fix(restore,threads): a stopped restore waits for its worker; exit-window thread refusals are quiet (#360, #375) (#404)

* fix(restore): a restore cut off by shutdown waits for its worker thread (#360)

A cancelled restore handler or job no longer removes the stage or the
upload, or ends its exclusive registry admission, while the executor
thread still stages or publishes. The cancel waits for the worker; a
publish that finished is adopted before the cancel goes on, and a stage
finished after the cancel is removed.

* fix(threads): a thread or pool refused at interpreter exit is quiet and leaves nothing pending (#375)

During interpreter exit, threading._shutdown shuts every thread pool
before the package teardown runs while our daemon threads keep working.
map_parallel now runs the items a refused pool did not start on the
calling thread, schedule() drops the path and returns False when its
worker cannot start, and the preview queue skips the file. Each
refusal is logged once at DEBUG without a traceback; other start
failures behave as before.

* fix(restore): keep the cancel and the adoption when a stopped restore's publish ends (#360)

A publish that fails after the cancel now ends in CancelledError (after
its prune) instead of a 500, and the restored library is adopted to its
end even when a second cancel arrives. The blocking calls go through
_run_in_executor again, as the executor contract test expects.

Exit-window refusals: the comments state what was measured (a pool is
refused during threading._shutdown; Thread.start only once the
interpreter is finalizing), and the tests assert the one DEBUG line.

py/api/backup_restore.py

@@ -483,13 +483,59 @@ class BackupRestoreRoutesMixin:
             self.logger.info(f"Removed {len(removed)} old safety backups")
 
     async def _publish(self, model, staged):
-        """Publish ``staged``; on a page-copy failure prune and re-raise."""
+        """Publish ``staged``; on a page-copy failure prune and re-raise.
+
+        A cancel (server stop) waits for the publishing thread (#360): the
+        caller's cleanup and its registry admission must outlive it. When the
+        copy then succeeded the library was replaced, so it is adopted
+        (``_after_publish``, itself run to its end) before the cancel goes
+        on; a copy that failed is handled as usual, then the cancel goes on.
+        """
+        future = self._in_executor_task(model.publish_staged, staged)
+        cancelled = await _outlive_cancel(future)
         try:
-            return await self._run_in_executor(model.publish_staged, staged)
+            backup_path = future.result()
         except sqlite3.OperationalError as exc:
             if getattr(exc, "_prompt_manager_restore_backup_created", False) is True:
                 await self._prune_after(model.db_path, failed=True)
+            if cancelled:
+                raise asyncio.CancelledError from exc
             raise
+        except Exception as exc:
+            if cancelled:
+                raise asyncio.CancelledError from exc
+            raise
+        if cancelled:
+            self.logger.info("The restore finished while the server was stopping")
+            # A second cancel (the loop's own shutdown) must not cut it short.
+            adopted = asyncio.ensure_future(self._after_publish(model.db_path))
+            await _outlive_cancel(adopted)
+            if not adopted.cancelled() and adopted.exception() is not None:
+                self.logger.error(
+                    "Could not adopt the restored library",
+                    exc_info=adopted.exception(),
+                )
+            raise asyncio.CancelledError
+        return backup_path
+
+    async def _stage_to_end(self, model, temp_path):
+        """Stage ``temp_path``; a cancel waits for the worker (#360).
+
+        The upload stays until the staging thread is done with it, and a
+        stage it finished after the cancel is removed before the cancel goes
+        on.
+        """
+        future = self._in_executor_task(model.stage_restore, temp_path)
+        if await _outlive_cancel(future):
+            if not future.cancelled() and future.exception() is None:
+                await self._discard_held([_Orphan(future.result())])
+            raise asyncio.CancelledError
+        return future.result()
+
+    def _in_executor_task(self, func, *args):
+        """``_run_in_executor(func, *args)`` as a task ``_outlive_cancel`` can
+        wait for (shielded, the executor call is never cancelled)."""
+        return asyncio.ensure_future(self._run_in_executor(func, *args))
 
     async def _after_publish(self, db_path):
         """Everything after the copy replaced the library: best effort, logged.
@@ -609,7 +655,7 @@ class BackupRestoreRoutesMixin:
                     {"success": False, "error": REQUESTS_BUSY}, status=409
                 )
             model = self.db.model
-            staged = await self._run_in_executor(model.stage_restore, temp_path)
+            staged = await self._stage_to_end(model, temp_path)
             try:
                 backup_path = await self._publish(model, staged)
             finally:
@@ -927,6 +973,30 @@ class BackupRestoreRoutesMixin:
         job.update(progress=100, status_line=line)
 
