Package translate :: Package misc :: Module lru
[hide private]
[frames] | no frames]

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   
26 -class LRUCachingDict(WeakValueDictionary):
27 """Caching dictionary like object that discards the least recently 28 used objects when number of cached items exceeds maxsize. 29 30 cullsize is the fraction of items that will be discarded when 31 maxsize is reached. 32 """ 33
34 - def __init__(self, maxsize, cullsize=2, *args, **kwargs):
35 self.cullsize = max(2, cullsize) 36 self.maxsize = max(cullsize, maxsize) 37 self.queue = deque() 38 WeakValueDictionary.__init__(self, *args, **kwargs)
39
40 - def cull(self):
41 """free memory by deleting old items from cache""" 42 # maximum cache size exceeded, cull old items 43 # 44 # note queue is the real cache but its size is boundless 45 # since it might have duplicate references. 46 # 47 # don't bother culling if queue is smaller than weakref, 48 # this means there are too many references outside the 49 # cache, culling won't free much memory (if any). 50 while len(self) >= self.maxsize <= len(self.queue): 51 cullsize = max(int(len(self.queue) / self.cullsize), 2) 52 try: 53 for i in range(cullsize): 54 self.queue.popleft() 55 except IndexError: 56 # queue is empty, bail out. 57 #FIXME: should we force garbage collection here too? 58 break 59 60 # call garbage collecter manually since objects 61 # with circular references take some time to get 62 # collected 63 for i in xrange(5): 64 gc.collect()
65
66 - def __setitem__(self, key, value):
67 # check boundaries to minimiza duplicate references 68 while len(self.queue) and self.queue[0][0] == key: 69 # item at left end of queue pop it since it'll be appended 70 # to right 71 self.queue.popleft() 72 73 while len(self.queue) and self.queue[-1][0] == key: 74 # item at right end of queue pop it since it'll be 75 # appended again 76 self.queue.pop() 77 78 if len(self) >= self.maxsize: 79 self.cull() 80 81 self.queue.append((key, value)) 82 WeakValueDictionary.__setitem__(self, key, value)
83
84 - def __getitem__(self, key):
85 value = WeakValueDictionary.__getitem__(self, key) 86 # check boundaries to minimiza duplicate references 87 while len(self.queue) > 0 and self.queue[0][0] == key: 88 # item at left end of queue pop it since it'll be appended 89 # to right 90 self.queue.popleft() 91 92 # only append if item is not at right end of queue 93 if not (len(self.queue) and self.queue[-1][0] == key): 94 self.queue.append((key, value)) 95 96 return value
97
98 - def __delitem__(self, key):
99 # can't efficiently find item in queue to delete, check 100 # boundaries. otherwise just wait till next cache purge 101 while len(self.queue) and self.queue[0][0] == key: 102 # item at left end of queue pop it since it'll be appended 103 # to right 104 self.queue.popleft() 105 106 while len(self.queue) and self.queue[-1][0] == key: 107 # item at right end of queue pop it since it'll be 108 # appended again 109 self.queue.pop() 110 111 return WeakValueDictionary.__delitem__(self, key)
112
113 - def clear(self):
114 self.queue.clear() 115 return WeakValueDictionary.clear(self)
116
117 - def setdefault(self, key, default):
118 if key not in self: 119 self[key] = default 120 121 return self[key]
122