Prevent from subscribing to empty channels

[Androidown]

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Description

If an error occurs while calling self._pubsub.get_message, method _reconnect_pubsub will be called.
after the following loop is completed:

  for meta in metas:
      self.on_state_change(self._decode_result(meta), None)

all subscribed tasks might be discarded and the set self.subscribed_to will be empty. Thus a call to self._pubsub.subscribe(*self.subscribed_to) will leads the following error:

redis.exceptions.ResponseError: wrong number of arguments for 'subscribe' command

Maybe related issues:
redis/redis-py#1351
#6993

[auvipy]

i like the patch, however can you atleast provide minimal unit test?

[lgtm-com]

This pull request introduces 2 alerts when merging ad5dab8 into 5d68d78 - view on LGTM.com

new alerts:

• 2 for Wrong name for an argument in a call

[auvipy]

hey, thanks for the tests! this pr #7041 recently stabilizes the CI. could you please pull from master and check this still passes the CI?

[auvipy]

=========================== short test summary info ============================
FAILED t/unit/backends/test_mongodb.py::test_MongoBackend::test_init_mongodb_dns_seedlist
= 1 failed, 2599 passed, 17 skipped, 3 xfailed, 50 warnings in 103.53s (0:01:43) =
ERROR: InvocationError for command /home/runner/work/celery/celery/.tox/3.10-unit/bin/pytest --maxfail=10 -v --cov=celery --cov-report=xml --cov-report term (exited with code 1)
3.10-unit finish: run-test after 106.71 seconds
3.10-unit start: run-test-post

[auvipy]

but e5d9980 is green!

[hexvolt]

Still an issue in Sentry 5.2.3 (Python 3.9, redis-server 5.0.4, redis-py 3.5.3)
ResponseError: wrong number of arguments for 'subscribe' command

[auvipy]

Still an issue in Sentry 5.2.3 (Python 3.9, redis-server 5.0.4, redis-py 3.5.3) ResponseError: wrong number of arguments for 'subscribe' command

can you try #7232 ?