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 cull(self):
40 """free memory by deleting old items from cache""" 41 # maximum cache size exceeded, cull old items 42 # 43 # note queue is the real cache but its size is boundless 44 # since it might have duplicate references. 45 # 46 # don't bother culling if queue is smaller than weakref, 47 # this means there are too many references outside the 48 # cache, culling won't free much memory (if any). 49 while len(self) >= self.maxsize <= len(self.queue): 50 cullsize = max(int(len(self.queue) / self.cullsize), 2) 51 try: 52 for i in range(cullsize): 53 self.queue.popleft() 54 except IndexError: 55 # queue is empty, bail out. 56 #FIXME: should we force garbage collection here too? 57 break 58 59 # call garbage collecter manually since objects 60 # with circular references take some time to get 61 # collected 62 for i in xrange(5): 63 gc.collect()
64
65 - def __setitem__(self, key, value):
66 # check boundaries to minimiza duplicate references 67 while len(self.queue) and self.queue[0][0] == key: 68 # item at left end of queue pop it since it'll be appended 69 # to right 70 self.queue.popleft() 71 72 while len(self.queue) and self.queue[-1][0] == key: 73 # item at right end of queue pop it since it'll be 74 # appended again 75 self.queue.pop() 76 77 if len(self) >= self.maxsize: 78 self.cull() 79 80 self.queue.append((key, value)) 81 WeakValueDictionary.__setitem__(self, key, value)
82
83 - def __getitem__(self, key):
84 value = WeakValueDictionary.__getitem__(self, key) 85 # check boundaries to minimiza duplicate references 86 while len(self.queue) > 0 and self.queue[0][0] == key: 87 # item at left end of queue pop it since it'll be appended 88 # to right 89 self.queue.popleft() 90 91 # only append if item is not at right end of queue 92 if not (len(self.queue) and self.queue[-1][0] == key): 93 self.queue.append((key, value)) 94 95 return value
96
97 - def __delitem__(self, key):
98 # can't efficiently find item in queue to delete, check 99 # boundaries. otherwise just wait till next cache purge 100 while len(self.queue) and self.queue[0][0] == key: 101 # item at left end of queue pop it since it'll be appended 102 # to right 103 self.queue.popleft() 104 105 while len(self.queue) and self.queue[-1][0] == key: 106 # item at right end of queue pop it since it'll be 107 # appended again 108 self.queue.pop() 109 110 return WeakValueDictionary.__delitem__(self, key)
111
112 - def clear(self):
113 self.queue.clear() 114 return WeakValueDictionary.clear(self)
115
116 - def setdefault(self, key, default):
117 if key not in self: 118 self[key] = default 119 120 return self[key]
121