RuntimeError: list changed size during iteration on asyncio PubSub get_message

[ac3673]

Environment
redis-py 6.2.0 (also happened on 6.4)
python 3.12
default parser (no hiredis)

retry = Retry(ExponentialBackoff(), 3)
client: Redis = redis.from_url(
    url
    retry=retry, 
    decode_responses=True)
pubsub: PubSub = client.pubsub()
await pubsub.subscribe(channel_1)
await pubsub.subscribe(channel_2)
while True:
    message = await pubsub.get_message(ignore_subscribe_messages=True, timeout=0.01)

Getting stack trace. Happens intermittently. I tried adjusting the timeout if it mattered but still got the error.

    message = await pubsub.get_message(ignore_subscribe_messages=True, timeout=0.01)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/apps/frontier-acm/.venv/lib/python3.12/site-packages/redis/asyncio/client.py", line 1111, in get_message
    response = await self.parse_response(block=(timeout is None), timeout=timeout)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/apps/frontier-acm/.venv/lib/python3.12/site-packages/redis/asyncio/client.py", line 984, in parse_response
    response = await self._execute(
               ^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/apps/frontier-acm/.venv/lib/python3.12/site-packages/redis/asyncio/client.py", line 964, in _execute
    return await conn.retry.call_with_retry(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/apps/frontier-acm/.venv/lib/python3.12/site-packages/redis/asyncio/retry.py", line 71, in call_with_retry
    return await do()
           ^^^^^^^^^^
  File "/home/srvc_wftcproject/apps/frontier-acm/.venv/lib/python3.12/site-packages/redis/asyncio/connection.py", line 585, in read_response
    async with async_timeout(read_timeout):
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/.local/share/uv/python/cpython-3.12.7-linux-x86_64-gnu/lib/python3.12/asyncio/timeouts.py", line 94, in __aenter__
    self.reschedule(self._when)
  File "/home/srvc_wftcproject/.local/share/uv/python/cpython-3.12.7-linux-x86_64-gnu/lib/python3.12/asyncio/timeouts.py", line 71, in reschedule
    self._timeout_handler = loop.call_at(when, self._on_timeout)
                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/srvc_wftcproject/.local/share/uv/python/cpython-3.12.7-linux-x86_64-gnu/lib/python3.12/asyncio/base_events.py", line 781, in call_at
    heapq.heappush(self._scheduled, timer)
RuntimeError: list changed size during iteration

[petyaslavova]

Hi @ac3673, thanks for reporting this! We will have a look at it soon.