This document describes the current stable version of Celery (5.3). For development docs, go here.

Source code for celery.backends.cache

"""Memcached and in-memory cache result backend."""
from kombu.utils.encoding import bytes_to_str, ensure_bytes
from kombu.utils.objects import cached_property

from celery.exceptions import ImproperlyConfigured
from celery.utils.functional import LRUCache

from .base import KeyValueStoreBackend

__all__ = ('CacheBackend',)

_imp = [None]

REQUIRES_BACKEND = """\
The Memcached backend requires either pylibmc or python-memcached.\
"""

UNKNOWN_BACKEND = """\
The cache backend {0!r} is unknown,
Please use one of the following backends instead: {1}\
"""

# Global shared in-memory cache for in-memory cache client
# This is to share cache between threads
_DUMMY_CLIENT_CACHE = LRUCache(limit=5000)


def import_best_memcache():
    if _imp[0] is None:
        is_pylibmc, memcache_key_t = False, bytes_to_str
        try:
            import pylibmc as memcache
            is_pylibmc = True
        except ImportError:
            try:
                import memcache
            except ImportError:
                raise ImproperlyConfigured(REQUIRES_BACKEND)
        _imp[0] = (is_pylibmc, memcache, memcache_key_t)
    return _imp[0]


def get_best_memcache(*args, **kwargs):
    # pylint: disable=unpacking-non-sequence
    #   This is most definitely a sequence, but pylint thinks it's not.
    is_pylibmc, memcache, key_t = import_best_memcache()
    Client = _Client = memcache.Client

    if not is_pylibmc:
        def Client(*args, **kwargs):
            kwargs.pop('behaviors', None)
            return _Client(*args, **kwargs)

    return Client, key_t


class DummyClient:

    def __init__(self, *args, **kwargs):
        self.cache = _DUMMY_CLIENT_CACHE

    def get(self, key, *args, **kwargs):
        return self.cache.get(key)

    def get_multi(self, keys):
        cache = self.cache
        return {k: cache[k] for k in keys if k in cache}

    def set(self, key, value, *args, **kwargs):
        self.cache[key] = value

    def delete(self, key, *args, **kwargs):
        self.cache.pop(key, None)

    def incr(self, key, delta=1):
        return self.cache.incr(key, delta)

    def touch(self, key, expire):
        pass


backends = {
    'memcache': get_best_memcache,
    'memcached': get_best_memcache,
    'pylibmc': get_best_memcache,
    'memory': lambda: (DummyClient, ensure_bytes),
}


[docs]class CacheBackend(KeyValueStoreBackend): """Cache result backend.""" servers = None supports_autoexpire = True supports_native_join = True implements_incr = True def __init__(self, app, expires=None, backend=None, options=None, url=None, **kwargs): options = {} if not options else options super().__init__(app, **kwargs) self.url = url self.options = dict(self.app.conf.cache_backend_options, **options) self.backend = url or backend or self.app.conf.cache_backend if self.backend: self.backend, _, servers = self.backend.partition('://') self.servers = servers.rstrip('/').split(';') self.expires = self.prepare_expires(expires, type=int) try: self.Client, self.key_t = backends[self.backend]() except KeyError: raise ImproperlyConfigured(UNKNOWN_BACKEND.format( self.backend, ', '.join(backends))) self._encode_prefixes() # rencode the keyprefixes
[docs] def get(self, key): return self.client.get(key)
[docs] def mget(self, keys): return self.client.get_multi(keys)
[docs] def set(self, key, value): return self.client.set(key, value, self.expires)
[docs] def delete(self, key): return self.client.delete(key)
def _apply_chord_incr(self, header_result_args, body, **kwargs): chord_key = self.get_key_for_chord(header_result_args[0]) self.client.set(chord_key, 0, time=self.expires) return super()._apply_chord_incr( header_result_args, body, **kwargs)
[docs] def incr(self, key): return self.client.incr(key)
[docs] def expire(self, key, value): return self.client.touch(key, value)
@cached_property def client(self): return self.Client(self.servers, **self.options) def __reduce__(self, args=(), kwargs=None): kwargs = {} if not kwargs else kwargs servers = ';'.join(self.servers) backend = f'{self.backend}://{servers}/' kwargs.update( {'backend': backend, 'expires': self.expires, 'options': self.options}) return super().__reduce__(args, kwargs)
[docs] def as_uri(self, *args, **kwargs): """Return the backend as an URI. This properly handles the case of multiple servers. """ servers = ';'.join(self.servers) return f'{self.backend}://{servers}/'