 
+async def _outlive_cancel(future):
+    """Await ``future`` (an executor call's task) to its end, even through
+    cancels (#360).
+
+    A cancelled task cannot stop the worker thread, so the files it uses and
+    the registry admission it runs under must outlive it: the cancel is held
+    until the worker returned. Returns whether the task was cancelled
+    meanwhile; the caller reads the outcome from ``future`` and re-raises
+    ``CancelledError``. A future cancelled itself (an executor shut down) is
+    not a cancel of the task: ``future.result()`` raises it. Never catches
+    ``GeneratorExit``: a closed loop still closes the coroutine.
+    """
+    cancelled = False
+    while not future.done():
+        try:
+            await asyncio.shield(future)
+        except asyncio.CancelledError:
+            if not future.cancelled():
+                cancelled = True
+        except Exception:
+            pass  # the caller reads it from the future
+    return cancelled
+
+
 class _Orphan:
     """A stage with no store entry, in the shape ``_discard_held`` takes."""
 

py/api/thumbnail_auto.py

@@ -88,9 +88,9 @@ from .thumbnail_encode import shutdown_encoders, writer_settings
 from .thumbnail_jobs import ThumbnailOptions
 
 try:
-    from ...utils.parallel import map_parallel
+    from ...utils.parallel import map_parallel, note_refusal, refused_at_shutdown
 except ImportError:  # tests import the package top-level
-    from utils.parallel import map_parallel
+    from utils.parallel import map_parallel, note_refusal, refused_at_shutdown
 
 # The placeholder frame a video without a preview is answered with (JPEG
 # bytes, never written to disk); written previews follow the settings.
@@ -410,7 +410,8 @@ class AutoThumbnailer:
 
     def enqueue(self, src, dst, is_video):
         """Queue *dst*'s preview for the worker; False when already queued,
-        full or closed. Never blocks on a write."""
+        full, closed or its worker is refused at interpreter exit. Never
+        blocks on a write."""
         key = _dst_key(dst)
         with self._changed:
             if self._closed or key in self._queued:
@@ -420,30 +421,41 @@ class AutoThumbnailer:
             self._queued.add(key)
             self._queue.append((key, Path(src), Path(dst), bool(is_video)))
             self._busy = True
+            started = True
             if self._start_worker and not self._worker_running:
-                self._start_worker_locked()
+                started = self._start_worker_locked()
+            if not started:
+                # Refused at interpreter exit: no worker will take it (#375).
+                self._queue.pop()
+                self._queued.discard(key)
             self._changed.notify_all()
-        return True
+        return started
 
     def _start_worker_locked(self):
-        """Start the worker (lock held). A start that fails leaves the file
-        queued and the next enqueue tries again."""
+        """Start the worker (lock held); False only when the interpreter is
+        exiting (#375: logged once at DEBUG, the caller drops the file).
+        Another start failure leaves the file queued and the next enqueue
+        tries again."""
         worker = threading.Thread(target=self._run, name=WORKER_NAME, daemon=True)
         worker.pm_preview_token = _MODULE_TOKEN
         worker.pm_preview_close = self.close
         self._worker_running = True
         try:
             worker.start()
-        except RuntimeError:
+        except RuntimeError as error:
             self._worker_running = False
             self._busy = False
+            if refused_at_shutdown(error):
+                note_refusal(self._logger, "The automatic preview worker")
+                return False
             self._logger.warning(
                 "The automatic preview worker could not start; the next output "
                 "tries again",
                 exc_info=True,
             )
-            return
+            return True
         self._worker = worker
+        return True
 
     def _run(self):
         try:
@@ -790,8 +802,8 @@ class AutoThumbnailMixin:
 
