
+
+        proc.join.side_effect = join
+        cleaner = executor_module._ExecutorShutdownCleaner(processes=[proc])
+        thread = threading.Thread(target=cleaner)
+        thread.start()
+        try:
+            assert joining.wait(5)
+            cleaner()
+            proc.join.assert_called_once()
+        finally:
+            release.set()
+            thread.join(5)
+        assert not thread.is_alive()
+        assert cleaner.processes == []
+
 
 # ───────── monitor thread & death sentinel integration tests ─────────
 
@@ -1406,7 +1535,7 @@ def test_worker_monitor_sets_is_failed_and_calls_callbacks_on_death(self):
         executor._result_mq = None
         executor._shutdown_cleaner = None
         # Use a no-op so shutdown() doesn't crash on None resources.
-        executor._finalizer = lambda: None
+        executor._finalizer = weakref.finalize(executor, lambda: None)
         # ------------------------------------------------------------------
         # Attributes added by remove_bubble_v2 (async D2H); shutdown() iterates
         # over them, so they need to exist even when constructed via __new__.
@@ -1441,7 +1570,7 @@ def test_worker_monitor_noop_when_already_closed(self):
         executor._broadcast_mq = None
         executor._result_mq = None
         executor._shutdown_cleaner = None
-        executor._finalizer = lambda: None
+        executor._finalizer = weakref.finalize(executor, lambda: None)
 
         proc = _make_short_lived_process()
         executor._processes = [proc]

vllm_omni/diffusion/executor/multiproc_executor.py

@@ -1,3 +1,6 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
 from __future__ import annotations
 
 import concurrent.futures
@@ -10,7 +13,7 @@
 import time
 import weakref
 from collections.abc import Callable
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from multiprocessing.synchronize import Event
 from typing import TYPE_CHECKING, Any, cast
 
@@ -42,6 +45,7 @@
 _DLO_DP_WAVE_TIMEOUT_S = float(os.environ.get("VLLM_OMNI_DLO_DP_WAVE_TIMEOUT", 600.0))
 _WORKER_SHUTDOWN_GRACE_S = 15.0
 _WORKER_TERMINATE_GRACE_S = 5.0
+_WORKER_KILL_GRACE_S = 5.0
 _RESULT_PUMP_JOIN_TIMEOUT_S = 2.0
 
 
@@ -80,33 +84,61 @@ class _ExecutorShutdownCleaner:
     broadcast_mq: MessageQueue | None = None
     num_workers: int = 0
     processes: list[mp.Process] | None = None
+    _lock: threading.Lock = field(default_factory=threading.Lock, init=False, repr=False)
 
     def __call__(self) -> None:
         """Clean up background resources."""
+        # The worker monitor and an explicit shutdown may race. A retry must
+        # not signal/join the same Process objects while cleanup is in flight.
+        if not self._lock.acquire(blocking=False):
+            return
+        try:
+            self._cleanup()
+        finally:
+            self._lock.release()
+
+    def _cleanup(self) -> None:
         if self.broadcast_mq is not None:
             try:
                 for _ in range(self.num_workers):
                     self.broadcast_mq.enqueue(SHUTDOWN_MESSAGE, timeout=1.0)
 
-                self.broadcast_mq = None
             except Exception as exc:
                 logger.warning("Failed to send shutdown signal: %s", exc)
+            finally:
+                self.broadcast_mq = None
 
         if self.processes:
-            join_deadline = time.monotonic() + _WORKER_SHUTDOWN_GRACE_S
-            for proc in self.processes:
-                if not proc.is_alive():
-                    continue
-                proc.join(max(0.0, join_deadline - time.monotonic()))
-
             alive = [proc for proc in self.processes if proc.is_alive()]
-            for proc in alive:
-                logger.warning("Terminating diffusion worker %s after timeout", proc.name)
-                proc.terminate()
+            for action, grace in (
+                (None, _WORKER_SHUTDOWN_GRACE_S),
+                ("terminate", _WORKER_TERMINATE_GRACE_S),
+                ("kill", _WORKER_KILL_GRACE_S),
+            ):
+                if not alive:
+                    break
+                if action is not None:
+                    for proc in alive:
+                        try:
+                            logger.warning("Calling %s on diffusion worker %s (pid=%s)", action, proc.name, proc.pid)
+                            getattr(proc, action)()
+                        except OSError:
+                            logger.exception("Failed to %s diffusion worker %s (pid=%s)", action, proc.name, proc.pid)
 
-            terminate_deadline = time.monotonic() + _WORKER_TERMINATE_GRACE_S
-            for proc in alive:
-                proc.join(max(0.0, terminate_deadline - time.monotonic()))
+                deadline = time.monotonic() + grace
+                for proc in alive:
+                    try:
+                        proc.join(max(0.0, deadline - time.monotonic()))
+                    except OSError:
+                        logger.exception("Failed to join diffusion worker %s (pid=%s)", proc.name, proc.pid)
+                alive = [proc for proc in alive if proc.is_alive()]
+
+            self.processes = alive
+            if alive:
+                logger.error(
+                    "Diffusion worker cleanup incomplete after kill: %s; retaining processes for shutdown retry",
+                    [(proc.name, proc.pid) for proc in alive],
+                )
 
 
 class MultiprocDiffusionExecutor(DiffusionExecutor):
@@ -1006,8 +1038,12 @@ def check_health(self) -> None:
     def shutdown(self) -> None:
         self._closed = True
         self._pump_stop.set()
+        cleaner = self._shutdown_cleaner
         try:
-            self._finalizer()
+            if self._finalizer.alive:
+                self._finalizer()
+            elif cleaner is not None:
+                cleaner()
         finally:
             pump_threads = getattr(self, "_result_pump_threads", [])
             for thread in pump_threads:
@@ -1031,5 +1067,6 @@ def shutdown(self) -> None:
                 self._rpc_futures.clear()
                 self._output_futures.clear()
                 self._batch_split_map.clear()
-            self._shutdown_cleaner = None
-            self._processes = []
+            self._processes = (cleaner.processes or []) if cleaner is not None else []
+            if not self._processes:
+                self._shutdown_cleaner = None