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"Memcached cache backend"
import re
import time
from django.core.cache.backends.base import (
DEFAULT_TIMEOUT,
BaseCache,
InvalidCacheKey,
memcache_key_warnings,
)
from django.utils.functional import cached_property
class BaseMemcachedCache(BaseCache):
def __init__(self, server, params, library, value_not_found_exception):
super().__init__(params)
if isinstance(server, str):
self._servers = re.split("[;,]", server)
else:
self._servers = server
# Exception type raised by the underlying client library for a
# nonexistent key.
self.LibraryValueNotFoundException = value_not_found_exception
self._lib = library
self._class = library.Client
self._options = params.get("OPTIONS") or {}
@property
def client_servers(self):
return self._servers
@cached_property
def _cache(self):
"""
Implement transparent thread-safe access to a memcached client.
"""
return self._class(self.client_servers, **self._options)
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 https://github.com/memcached/memcached/wiki/Programming#expiration
# "Expiration times can be set from 0, meaning "never expire", to
# 30 days. Any time higher than 30 days is interpreted as a Unix
# timestamp date. If you want to expire an object on January 1st of
# next year, this is how you do that."
#
# This means that we have to switch to absolute timestamps.
timeout += int(time.time())
return int(timeout)
def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_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_and_validate_key(key, version=version)
return self._cache.get(key, default)
def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_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 touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_key(key, version=version)
return bool(self._cache.touch(key, self.get_backend_timeout(timeout)))
def delete(self, key, version=None):
key = self.make_and_validate_key(key, version=version)
return bool(self._cache.delete(key))
def get_many(self, keys, version=None):
key_map = {
self.make_and_validate_key(key, version=version): key for key in keys
}
ret = self._cache.get_multi(key_map.keys())
return {key_map[k]: v for k, v in ret.items()}
def close(self, **kwargs):
# Many clients don't clean up connections properly.
self._cache.disconnect_all()
def incr(self, key, delta=1, version=None):
key = self.make_and_validate_key(key, version=version)
try:
# Memcached doesn't support negative delta.
if delta < 0:
val = self._cache.decr(key, -delta)
else:
val = self._cache.incr(key, delta)
# Normalize an exception raised by the underlying client library to
# ValueError in the event of a nonexistent key when calling
# incr()/decr().
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 = {}
original_keys = {}
for key, value in data.items():
safe_key = self.make_and_validate_key(key, version=version)
safe_data[safe_key] = value
original_keys[safe_key] = key
failed_keys = self._cache.set_multi(
safe_data, self.get_backend_timeout(timeout)
)
return [original_keys[k] for k in failed_keys]
def delete_many(self, keys, version=None):
keys = [self.make_and_validate_key(key, version=version) for key in keys]
self._cache.delete_multi(keys)
def clear(self):
self._cache.flush_all()
def validate_key(self, key):
for warning in memcache_key_warnings(key):
raise InvalidCacheKey(warning)
class PyLibMCCache(BaseMemcachedCache):
"An implementation of a cache binding using pylibmc"
def __init__(self, server, params):
import pylibmc
super().__init__(
server, params, library=pylibmc, value_not_found_exception=pylibmc.NotFound
)
@property
def client_servers(self):
output = []
for server in self._servers:
output.append(server.removeprefix("unix:"))
return output
def touch(self, key, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_and_validate_key(key, version=version)
if timeout == 0:
return self._cache.delete(key)
return self._cache.touch(key, self.get_backend_timeout(timeout))
def close(self, **kwargs):
# libmemcached manages its own connections. Don't call disconnect_all()
# as it resets the failover state and creates unnecessary reconnects.
pass
class PyMemcacheCache(BaseMemcachedCache):
"""An implementation of a cache binding using pymemcache."""
def __init__(self, server, params):
import pymemcache.serde
super().__init__(
server, params, library=pymemcache, value_not_found_exception=KeyError
)
self._class = self._lib.HashClient
self._options = {
"allow_unicode_keys": True,
"default_noreply": False,
"serde": pymemcache.serde.pickle_serde,
**self._options,
}
|
