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"Memcached cache backend"
import time
from threading import local
from django.core.cache.backends.base import BaseCache, InvalidCacheBackendError
from django.utils import importlib
class BaseMemcachedCache(BaseCache):
def __init__(self, server, params, library, value_not_found_exception):
super(BaseMemcachedCache, self).__init__(params)
if isinstance(server, basestring):
self._servers = server.split(';')
else:
self._servers = server
# The exception type to catch from the underlying library for a key
# that was not found. This is a ValueError for python-memcache,
# pylibmc.NotFound for pylibmc, and cmemcache will return None without
# raising an exception.
self.LibraryValueNotFoundException = value_not_found_exception
self._lib = library
self._options = params.get('OPTIONS', None)
@property
def _cache(self):
"""
Implements transparent thread-safe access to a memcached client.
"""
if getattr(self, '_client', None) is None:
self._client = self._lib.Client(self._servers)
return self._client
def _get_memcache_timeout(self, timeout):
"""
Memcached deals with long (> 30 days) timeouts in a special
way. Call this function to obtain a safe value for your timeout.
"""
timeout = timeout or self.default_timeout
if timeout > 2592000: # 60*60*24*30, 30 days
# See http://code.google.com/p/memcached/wiki/FAQ
# "You can set expire times up to 30 days in the future. After that
# memcached interprets it as a date, and will expire the item after
# said date. This is a simple (but obscure) mechanic."
#
# This means that we have to switch to absolute timestamps.
timeout += int(time.time())
return timeout
def add(self, key, value, timeout=0, version=None):
key = self.make_key(key, version=version)
return self._cache.add(key, value, self._get_memcache_timeout(timeout))
def get(self, key, default=None, version=None):
key = self.make_key(key, version=version)
val = self._cache.get(key)
if val is None:
return default
return val
def set(self, key, value, timeout=0, version=None):
key = self.make_key(key, version=version)
self._cache.set(key, value, self._get_memcache_timeout(timeout))
def delete(self, key, version=None):
key = self.make_key(key, version=version)
self._cache.delete(key)
def get_many(self, keys, version=None):
new_keys = map(lambda x: self.make_key(x, version=version), keys)
ret = self._cache.get_multi(new_keys)
if ret:
_ = {}
m = dict(zip(new_keys, keys))
for k, v in ret.items():
_[m[k]] = v
ret = _
return ret
def close(self, **kwargs):
self._cache.disconnect_all()
def incr(self, key, delta=1, version=None):
key = self.make_key(key, version=version)
try:
val = self._cache.incr(key, delta)
# python-memcache responds to incr on non-existent keys by
# raising a ValueError, pylibmc by raising a pylibmc.NotFound
# and Cmemcache returns None. In all cases,
# we should raise a ValueError though.
except self.LibraryValueNotFoundException:
val = None
if val is None:
raise ValueError("Key '%s' not found" % key)
return val
def decr(self, key, delta=1, version=None):
key = self.make_key(key, version=version)
try:
val = self._cache.decr(key, delta)
# python-memcache responds to incr on non-existent keys by
# raising a ValueError, pylibmc by raising a pylibmc.NotFound
# and Cmemcache returns None. In all cases,
# we should raise a ValueError though.
except self.LibraryValueNotFoundException:
val = None
if val is None:
raise ValueError("Key '%s' not found" % key)
return val
def set_many(self, data, timeout=0, version=None):
safe_data = {}
for key, value in data.items():
key = self.make_key(key, version=version)
safe_data[key] = value
self._cache.set_multi(safe_data, self._get_memcache_timeout(timeout))
def delete_many(self, keys, version=None):
l = lambda x: self.make_key(x, version=version)
self._cache.delete_multi(map(l, keys))
def clear(self):
self._cache.flush_all()
# For backwards compatibility -- the default cache class tries a
# cascading lookup of cmemcache, then memcache.
class CacheClass(BaseMemcachedCache):
def __init__(self, server, params):
try:
import cmemcache as memcache
import warnings
warnings.warn(
"Support for the 'cmemcache' library has been deprecated. Please use python-memcached or pyblimc instead.",
DeprecationWarning
)
except ImportError:
try:
import memcache
except:
raise InvalidCacheBackendError(
"Memcached cache backend requires either the 'memcache' or 'cmemcache' library"
)
super(CacheClass, self).__init__(server, params,
library=memcache,
value_not_found_exception=ValueError)
class MemcachedCache(BaseMemcachedCache):
"An implementation of a cache binding using python-memcached"
def __init__(self, server, params):
import memcache
super(MemcachedCache, self).__init__(server, params,
library=memcache,
value_not_found_exception=ValueError)
class PyLibMCCache(BaseMemcachedCache):
"An implementation of a cache binding using pylibmc"
def __init__(self, server, params):
import pylibmc
self._local = local()
super(PyLibMCCache, self).__init__(server, params,
library=pylibmc,
value_not_found_exception=pylibmc.NotFound)
@property
def _cache(self):
# PylibMC uses cache options as the 'behaviors' attribute.
# It also needs to use threadlocals, because some versions of
# PylibMC don't play well with the GIL.
client = getattr(self._local, 'client', None)
if client:
return client
client = self._lib.Client(self._servers)
if self._options:
client.behaviors = self._options
self._local.client = client
return client
|
