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