         Returns ``queued``, ``fresh`` (its preview is current) or ``skipped``
         (not a media file under a current root, a link, a preview itself,
-        already queued, or after the app's cleanup). Never writes on the
-        caller's thread.
+        already queued, after the app's cleanup, or when its worker is refused
+        at interpreter exit). Never writes on the caller's thread.
         """
         if self._auto_thumbnails_shut:
             return "skipped"

tests/test_exit_window_threads.py

@@ -0,0 +1,266 @@
+"""A thread or pool refused at interpreter shutdown is quiet (#375).
+
+When the interpreter exits, ``threading._shutdown`` first shuts every
+``ThreadPoolExecutor`` (``submit`` then raises "cannot schedule new futures
+after interpreter shutdown") and joins the non-daemon threads; only then do
+the ``atexit`` callbacks (the package teardown) run. Our daemon threads keep
+working meanwhile. ``Thread.start`` is refused ("can't create new thread at
+interpreter shutdown") only later, once the interpreter is finalizing; the
+unit tests cover that case, the child process the pool case. Such a refusal
+is logged once at DEBUG, with no traceback, and leaves nothing pending.
+
+``threading.Thread`` is replaced only in the module under test (a copy of
+the ``threading`` namespace), never process-wide. The child-process test runs
+the real exit: a daemon thread queues previews while the main thread returns.
+"""
+
+import json
+import logging
+import os
+import subprocess
+import sys
+import tempfile
+import textwrap
+import threading
+import types
+import unittest
+from concurrent.futures import ThreadPoolExecutor
+from pathlib import Path
+from unittest import mock
+
+from py.api import thumbnail_auto
+from utils import image_monitor, parallel
+
+ROOT = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+CHILD_CEILING_SECONDS = 60  # the hang watchdog allows 120 s per test
+REPORT_PREFIX = "PM_EXIT_REPORT "
+THREAD_REFUSAL = "can't create new thread at interpreter shutdown"
+POOL_REFUSAL = "cannot schedule new futures after interpreter shutdown"
+
+
+def _refusing_threading():
+    """A ``threading`` namespace whose ``Thread.start`` is refused."""
+
+    class RefusedThread(threading.Thread):
+        def start(self):
+            raise RuntimeError(THREAD_REFUSAL)
+
+    namespace = types.SimpleNamespace(**vars(threading))
+    namespace.Thread = RefusedThread
+    return namespace
+
+
+class _ShutPool(ThreadPoolExecutor):
+    def submit(self, *args, **kwargs):
+        raise RuntimeError(POOL_REFUSAL)
+
+
+class _Capture(logging.Handler):
+    def __init__(self):
+        super().__init__(logging.DEBUG)
+        self.records = []
+
+    def emit(self, record):
+        self.records.append(record)
+
+
+def _capture(testcase, name):
+    parallel._noted.clear()  # "once" is per process: start each test afresh
+    logger = logging.getLogger(name)
+    handler = _Capture()
+    previous = logger.level
+    logger.addHandler(handler)
+    logger.setLevel(logging.DEBUG)
+
+    def restore():
+        logger.removeHandler(handler)
+        logger.setLevel(previous)
+
+    testcase.addCleanup(restore)
+    return handler.records
+
+
+def _assert_one_debug_line(testcase, records):
+    """Exactly one refusal line, at DEBUG and without a traceback."""
+    refusals = [r for r in records if "interpreter is exiting" in r.getMessage()]
+    testcase.assertEqual(len(refusals), 1, [r.getMessage() for r in records])
+    testcase.assertEqual(refusals[0].levelno, logging.DEBUG)
+    testcase.assertEqual([r for r in records if r.levelno > logging.DEBUG], [])
+    testcase.assertTrue(all(r.exc_info is None for r in records))
+
+
+class TestScheduleRefusedAtShutdown(unittest.TestCase):
+    def setUp(self):
+        self.handler = image_monitor.ImageGenerationHandler(
+            mock.MagicMock(), mock.MagicMock()
+        )
+        self.addCleanup(self.handler.close)
+
+    def test_schedule_returns_false_and_leaves_nothing_pending(self):
+        records = _capture(self, "prompt_manager.image_monitor")
+        with mock.patch.object(image_monitor, "threading", _refusing_threading()):
+            self.assertFalse(self.handler.schedule("/out/a.png"))
+            self.assertFalse(self.handler.schedule("/out/b.png"))
+        self.assertEqual(self.handler.pending_count(), 0)
+        _assert_one_debug_line(self, records)
+
+    def test_another_start_failure_still_raises_and_leaves_nothing_pending(self):
+        class Failing(threading.Thread):
+            def start(self):
+                raise RuntimeError("can't start new thread")
+
+        namespace = types.SimpleNamespace(**vars(threading))
+        namespace.Thread = Failing
+        with mock.patch.object(image_monitor, "threading", namespace):
+            with self.assertRaises(RuntimeError):
+                self.handler.schedule("/out/a.png")
+        self.assertEqual(self.handler.pending_count(), 0)
+
+    def test_schedule_before_shutdown_is_unchanged(self):
+        self.handler.processing_delay = 3600
+        self.assertTrue(self.handler.schedule("/out/a.png"))
+        self.assertEqual(self.handler.pending_count(), 1)
+
+
+class TestPreviewQueueRefusedAtShutdown(unittest.TestCase):
+    def thumbnailer(self, logger):
+        made = thumbnail_auto.AutoThumbnailer(
+            lambda *a, **k: {"action": "generated"}, lambda: True, logger
+        )
