The Fix
pip install celery==4.4.0rc5
Based on closed celery/celery issue #4913 · PR/commit linked
Production note: Watch p95/p99 latency and retry volume; timeouts can turn into retry storms and duplicate side-effects.
@@ -1,12 +1,13 @@
language: python
sudo: required
-dist: trusty
+dist: xenial
cache: pip
fix.md
Option A — Upgrade to fixed release\npip install celery==4.4.0rc5\nWhen NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.\n\n
Why This Fix Works in Production
- Trigger: =================================== FAILURES ===================================
- Mechanism: Added Python 3.7 support to the testing matrix in Travis CI configuration.
- Why the fix works: Added Python 3.7 support to the testing matrix in Travis CI configuration. (first fixed release: 4.4.0rc5).
Production impact:
- If left unfixed, tail latency can spike under load and surface as timeouts/retries (amplifying incident impact).
Why This Breaks in Prod
- Triggered by an upgrade/regression window: 3.7 breaks; 4.4.0rc5 is the first fixed release.
- Shows up under Python 3.7 in real deployments (not just unit tests).
- Surfaces as: =================================== FAILURES ===================================
Proof / Evidence
- GitHub issue: #4913
- Fix PR: https://github.com/celery/celery/pull/4859
- First fixed release: 4.4.0rc5
- Affected versions: 3.7
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.95
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.41
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Then why am I being told: "There's no need for this issue since we'll see those failures ourselves" How exactly is it a **bad thing**…”
“python 3.7 support will land in 4.3 release. you can use master to run 3.7. also this seems a pytest 3.4 compat issus which will…”
“@eli-schwartz auvipy's second comment was pointing you at the PR that's already open for fixing the py37 test matrix failures: https://github.com/celery/celery/pull/4859 Your comments will be…”
“in the mean time review the patch https://github.com/celery/celery/pull/4859 and suggest you inputs”
Failure Signature (Search String)
- =================================== FAILURES ===================================
Error Message
Stack trace
error.txt
Error Message
-------------
=================================== FAILURES ===================================
_______________ test_asynloop.test_poll_write_generator_stopped ________________
def Gen():
raise StopIteration()
E StopIteration
t/unit/worker/test_loops.py:375: StopIteration
The above exception was the direct cause of the following exception:
self = <t.unit.worker.test_loops.test_asynloop object at 0x7f64a7528978>
???
t/unit/worker/test_loops.py:383:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
celery/worker/loops.py:91: in asynloop
next(loop)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = <Hub@0x7f64a74a9be0: R:0 W:1>, generator = <class 'generator'>
sleep = <built-in function sleep>, min = <built-in function min>
next = <built-in function next>, Empty = <class '_queue.Empty'>
StopIteration = <class 'StopIteration'>, KeyError = <class 'KeyError'>, READ = 1
WRITE = 4, ERR = 24
def create_loop(self,
generator=generator, sleep=sleep, min=min, next=next,
Empty=Empty, StopIteration=StopIteration,
KeyError=KeyError, READ=READ, WRITE=WRITE, ERR=ERR):
readers, writers = self.readers, self.writers
poll = self.poller.poll
fire_timers = self.fire_timers
hub_remove = self.remove
scheduled = self.ti
... (truncated) ...
Environment
- Python: 3.7
What Broke
The testsuite fails to complete, causing build failures in production environments.
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==4.4.0rc5
When NOT to use: Do not use if it changes public behavior or if the failure cannot be reproduced.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/celery/celery/pull/4859
First fixed release: 4.4.0rc5
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use if it changes public behavior or if the failure cannot be reproduced.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Add a stress test that runs high-concurrency workloads and fails on thread dumps / blocked locks.
- Enable watchdog dumps in prod (faulthandler, thread dump endpoint) to capture deadlocks quickly.
- Make timeouts explicit and test them (unit + integration) to avoid silent behavior changes.
- Instrument retries (attempt count + reason) and alert on spikes to catch dependency slowdowns.
Version Compatibility Table
| Version | Status |
|---|---|
| 3.7 | Broken |
| 4.4.0rc5 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.