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Python 3.14 Compatibility: asyncio.get_event_loop() raises RuntimeError #512
Description
When running arq with Python 3.14, the worker fails to start with a RuntimeError due to the deprecated asyncio.get_event_loop() behavior that is now enforced in Python 3.14.
Environment
- arq version: 0.26.3
- Python version: 3.14.2
- OS: Linux (Docker container with
python:3.14-slim)
Error
Traceback (most recent call last):
File "/app/.venv/bin/arq", line 10, in <module>
sys.exit(cli())
~~~^^
File "/app/.venv/lib/python3.14/site-packages/click/core.py", line 1485, in __call__
return self.main(*args, **kwargs)
~~~~~~~~~^^^^^^^^^^^^^^^^^
File "/app/.venv/lib/python3.14/site-packages/click/core.py", line 1406, in main
rv = self.invoke(ctx)
File "/app/.venv/lib/python3.14/site-packages/click/core.py", line 1269, in invoke
return ctx.invoke(self.callback, **ctx.params)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/.venv/lib/python3.14/site-packages/click/core.py", line 824, in invoke
return callback(*args, **kwargs)
File "/app/.venv/lib/python3.14/site-packages/arq/cli.py", line 54, in cli
run_worker(worker_settings_, **kwargs)
~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/app/.venv/lib/python3.14/site-packages/arq/worker.py", line 893, in run_worker
worker = create_worker(settings_cls, **kwargs)
File "/app/.venv/lib/python3.14/site-packages/arq/worker.py", line 889, in create_worker
return Worker(**{**get_kwargs(settings_cls), **kwargs})
File "/app/.venv/lib/python3.14/site-packages/arq/worker.py", line 269, in __init__
self.loop = asyncio.get_event_loop()
~~~~~~~~~~~~~~~~~~~~~~^^
File "/usr/local/lib/python3.14/asyncio/events.py", line 715, in get_event_loop
raise RuntimeError('There is no current event loop in thread %r.'
% threading.current_thread().name)
RuntimeError: There is no current event loop in thread 'MainThread'.
Root Cause
In Python 3.14, asyncio.get_event_loop() now raises a RuntimeError when called from a thread without a running event loop. This behavior was deprecated since Python 3.10 and is now enforced.
The issue is in arq/worker.py line 269:
self.loop = asyncio.get_event_loop()Suggested Fix
Replace:
self.loop = asyncio.get_event_loop()With:
try:
self.loop = asyncio.get_running_loop()
except RuntimeError:
self.loop = asyncio.new_event_loop()
asyncio.set_event_loop(self.loop)Or use asyncio.new_event_loop() directly where appropriate.
References
Workaround
Currently using Python 3.13 as a workaround until this is resolved.
Activity
feat(worker): TaskIQ worker skeleton + /health + /ready probes [RUS-71]
feat(worker): TaskIQ worker skeleton + /health + /ready probes [RUS-71](
Mirochill commentedon May 23, 2026
This appears to be resolved in the current release. PR #522 was merged into
v0.28.0and changedWorker.__init__()to handleasyncio.get_event_loop()raisingRuntimeErrorby creating and setting a new event loop; it also added Python 3.14 to the CI matrix. Since the reproduction above usedv0.26.3, upgrading tov0.28.0should include the fix.