Fix worker shutdown hanging on side tasks that ignore cancellation - #1616
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Worker._shutdown cancelled its side tasks then awaited them unbounded. A cancellation can be lost when it lands as the task takes its first step: the task keeps looping and, since a side task only wakes on its own schedule, the gather waits for it for ever. Observed with the periodic deferrer, whose sleep runs to the next cron tick, but the heartbeat and abort-polling tasks have the same shape. This is reachable from any cancellation-based shutdown, including the documented asyncio.wait_for(app.run_worker_async(), timeout=...): run() turns a cancellation into a graceful stop, so the hanging gather blocks it for good. Re-cancel while tasks are still pending; the second cancellation lands on an ordinary sleep and takes effect. Give up after CANCEL_ATTEMPTS rather than hanging, and log instead of raising: _shutdown runs in the run loop's finally, so raising would mask whatever caused the shutdown and would turn a cancelled worker into an error rather than a CancelledError. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
test_procrastinate_periodic_defers ran the worker for a fixed 0.1 s and then indexed the resulting row, so a runner too slow to finish worker startup in that window failed with IndexError rather than a useful message. Run the worker until the deferrer has actually written its row. This needs the side task cancellation fix from the previous commit: cancelling once the row lands means cancelling during startup, which is exactly when the deferrer's cancellation could be lost. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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Included review availability: Your plan provides up to 4 included reviews per hour; 0 remain after this review. 📝 WalkthroughWalkthroughThe change adds bounded cancellation retries and timeout handling to ChangesCancellation shutdown handling
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: 🟡 Moderate · up to The PR fixes worker shutdown hangs and adds regression coverage, but an integration test still relies on asynchronous QuerySet iteration that is unavailable with the supported Django 2.2.0 dependency. The PR is not merge-ready until that test is made compatible or the limitation is explicitly accepted. Suggested reviewers: 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
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In `@procrastinate/utils.py`:
- Around line 253-266: The cancellation-failure branch must log exceptions from
completed tasks before abandoning pending ones. Before the return in the else
branch, iterate over tasks that are done and not cancelled, and pass each to the
existing log_task_exception flow; do not await or otherwise block on tasks that
remain stuck.
- Around line 247-266: Ensure the task-shutdown logic around the final
task.cancel() gives pending tasks one last timed wait to process cancellation
before entering the for-else abandonment path. Preserve the existing
cancellation limit and logging behavior, and add a regression test covering a
task that stops only after the final permitted cancellation.
In `@tests/integration/contrib/django/test_models.py`:
- Around line 118-122: Update list_periodic_defers to avoid asynchronous
QuerySet iteration on Django 2.2 by wrapping the synchronous values().all()
query with the existing asgiref.sync.sync_to_async bridge, preserving the
helper’s asynchronous interface and returned records.
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Two review findings on the cancellation loop: The initial cancellation sat outside the loop, so the last cancellation the loop sent was never waited on. Reaping was unaffected (that cancellation was beyond the budget either way) but it made CANCEL_ATTEMPTS mean "N waits and N+1 cancellations". Cancel at the top of each round instead, so the constant means N cancel-and-wait rounds and no cancellation goes unwaited. Giving up returned before errors were captured, so one task refusing to stop discarded another task's exception, which was then never retrieved. Capture the errors of the tasks that did stop before abandoning the rest. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
The test cancelled the worker and awaited it with no bound, so a worker that refused to shut down would hang the job rather than fail the test. That is worth avoiding in a test whose whole point is a shutdown that used to hang: a hung job holds a runner until CI's own timeout and, with the matrix cancelling siblings, reports as several versions failing for no visible reason. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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The bug
Worker._shutdowncancels its side tasks and then awaits them with no bound, atutils.cancel_and_capture_errors:A cancellation can be lost when it lands just as the task takes its first step.
Tracing the periodic deferrer's own methods at the moment of the hang:
The task reports
cancelling=1while parked on a fresh, uncancelled future insideasyncio.sleep, so thegatherwaits for a task that only wakes on its own cronschedule — and once awake it just loops and sleeps again.
It hangs permanently, not until the next tick. 3 of 12 runs were still stuck after
120 s despite a ~30 s sleep.
Two things make this worse than it looks:
asyncio.wait_for(app.run_worker_async(), timeout=...).Worker.rundeliberatelyconverts a cancellation into a graceful stop (shield the loop, then
stop()+await loop_task), so the hanging gather blocks that path for good.while True: await asyncio.sleep(...)shape —
_update_heartbeatand_poll_jobs_to_abortas well as the deferrer. Thedeferrer merely has the longest sleep, so it is the one that shows up. The fix is
therefore generic rather than deferrer-specific.
The fix
Re-cancel while tasks are still pending. The second cancellation lands on an ordinary
asyncio.sleepand takes effect. AfterCANCEL_ATTEMPTS(5 × 1 s) it gives up andlogs rather than hanging.
It logs instead of raising on the give-up path, deliberately:
_shutdownruns inthe run loop's
finally, so raising would supersede whatever caused the shutdown, andit would make a cancelled worker surface a
RuntimeErrorinstead of aCancelledError— which would breakasyncio.wait_for(...)no longer raisingTimeoutError. It also matches the existing contract of a function that already logstask exceptions rather than raising them.
Free on the happy path:
asyncio.waitreturns as soon as the tasks finish, so normalshutdown latency is unchanged.
Verification
time, 0 hangs. Same harness and timing that previously hung.
the helper returns and the task ends cancelled), the give-up path, and the
empty-list case —
asyncio.waitraises on an empty set, so that needed a guard.Second commit: the flaky test that found this
test_procrastinate_periodic_defersgave the worker a fixed 0.1 s to start up and letthe deferrer write its row, then did
periodic_defers[-1], so a slow runner gotIndexErrorinstead of a useful message. It now waits for the row instead.That change depends on the first commit: waiting for the row means cancelling
during startup, which is precisely when the cancellation could be lost. On its own it
hung 2 runs in 8; with the fix it passes 16/16 with the race hit 4 times and recovered
each time.
Seen in CI on this run.
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Summary by CodeRabbit
Bug Fixes
Tests