+        self.addCleanup(made.close)
+        return made
+
+    def test_enqueue_is_refused_quietly_and_drops_the_file(self):
+        logger = logging.getLogger("prompt_manager.test_exit_window")
+        records = _capture(self, logger.name)
+        thumbnailer = self.thumbnailer(logger)
+        src = Path("/out/a.png")
+        with mock.patch.object(thumbnail_auto, "threading", _refusing_threading()):
+            self.assertFalse(thumbnailer.enqueue(src, Path("/out/t/a.webp"), False))
+            self.assertFalse(thumbnailer.enqueue(src, Path("/out/t/b.webp"), False))
+        self.assertFalse(thumbnailer._worker_running)
+        self.assertEqual(len(thumbnailer._queue), 0)
+        self.assertEqual(thumbnailer._queued, set())
+        self.assertTrue(thumbnailer.wait_idle(0))
+        _assert_one_debug_line(self, records)
+
+
+class TestMapParallelRefusedAtShutdown(unittest.TestCase):
+    def test_a_shut_pool_runs_the_items_on_the_calling_thread(self):
+        records = _capture(self, "prompt_manager.parallel")
+        with mock.patch.object(parallel, "ThreadPoolExecutor", _ShutPool):
+            self.assertEqual(
+                parallel.map_parallel(lambda n: n * n, [1, 2, 3], 4), [1, 4, 9]
+            )
+        _assert_one_debug_line(self, records)
+
+    def test_another_pool_error_still_raises(self):
+        class Broken(ThreadPoolExecutor):
+            def submit(self, *args, **kwargs):
+                raise RuntimeError("something else")
+
+        with mock.patch.object(parallel, "ThreadPoolExecutor", Broken):
+            with self.assertRaises(RuntimeError):
+                parallel.map_parallel(lambda n: n, [1, 2], 2)
+
+
+CHILD = textwrap.dedent("""
+    import threading
+
+    # Registered before concurrent.futures is imported, so it runs after the
+    # pool's own exit hook: from here on, a pool refuses new work.
+    exiting = threading.Event()
+    threading._register_atexit(exiting.set)
+
+    import json
+    import logging
+    import os
+    import sys
+    from pathlib import Path
+
+    root, tmp = sys.argv[1], sys.argv[2]
+    sys.path.insert(0, root)
+
+    from py.api.thumbnail_auto import AutoThumbnailer
+
+    logging.basicConfig(level=logging.WARNING, stream=sys.stderr)
+    logger = logging.getLogger("prompt_manager.exit_child")
+
+    def generate(src, dst, is_video, *, stop, guard, track):
+        Path(dst).write_bytes(b"preview")
+        return {"action": "generated"}
+
+    thumbnailer = AutoThumbnailer(
+        generate, lambda: True, logger, workers=lambda: 4
+    )
+    queued = threading.Event()
+
+    def late_monitor():
+        exiting.wait()
+        # One batch of two: the worker maps it on a pool.
+        with thumbnailer._changed:
+            for name in ("a", "b"):
+                src = Path(tmp, name + ".png")
+                src.write_bytes(b"x")
+                thumbnailer.enqueue(src, Path(tmp, name + "_thumb.webp"), False)
+        queued.set()
+
+    def holder():
+        # Non-daemon: the interpreter waits for it, inside the exit window.
+        exiting.wait()
+        queued.wait(30)
+        idle = thumbnailer.wait_idle(30)
+        written = sorted(
+            n for n in os.listdir(tmp) if n.endswith("_thumb.webp")
+        )
+        print("PM_EXIT_REPORT " + json.dumps({"idle": idle, "written": written}))
+        sys.stdout.flush()
+
+    threading.Thread(target=late_monitor, daemon=True).start()
+    threading.Thread(target=holder).start()
+    # Return normally, as ComfyUI does after Ctrl+C.
+    """)
+
+
+class TestExitWindowChild(unittest.TestCase):
+    def test_previews_queued_in_the_exit_window_log_no_traceback(self):
+        with tempfile.TemporaryDirectory() as tmp:
+            script = os.path.join(tmp, "child.py")
+            with open(script, "w", encoding="utf-8") as handle:
+                handle.write(CHILD)
+            env = dict(os.environ)
+            env.pop("PROMPT_MANAGER_CONFIG_PATH", None)
+            env["PROMPT_MANAGER_DATA_DIR"] = tmp
+            env["PYTHONIOENCODING"] = "utf-8"
+            try:
+                completed = subprocess.run(
+                    [sys.executable, script, ROOT, tmp],
+                    cwd=ROOT,
+                    env=env,
+                    capture_output=True,
+                    timeout=CHILD_CEILING_SECONDS,
+                    encoding="utf-8",
+                    errors="replace",
+                )
+            except subprocess.TimeoutExpired as hung:
+                self.fail(
+                    f"the child did not exit within {CHILD_CEILING_SECONDS} s\n"
+                    f"stdout:\n{hung.stdout}\nstderr:\n{hung.stderr}"
+                )
+        detail = f"stdout:\n{completed.stdout}\nstderr:\n{completed.stderr}"
+        self.assertEqual(completed.returncode, 0, detail)
+        reports = [
+            line[len(REPORT_PREFIX) :]
+            for line in completed.stdout.splitlines()
+            if line.startswith(REPORT_PREFIX)
+        ]
+        self.assertEqual(len(reports), 1, detail)
+        report = json.loads(reports[0])
+        self.assertTrue(report["idle"], detail)
+        # The batch still ran: on the worker's own thread.
+        self.assertEqual(report["written"], ["a_thumb.webp", "b_thumb.webp"], detail)
+        self.assertNotIn("Traceback", completed.stderr, detail)
+
+
+if __name__ == "__main__":
+    unittest.main()

