'NoneType' object has no attribute 'recv'

[BertrandBordage]

This error happens occasionally at random in my application.
The application:

• uses gunicorn --workers 1 --threads 8, so with gthread
• connects to memcached through a UNIX socket
• the application and memcached run in separate Docker Compose services, with the UNIX socket being shared through a named volume

Cache configuration in Django:

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.PyMemcacheCache',
        'LOCATION': 'unix:/var/run/memcached/memcached.sock',
        'OPTIONS': {
            'use_pooling': True,  # Keeps connections alive, more reliable with multiple threads per worker.
            'default_noreply': True,  # Do not wait for a reply when we do not need it.
            'connect_timeout': 10.0,  # seconds
            'timeout': 10.0,  # seconds
        },
    },
}

'ignore_exc': True could be specified to consider this error a cache miss (if this type of error is correctly caught), but this means we would not know whether 1% or 100% of the cache calls are failing.

Versions:
pymemcache 4.0.0
memcached 1.6.31 (from the memcached:1.6.31-alpine Docker image)
gunicorn 23.0.0
Python 3.12.4
Django 5.0.7

Relevant traceback:

  File "/srv/.local/lib/python3.12/site-packages/django/core/cache/backends/memcached.py", line 75, in get
    return self._cache.get(key, default)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/hash.py", line 347, in get
    return self._run_cmd("get", key, default, default=default, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/hash.py", line 322, in _run_cmd
    return self._safely_run_func(client, func, default_val, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/hash.py", line 211, in _safely_run_func
    result = func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/base.py", line 1494, in get
    return client.get(key, default)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/base.py", line 687, in get
    return self._fetch_cmd(b"get", [key], False, key_prefix=self.key_prefix).get(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/base.py", line 1145, in _fetch_cmd
    buf, line = _readline(self.sock, buf)
                ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/base.py", line 1658, in _readline
    buf = _recv(sock, RECV_SIZE)
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/srv/.local/lib/python3.12/site-packages/pymemcache/client/base.py", line 1750, in _recv
    return sock.recv(size)
           ^^^^^^^^^

EDIT: The memcached server was up and running at that time. docker compose ps considered it healthy for the entire day this issue happened.