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"Thread-safe in-memory cache backend."
import pickle
import time
from contextlib import contextmanager
from django.core.cache.backends.base import DEFAULT_TIMEOUT, BaseCache
from django.utils.synch import RWLock
# Global in-memory store of cache data. Keyed by name, to provide
# multiple named local memory caches.
_caches = {}
_expire_info = {}
_locks = {}
@contextmanager
def dummy():
"""A context manager that does nothing special."""
yield
class LocMemCache(BaseCache):
def __init__(self, name, params):
BaseCache.__init__(self, params)
self._cache = _caches.setdefault(name, {})
self._expire_info = _expire_info.setdefault(name, {})
self._lock = _locks.setdefault(name, RWLock())
def add(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
with self._lock.writer():
if self._has_expired(key):
self._set(key, pickled, timeout)
return True
return False
def get(self, key, default=None, version=None, acquire_lock=True):
key = self.make_key(key, version=version)
self.validate_key(key)
pickled = None
with (self._lock.reader() if acquire_lock else dummy()):
if not self._has_expired(key):
pickled = self._cache[key]
if pickled is not None:
try:
return pickle.loads(pickled)
except pickle.PickleError:
return default
with (self._lock.writer() if acquire_lock else dummy()):
try:
del self._cache[key]
del self._expire_info[key]
except KeyError:
pass
return default
def _set(self, key, value, timeout=DEFAULT_TIMEOUT):
if len(self._cache) >= self._max_entries:
self._cull()
self._cache[key] = value
self._expire_info[key] = self.get_backend_timeout(timeout)
def set(self, key, value, timeout=DEFAULT_TIMEOUT, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
pickled = pickle.dumps(value, pickle.HIGHEST_PROTOCOL)
with self._lock.writer():
self._set(key, pickled, timeout)
def incr(self, key, delta=1, version=None):
with self._lock.writer():
value = self.get(key, version=version, acquire_lock=False)
if value is None:
raise ValueError("Key '%s' not found" % key)
new_value = value + delta
key = self.make_key(key, version=version)
pickled = pickle.dumps(new_value, pickle.HIGHEST_PROTOCOL)
self._cache[key] = pickled
return new_value
def has_key(self, key, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
with self._lock.reader():
if not self._has_expired(key):
return True
with self._lock.writer():
try:
del self._cache[key]
del self._expire_info[key]
except KeyError:
pass
return False
def _has_expired(self, key):
exp = self._expire_info.get(key, -1)
if exp is None or exp > time.time():
return False
return True
def _cull(self):
if self._cull_frequency == 0:
self.clear()
else:
doomed = [k for (i, k) in enumerate(self._cache) if i % self._cull_frequency == 0]
for k in doomed:
self._delete(k)
def _delete(self, key):
try:
del self._cache[key]
except KeyError:
pass
try:
del self._expire_info[key]
except KeyError:
pass
def delete(self, key, version=None):
key = self.make_key(key, version=version)
self.validate_key(key)
with self._lock.writer():
self._delete(key)
def clear(self):
self._cache.clear()
self._expire_info.clear()
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