Package translate :: Package misc :: Module lru
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Source Code for Module translate.misc.lru

  1  #!/usr/bin/env python 
  2  # -*- coding: utf-8 -*- 
  3  # 
  4  # Copyright 2009 Zuza Software Foundation 
  5  # 
  6  # This file is part of translate. 
  7  # 
  8  # This program is free software; you can redistribute it and/or modify 
  9  # it under the terms of the GNU General Public License as published by 
 10  # the Free Software Foundation; either version 2 of the License, or 
 11  # (at your option) any later version. 
 12  # 
 13  # This program is distributed in the hope that it will be useful, 
 14  # but WITHOUT ANY WARRANTY; without even the implied warranty of 
 15  # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 
 16  # GNU General Public License for more details. 
 17  # 
 18  # You should have received a copy of the GNU General Public License 
 19  # along with this program; if not, see <http://www.gnu.org/licenses/>. 
 20   
 21  from collections import deque 
 22  from weakref import WeakValueDictionary 
 23  import gc 
 24   
25 -class LRUCachingDict(WeakValueDictionary):
26 """Caching dictionary like object that discards the least recently 27 used objects when number of cached items exceeds maxsize. 28 29 cullsize is the fraction of items that will be discarded when 30 maxsize is reached. 31 """ 32
33 - def __init__(self, maxsize, cullsize=2, *args, **kwargs):
34 self.cullsize = max(2, cullsize) 35 self.maxsize = max(cullsize, maxsize) 36 self.queue = deque() 37 WeakValueDictionary.__init__(self, *args, **kwargs)
38
39 - def __setitem__(self, key, value):
40 # check boundaries to minimiza duplicate references 41 while len(self.queue) and self.queue[0][0] == key: 42 # item at left end of queue pop it since it'll be appended 43 # to right 44 self.queue.popleft() 45 46 while len(self.queue) and self.queue[-1][0] == key: 47 # item at right end of queue pop it since it'll be 48 # appended again 49 self.queue.pop() 50 51 if len(self) >= self.maxsize: 52 # maximum cache size exceeded, cull old items 53 # 54 # note queue is the real cache but its size is boundless 55 # since it might have duplicate references. 56 # 57 # don't bother culling if queue is smaller than weakref, 58 # this means there are too many references outside the 59 # cache, culling won't free much memory (if any). 60 while len(self) >= self.maxsize <= len(self.queue): 61 cullsize = max(int(len(self.queue) / self.cullsize), 2) 62 try: 63 for i in range(cullsize): 64 self.queue.popleft() 65 except IndexError: 66 # queue is empty, bail out. 67 #FIXME: should we force garbage collection here too? 68 break 69 70 # call garbage collecter manually since objects 71 # with circular references take some time to get 72 # collected 73 for i in range(5): 74 if gc.collect() == 0: 75 break 76 self.queue.append((key, value)) 77 WeakValueDictionary.__setitem__(self, key, value)
78 79
80 - def __getitem__(self, key):
81 value = WeakValueDictionary.__getitem__(self, key) 82 # check boundaries to minimiza duplicate references 83 while len(self.queue) > 0 and self.queue[0][0] == key: 84 # item at left end of queue pop it since it'll be appended 85 # to right 86 self.queue.popleft() 87 88 # only append if item is not at right end of queue 89 if not (len(self.queue) and self.queue[-1][0] == key): 90 self.queue.append((key, value)) 91 92 return value
93
94 - def __delitem__(self, key):
95 # can't efficiently find item in queue to delete, check 96 # boundaries. otherwise just wait till next cache purge 97 while len(self.queue) and self.queue[0][0] == key: 98 # item at left end of queue pop it since it'll be appended 99 # to right 100 self.queue.popleft() 101 102 while len(self.queue) and self.queue[-1][0] == key: 103 # item at right end of queue pop it since it'll be 104 # appended again 105 self.queue.pop() 106 107 return WeakValueDictionary.__delitem__(self, key)
108
109 - def clear(self):
110 self.queue.clear() 111 return WeakValueDictionary.clear(self)
112
113 - def setdefault(self, key, default):
114 if key not in self: 115 self[key]=default 116 117 return self[key]
118