tests/test_restore_shutdown.py

@@ -0,0 +1,233 @@
+"""A restore cut off by a server stop waits for its worker thread (#360).
+
+A cancelled handler (or job) task cannot stop the executor thread that
+stages or publishes. Its cleanup (the stage, the upload) and the registry's
+``restore`` admission must outlive that thread, and the live library ends as
+the old or the restored one, never partial, with the safety backup kept.
+
+Every positive wait is on an event. The one bounded wait (``SETTLE``) is a
+negative check: the cancelled task must still be pending while its worker is
+held.
+"""
+
+import asyncio
+import os
+import shutil
+import sqlite3
+import threading
+from unittest.mock import patch
+
+from database import restore_stage
+from database.models import PromptModel
+from py.api import admin as admin_mod
+from py.api.jobs import RESTORE_JOB_KIND
+
+try:
+    from tests.test_restore_plans import RestoreTestCase, _texts
+except ImportError:  # discovered with tests/ as the top-level directory
+    from test_restore_plans import RestoreTestCase, _texts
+
+WAIT = 60  # a ceiling only a hung test reaches
+SETTLE = 0.3  # the negative check's bound: the old code's cleanup takes ms
+
+
+class _Gate:
+    """Hold one blocking call on its worker thread until released."""
+
+    def __init__(self, real):
+        self.real = real
+        self.entered = threading.Event()
+        self.release = threading.Event()
+        self.done = threading.Event()
+
+    def method(self):
+        """A function to patch onto the class (bound like the real one)."""
+
+        def held(*args):
+            return self(*args)
+
+        return held
+
+    def __call__(self, *args):
+        self.entered.set()
+        self.release.wait(WAIT)
+        try:
+            return self.real(*args)
+        finally:
+            self.done.set()
+
+
+class ShutdownRestoreCase(RestoreTestCase):
+    def gate(self, real):
+        gate = _Gate(real)
+        # A failed check never leaves the worker held until WAIT.
+        self._gates = getattr(self, "_gates", []) + [gate]
+        self.addCleanup(gate.release.set)
+        return gate
+
+    def stages(self):
+        """The stage folders (the upload's prefix starts the same way)."""
+        return [
+            name
+            for name in super().stages()
+            if os.path.isdir(os.path.join(self.tmpdir, name))
+        ]
+
+    def uploads(self):
+        """The upload files (not the -wal/-shm its readers may add)."""
+        return sorted(
+            name
+            for name in os.listdir(self.tmpdir)
+            if name.startswith(restore_stage.UPLOAD_PREFIX) and name.endswith(".tmp")
+        )
+
+    def fake_upload(self, texts):
+        """Make ``_receive_restore_upload`` hand over a prepared upload."""
+        self.upload(texts, "source.db")
+        source = os.path.join(self.tmpdir, "uploads", "source.db")
+        target = os.path.join(self.tmpdir, restore_stage.UPLOAD_PREFIX + "x.tmp")
+        shutil.copyfile(source, target)
+
+        async def receive(request, uploads):
+            uploads.append(target)
+            return target, None
+
+        return patch.object(self.api, "_receive_restore_upload", receive)
+
+    async def wait_thread(self, event):
+        loop = asyncio.get_running_loop()
+        self.assertTrue(await loop.run_in_executor(None, event.wait, WAIT))
+
+    async def assert_still_pending(self, task):
+        done, _ = await asyncio.wait({task}, timeout=SETTLE)
+        if done:
+            for gate in getattr(self, "_gates", ()):
+                gate.release.set()  # let the worker end before teardown
+            self.fail("the cancelled task ended while its worker still ran")
+
+
+class TestLegacyRestoreAtShutdown(ShutdownRestoreCase):
+    async def test_cancel_during_publish_waits_for_the_worker(self):
+        self.save("old")
+        old_db = self.api.db
+        gate = self.gate(PromptModel.publish_staged)
+        with (
+            self.fake_upload(["restored"]),
+            patch.object(PromptModel, "publish_staged", gate.method()),
+        ):
+            task = asyncio.ensure_future(self.api.restore_database(None))
+            await self.wait_thread(gate.entered)
+            self.assertEqual(len(self.stages()), 1)
+            task.cancel()
+            await self.assert_still_pending(task)
+            # The worker still has its stage and upload, and runs alone.
+            self.assertEqual(len(self.stages()), 1)
+            self.assertEqual(len(self.uploads()), 1)
+            self.assertIsNotNone(self.api._jobs.active(RESTORE_JOB_KIND))
+            gate.release.set()
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.wait_for(task, WAIT)
+        self.assertTrue(gate.done.is_set())
