redis Python 捕获不继承自 BaseException 的异常

Question

We're seeing exceptions in our log like the following:

ERROR Exception ignored in: <function Connection.__del__ at 0x7f9b70a5cc20>
Traceback (most recent call last):
File "/app/.heroku/python/lib/python3.7/site-packages/redis/connection.py", line 537, in __del__
File "/app/.heroku/python/lib/python3.7/site-packages/redis/connection.py", line 667, in disconnect
TypeError: catching classes that do not inherit from BaseException is not allowed

According to the Redis source code, the offending line is the except in the following snippet:

try:
    if os.getpid() == self.pid:
        shutdown(self._sock, socket.SHUT_RDWR)
    self._sock.close()
except socket.error:
    pass

Which would indicate that socket.exception doesn't inherit from BaseException. However, as far as I can tell (based on the docs and the mro class method), socket.exception does inherit from BaseException.

Why is this happening? What can I do to prevent it?

By the way, our code doesn't call Redis directly. We are using Redis Queue (rq), which is implemented using Redis.

Answer 1

This would happen if you didn't close the redis client explicitly. That's why you saw __del__ in the traceback.

I'm not using rq but I'll take celery as an example, yet the idea could also be applied to rq.

# tasks/__init__.py
from celeryapp import redis_client

@worker_shutdown.connect # this signal means it's about to shut down the worker
def cleanup(**kwargs):
    redis_client.close() # without this you may see error

# celeryapp.py
from celery import Celery
import redis

app = Celery(config_source="celeryconfig")
redis_client = redis.StrictRedis()