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|
"Thread-safe in-memory cache backend."
import time
try:
import cPickle as pickle
except ImportError:
import pickle
from django.core.cache.backends.base import BaseCache
from django.utils.synch import RWLock
class CacheClass(BaseCache):
def __init__(self, _, params):
BaseCache.__init__(self, params)
self._cache = {}
self._expire_info = {}
max_entries = params.get('max_entries', 300)
try:
self._max_entries = int(max_entries)
except (ValueError, TypeError):
self._max_entries = 300
cull_frequency = params.get('cull_frequency', 3)
try:
self._cull_frequency = int(cull_frequency)
except (ValueError, TypeError):
self._cull_frequency = 3
self._lock = RWLock()
def add(self, key, value, timeout=None):
self._lock.writer_enters()
try:
exp = self._expire_info.get(key)
if exp is None or exp <= time.time():
try:
self._set(key, pickle.dumps(value), timeout)
except pickle.PickleError:
pass
finally:
self._lock.writer_leaves()
def get(self, key, default=None):
self._lock.reader_enters()
try:
exp = self._expire_info.get(key)
if exp is None:
return default
elif exp > time.time():
try:
return pickle.loads(self._cache[key])
except pickle.PickleError:
return default
finally:
self._lock.reader_leaves()
self._lock.writer_enters()
try:
del self._cache[key]
del self._expire_info[key]
return default
finally:
self._lock.writer_leaves()
def _set(self, key, value, timeout=None):
if len(self._cache) >= self._max_entries:
self._cull()
if timeout is None:
timeout = self.default_timeout
self._cache[key] = value
self._expire_info[key] = time.time() + timeout
def set(self, key, value, timeout=None):
self._lock.writer_enters()
# Python 2.3 and 2.4 don't allow combined try-except-finally blocks.
try:
try:
self._set(key, pickle.dumps(value), timeout)
except pickle.PickleError:
pass
finally:
self._lock.writer_leaves()
def has_key(self, key):
self._lock.reader_enters()
try:
exp = self._expire_info.get(key)
if exp is None:
return False
elif exp > time.time():
return True
finally:
self._lock.reader_leaves()
self._lock.writer_enters()
try:
del self._cache[key]
del self._expire_info[key]
return False
finally:
self._lock.writer_leaves()
def _cull(self):
if self._cull_frequency == 0:
self._cache.clear()
self._expire_info.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):
self._lock.writer_enters()
try:
self._delete(key)
finally:
self._lock.writer_leaves()
|