+        self.assertEqual(_texts(self.db_path), ["restored"])
+        self.assertIsNot(self.api.db, old_db)  # the restored library adopted
+        self.assertEqual(len(self.backups()), 1)  # the safety backup is kept
+        self.assertEqual(self.stages(), [])
+        self.assertEqual(self.uploads(), [])
+        self.assertIsNone(self.api._jobs.active(RESTORE_JOB_KIND))
+
+    async def test_cancel_during_staging_waits_and_changes_nothing(self):
+        self.save("old")
+        gate = self.gate(PromptModel.stage_restore)
+        with (
+            self.fake_upload(["restored"]),
+            patch.object(PromptModel, "stage_restore", gate.method()),
+        ):
+            task = asyncio.ensure_future(self.api.restore_database(None))
+            await self.wait_thread(gate.entered)
+            task.cancel()
+            await self.assert_still_pending(task)
+            self.assertEqual(len(self.uploads()), 1)  # still being read
+            self.assertIsNotNone(self.api._jobs.active(RESTORE_JOB_KIND))
+            gate.release.set()
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.wait_for(task, WAIT)
+        self.assertEqual(_texts(self.db_path), ["old"])
+        self.assertEqual(self.backups(), [])
+        self.assertEqual(self.stages(), [])  # the finished stage is removed
+        self.assertEqual(self.uploads(), [])
+        self.assertIsNone(self.api._jobs.active(RESTORE_JOB_KIND))
+
+    async def test_a_publish_that_fails_after_the_cancel_still_cancels(self):
+        self.save("old")
+
+        def refuse(model, staged):
+            raise sqlite3.OperationalError("refused")
+
+        gate = self.gate(refuse)
+        with (
+            self.fake_upload(["restored"]),
+            patch.object(PromptModel, "publish_staged", gate.method()),
+        ):
+            task = asyncio.ensure_future(self.api.restore_database(None))
+            await self.wait_thread(gate.entered)
+            task.cancel()
+            await self.assert_still_pending(task)
+            gate.release.set()
+            # Not answered as a 500: the cancel goes on.
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.wait_for(task, WAIT)
+        self.assertEqual(_texts(self.db_path), ["old"])
+        self.assertEqual(self.stages(), [])
+        self.assertEqual(self.uploads(), [])
+        self.assertIsNone(self.api._jobs.active(RESTORE_JOB_KIND))
+
+    async def test_a_second_cancel_still_adopts_the_restored_library(self):
+        self.save("old")
+        old_db = self.api.db
+        publish = self.gate(PromptModel.publish_staged)
+        prune = self.gate(admin_mod._prune_safety_backups)
+        with (
+            self.fake_upload(["restored"]),
+            patch.object(PromptModel, "publish_staged", publish.method()),
+            patch.object(admin_mod, "_prune_safety_backups", prune),
+        ):
+            task = asyncio.ensure_future(self.api.restore_database(None))
+            await self.wait_thread(publish.entered)
+            task.cancel()
+            await self.assert_still_pending(task)
+            publish.release.set()
+            await self.wait_thread(prune.entered)  # adopting the library
+            task.cancel()  # the loop's own shutdown cancels again
+            await self.assert_still_pending(task)
+            prune.release.set()
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.wait_for(task, WAIT)
+        self.assertEqual(_texts(self.db_path), ["restored"])
+        self.assertIsNot(self.api.db, old_db)
+        self.assertEqual(len(self.backups()), 1)
+        self.assertEqual(self.stages(), [])
+        self.assertIsNone(self.api._jobs.active(RESTORE_JOB_KIND))
+
+
+class TestReviewedRestoreAtShutdown(ShutdownRestoreCase):
+    async def test_cancelled_job_waits_for_the_publish(self):
+        self.save("old")
+        old_db = self.api.db
+        body = await self.preview(self.upload(["restored"]))
+        gate = self.gate(PromptModel.publish_staged)
+        with patch.object(PromptModel, "publish_staged", gate.method()):
+            started = await self.apply(body["token"])
+            job = self.api._jobs.get(started["job"]["id"])
+            await self.wait_thread(gate.entered)
+            job.task.cancel()
+            await self.assert_still_pending(job.task)
+            self.assertEqual(len(self.stages()), 1)
+            self.assertTrue(job.running)  # its exclusive admission holds
+            gate.release.set()
+            with self.assertRaises(asyncio.CancelledError):
+                await asyncio.wait_for(job.task, WAIT)
+        self.assertEqual(_texts(self.db_path), ["restored"])
+        self.assertIsNot(self.api.db, old_db)
+        self.assertEqual(len(self.backups()), 1)
+        self.assertEqual(self.stages(), [])
+        self.assertFalse(job.running)

