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1 "Thread-safe in-memory cache backend." |
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2 |
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3 import time |
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4 try: |
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5 import cPickle as pickle |
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6 except ImportError: |
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7 import pickle |
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8 |
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9 from django.core.cache.backends.base import BaseCache |
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10 from django.utils.synch import RWLock |
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11 |
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12 class CacheClass(BaseCache): |
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13 def __init__(self, _, params): |
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14 BaseCache.__init__(self, params) |
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15 self._cache = {} |
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16 self._expire_info = {} |
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17 |
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18 max_entries = params.get('max_entries', 300) |
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19 try: |
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20 self._max_entries = int(max_entries) |
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21 except (ValueError, TypeError): |
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22 self._max_entries = 300 |
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23 |
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24 cull_frequency = params.get('cull_frequency', 3) |
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25 try: |
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26 self._cull_frequency = int(cull_frequency) |
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27 except (ValueError, TypeError): |
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28 self._cull_frequency = 3 |
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29 |
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30 self._lock = RWLock() |
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31 |
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32 def add(self, key, value, timeout=None): |
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33 self._lock.writer_enters() |
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34 try: |
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35 exp = self._expire_info.get(key) |
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36 if exp is None or exp <= time.time(): |
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37 try: |
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38 self._set(key, pickle.dumps(value), timeout) |
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39 except pickle.PickleError: |
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40 pass |
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41 finally: |
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42 self._lock.writer_leaves() |
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43 |
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44 def get(self, key, default=None): |
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45 self._lock.reader_enters() |
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46 try: |
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47 exp = self._expire_info.get(key) |
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48 if exp is None: |
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49 return default |
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50 elif exp > time.time(): |
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51 try: |
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52 return pickle.loads(self._cache[key]) |
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53 except pickle.PickleError: |
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54 return default |
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55 finally: |
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56 self._lock.reader_leaves() |
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57 self._lock.writer_enters() |
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58 try: |
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59 del self._cache[key] |
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60 del self._expire_info[key] |
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61 return default |
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62 finally: |
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63 self._lock.writer_leaves() |
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64 |
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65 def _set(self, key, value, timeout=None): |
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66 if len(self._cache) >= self._max_entries: |
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67 self._cull() |
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68 if timeout is None: |
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69 timeout = self.default_timeout |
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70 self._cache[key] = value |
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71 self._expire_info[key] = time.time() + timeout |
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72 |
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73 def set(self, key, value, timeout=None): |
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74 self._lock.writer_enters() |
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75 # Python 2.3 and 2.4 don't allow combined try-except-finally blocks. |
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76 try: |
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77 try: |
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78 self._set(key, pickle.dumps(value), timeout) |
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79 except pickle.PickleError: |
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80 pass |
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81 finally: |
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82 self._lock.writer_leaves() |
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83 |
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84 def has_key(self, key): |
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85 self._lock.reader_enters() |
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86 try: |
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87 exp = self._expire_info.get(key) |
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88 if exp is None: |
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89 return False |
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90 elif exp > time.time(): |
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91 return True |
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92 finally: |
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93 self._lock.reader_leaves() |
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94 |
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95 self._lock.writer_enters() |
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96 try: |
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97 del self._cache[key] |
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98 del self._expire_info[key] |
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99 return False |
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100 finally: |
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101 self._lock.writer_leaves() |
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102 |
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103 def _cull(self): |
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104 if self._cull_frequency == 0: |
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105 self._cache.clear() |
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106 self._expire_info.clear() |
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107 else: |
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108 doomed = [k for (i, k) in enumerate(self._cache) if i % self._cull_frequency == 0] |
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109 for k in doomed: |
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110 self.delete(k) |
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111 |
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112 def _delete(self, key): |
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113 try: |
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114 del self._cache[key] |
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115 except KeyError: |
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116 pass |
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117 try: |
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118 del self._expire_info[key] |
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119 except KeyError: |
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120 pass |
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121 |
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122 def delete(self, key): |
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123 self._lock.writer_enters() |
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124 try: |
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125 self._delete(key) |
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126 finally: |
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127 self._lock.writer_leaves() |