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"Memcached cache backend"
import pickle
import time
from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
from django.utils import six
from django.utils.deprecation import (
RemovedInDjango19Warning, RenameMethodsBase,
)
from django.utils.encoding import force_str
from django.utils.functional import cached_property
class BaseMemcachedCacheMethods(RenameMethodsBase):
renamed_methods = (
('_get_memcache_timeout', 'get_backend_timeout', RemovedInDjango19Warning),
)
class BaseMemcachedCache(six.with_metaclass(BaseMemcachedCacheMethods, BaseCache)):
def __init__(self, server, params, library, value_not_found_exception):
super(BaseMemcachedCache, self).__init__(params)
if isinstance(server, six.string_types):
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_backend_timeout(self, timeout=DEFAULT_TIMEOUT):
"""
Memcached deals with long (> 30 days) timeouts in a special
way. Call this function to obtain a safe value for your timeout.
"""
if timeout == DEFAULT_TIMEOUT:
timeout = self.default_timeout
if timeout is None:
# Using 0 in memcache sets a non-expiring timeout.
return 0
elif int(timeout) == 0:
# Other cache backends treat 0 as set-and-expire. To achieve this
# in memcache backends, a negative timeout must be passed.
timeout = -1
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 int(timeout)
def make_key(self, key, version=None):
# Python 2 memcache requires the key to be a byte string.
return force_str(super(BaseMemcachedCache, self).make_key(key, version))
def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
return self._cache.add(key, value, self.get_backend_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=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
if not self._cache.set(key, value, self.get_backend_timeout(timeout)):
# make sure the key doesn't keep its old value in case of failure to set (memcached's 1MB limit)
self._cache.delete(key)
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 = [self.make_key(x, version=version) for x in 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)
# memcached doesn't support a negative delta
if delta < 0:
return self._cache.decr(key, -delta)
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)
# memcached doesn't support a negative delta
if delta < 0:
return self._cache.incr(key, -delta)
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=DEFAULT_TIMEOUT, 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_backend_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()
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)
@property
def _cache(self):
if getattr(self, '_client', None) is None:
self._client = self._lib.Client(self._servers, pickleProtocol=pickle.HIGHEST_PROTOCOL)
return self._client
class PyLibMCCache(BaseMemcachedCache):
"An implementation of a cache binding using pylibmc"
def __init__(self, server, params):
import pylibmc
super(PyLibMCCache, self).__init__(server, params,
library=pylibmc,
value_not_found_exception=pylibmc.NotFound)
@cached_property
def _cache(self):
client = self._lib.Client(self._servers)
if self._options:
client.behaviors = self._options
return client
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