tests/test_thumbnail_auto.py

@@ -978,6 +978,27 @@ class TestThumbnailOnCapture(AutoThumbnailCase):
                 (self.output_dir / "thumbnails" / f"{name}_thumb.webp").is_file()
             )
 
+    async def test_a_worker_refused_at_interpreter_exit_skips_quietly(self):
+        """#375: refused once the interpreter exits; nothing stays queued."""
+
+        class Refused(threading.Thread):
+            def start(self):
+                raise RuntimeError("can't create new thread at interpreter shutdown")
+
+        namespace = type(sys)("threading_copy")
+        namespace.__dict__.update(vars(threading))
+        namespace.Thread = Refused
+        thumbnailer = self.api._auto_thumbnails()
+        path = make_png(self.output_dir / "late.png", size=(32, 32))
+        with (
+            patch.object(auto, "threading", namespace),
+            self.assertNoLogs("prompt_manager.api", "INFO"),
+        ):
+            self.assertEqual(self.api.queue_capture_thumbnail(str(path)), "skipped")
+        self.assertFalse(thumbnailer._worker_running)
+        self.assertEqual(len(thumbnailer._queue), 0)
+        self.assertTrue(thumbnailer.wait_idle(0))
+
     def test_queue_is_bounded(self):
         thumbnailer = auto.AutoThumbnailer(
             lambda *a: {"action": "generated"},

utils/image_monitor.py

@@ -35,6 +35,7 @@ from watchdog.events import FileSystemEventHandler
 
 from .hashing import generate_prompt_hash
 from .metadata_extractor import ComfyUIMetadataExtractor
+from .parallel import note_refusal, refused_at_shutdown
 from .logging_config import get_logger
 from .prompt_graph import resolve_text, run_prompt_nodes
 from .prompt_pair_resolver import resolve_prompt_pair
@@ -194,8 +195,9 @@ class ImageGenerationHandler(FileSystemEventHandler):
         and once its size has stopped changing.
 
         Returns:
-            False when the path is already pending, the pending set is full or
-            the handler is closed
+            False when the path is already pending, the pending set is full,
+            the handler is closed or the interpreter is exiting (its worker
+            cannot start)
         """
         with self._pending_lock:
             if self._closed:
@@ -211,7 +213,15 @@ class ImageGenerationHandler(FileSystemEventHandler):
                 return False
             due = time.monotonic() + self.processing_delay
             self._pending[image_path] = (prompt_snapshot, due)
-            self._ensure_worker()
+            try:
+                self._ensure_worker()
+            except RuntimeError as error:
+                # No worker will ever take it: never leave it pending (#375).
+                self._pending.pop(image_path, None)
+                if not refused_at_shutdown(error):
+                    raise
+                note_refusal(self.logger, "The image worker")
+                return False
             self._work.put(image_path)
         return True
 

utils/parallel.py

@@ -5,17 +5,51 @@ a CUDA-initialised, multi-threaded process is unsafe and the spawn start
 method would re-import ComfyUI's main module in every child. Pillow releases
 the GIL while decoding, resizing and encoding, so threads still scale close
 to linearly for both jobs.
+
+Interpreter exit (#375): ``threading._shutdown`` shuts every thread pool
+(``submit`` then raises "cannot schedule new futures after interpreter
+shutdown") before it joins the non-daemon threads and long before the package
+teardown runs, while our daemon threads keep working. Measured on 3.12 and
+3.14, ``Thread.start`` still succeeds in that window; it is refused ("can't
+create new thread at interpreter shutdown") only once the interpreter is
+marked finalizing, after the ``atexit`` callbacks. ``refused_at_shutdown``
+recognises both; ``note_refusal`` logs one DEBUG line per place, with no
+traceback.
 """
 
+import logging
+import threading
 from concurrent.futures import ThreadPoolExecutor
 
+SHUTDOWN_REFUSAL = "interpreter shutdown"
+_logger = logging.getLogger("prompt_manager.parallel")
+_noted = set()
+_noted_lock = threading.Lock()
+
+
+def refused_at_shutdown(error):
+    """Whether ``error`` is a thread or pool start refused at interpreter exit."""
+    return isinstance(error, RuntimeError) and SHUTDOWN_REFUSAL in str(error)
+
+
+def note_refusal(logger, what):
+    """Log once per ``what``, at DEBUG and without a traceback, that ``what``
+    was refused because the interpreter is exiting."""
+    key = (logger.name, what)
+    with _noted_lock:
+        if key in _noted:
+            return
+        _noted.add(key)
+    logger.debug(f"{what}: refused, the interpreter is exiting")
+
 
 def map_parallel(func, items, workers):
     """Apply ``func`` to every item on up to ``workers`` threads, keeping order.
 
     ``workers`` of 1 (or fewer) runs on the calling thread with no pool. An
     exception in ``func`` propagates to the caller, so callers that must
-    survive bad input wrap ``func`` themselves.
+    survive bad input wrap ``func`` themselves. A pool refused at interpreter
+    exit runs the items it did not start on the calling thread (#375).
     """
     items = list(items)
     workers = max(1, int(workers or 1))
@@ -23,4 +57,35 @@ def map_parallel(func, items, workers):
         return [func(item) for item in items]
     max_workers = min(workers, len(items))
     with ThreadPoolExecutor(max_workers, thread_name_prefix="pm-worker") as pool:
-        return list(pool.map(func, items))
+        futures = []
+        try:
+            for item in items:
+                futures.append(pool.submit(func, item))
+        except RuntimeError as error:
+            if not refused_at_shutdown(error):
+                raise
+            note_refusal(_logger, "A worker pool")
+            # Drop what was queued but not started; it runs here instead.
+            # (A refused Thread.start leaves its item queued without a future
+            # here: it is cancelled too, unless a busy pool thread took it in
+            # between, the one case where an item can run twice.)
+            pool.shutdown(wait=True, cancel_futures=True)
+        else:
+            return [future.result() for future in futures]
+    return _run_rest(func, items, futures)
+
+
+def _run_rest(func, items, futures):
+    """The pool's finished results, and every item it did not run, run here.
+
+    After ``shutdown(cancel_futures=True)`` each submitted future either ran
+    (its result or exception is kept) or was cancelled before it started.
+    """
+    results = []
+    for index, item in enumerate(items):
+        future = futures[index] if index < len(futures) else None
+        if future is not None and not future.cancelled():
+            results.append(future.result())
+        else:
+            results.append(func(item))
+    return results