/usr/share/pyshared/mx/Misc/Cache.py is in python-egenix-mxtools 3.2.1-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 | """ Cache - Generic cache implementation
Copyright (c) 1998-2000, Marc-Andre Lemburg; mailto:mal@lemburg.com
See the documentation for further information on copyrights,
or contact the author. All Rights Reserved.
"""
import sys
from mx import Tools
# Weight table
MAXLOCALITY = 256
_weights = [1] * MAXLOCALITY
# maximal history size (must somewhat larger than MAXLOCALITY)
HISTORYLIMIT = 2 * MAXLOCALITY
# Cut goal that has to be reached (self.max_cachesize * float(DENOM / NOM))
DENOM = 3
NOM = 4
# Print debugging info ?
_debug = 0
# Init globals
class _modinit:
import math
l = Tools.frange(0,1,MAXLOCALITY)
for i,factor in Tools.irange(l):
_weights[i] = int((math.exp(factor) - 1.0) * 8192)
if _debug:
print i,'. weight =',_weights[i]
del _modinit
### Classes
class NotCached:
""" A singleton that can be used in conjunction with the .get()
method of Cache. It behaves like None.
"""
def __nonzero__(self):
return 0
__len__ = __nonzero__
NotCached = NotCached()
###
class Cache:
""" Tunable cache implementation
The following parameters influence the cache behaviour:
- max_cachesize: the cache will be cut smaller when this limit
is reached
- max_elementsize: elements with size greate than this limit
will not be cached
- locality: these many elements will be looked at in
the hit statistics to determine how important
a specific entry is
"""
data = None # Dict. of id:value cache entries
put_history = None # Reverse list of id puts; last is most
# recent access; contains id for each access
get_history = None # Reverse list of id gets; last is most
# recent access; contains id for each access
def __init__(self,max_cachesize=200,
max_elementsize=4096,
locality=50):
self.max_cachesize = max_cachesize
self.max_elementsize = max_elementsize
if locality > MAXLOCALITY:
raise ValueError,'locality must be <= %i' % MAXLOCALITY
self.locality = locality
self.cachesize = 0
self.cuts = 0
self.misses = 0
self.hits = 0
self.data = {}
self.put_history = []
self.get_history = []
def cut(self,
NOM=NOM,DENOM=DENOM):
""" Force a cut of the cache's contents.
This will make room for at least one new entry.
"""
if _debug:
print ' Cutting down cache size...'
cachesize = self.cachesize
# Cut the cache down to the entries in recent get history
newdata = {}
known_key = newdata.has_key
data = self.data
for id in self.get_history[-self.locality:]:
if known_key(id):
continue
try:
newdata[id] = data[id]
except KeyError:
pass
cachesize = len(newdata)
if _debug:
print ' Size after cut to recent history:',cachesize
# Check
if cachesize * NOM >= self.max_cachesize * DENOM:
# Calculate weights
d = {}
weights = _weights
d_get = d.get
for i,id in Tools.irange(self.get_history[-self.locality:]):
if not known_key(id):
continue
d[id] = d_get(id,0) + weights[i]
# Delete all entries left from median
ranking = Tools.sortedby(d.items(),1)
if _debug:
print ' Ranking:',ranking
for id,weight in ranking[:len(d)/2]:
if _debug:
print ' Deleting',id,'with weight =',weight
del newdata[id]
# Check
cachesize = len(newdata)
if cachesize * NOM >= self.max_cachesize * DENOM:
# Ok, so the smart way didn't work...
if _debug:
print ' Did not work, going the hard way...'
newdata.clear()
cachesize = 0
self.data = newdata
self.cachesize = cachesize
self.cuts = self.cuts + 1
def clear(self):
""" Clear the cache.
"""
self.cachesize = 0
self.data = {}
self.history = []
def get(self,id,default=NotCached,
HISTORYLIMIT=HISTORYLIMIT):
""" Get a value from the cache or return default if it is
not cached.
"""
item = self.data.get(id,None)
if item is None:
self.misses = self.misses + 1
return default
# Add "hit"
self.get_history.append(id)
if len(self.get_history) > HISTORYLIMIT:
del self.get_history[-self.locality:]
self.hits = self.hits + 1
return item
def put(self,id,value,sizeof=Tools.sizeof,
HISTORYLIMIT=HISTORYLIMIT):
""" Add a value to the cache or update an existing one.
"""
size = sizeof(value)
if size > self.max_elementsize:
return
# Adding a new entry: make sure there is room
if not self.data.has_key(id):
if _debug:
print ' Adding',id
self.cachesize = cachesize = self.cachesize + 1
if cachesize > self.max_cachesize:
self.cut()
self.data[id] = value
self.put_history.append(id)
if len(self.put_history) > HISTORYLIMIT:
del self.put_history[-self.locality:]
# Aliases
add = put
update = put
def delete(self,id):
""" Delete an entry from the cache.
It is not an error, if the entry is not currently in the cache.
"""
try:
del self.data[id]
except KeyError:
pass
# Aliases
remove = delete
###
if __name__ == '__main__':
c = Cache(10,100,locality=17)
i = 1
while 1:
print 'Round',i,c.cachesize,c.cuts,c.misses,c.data.keys(); i = i + 1
c.put(1,2)
c.get(1)
c.get(1)
c.put(5,2)
c.get(5)
c.put(2,2)
c.put(3,2)
c.get(2)
c.get(3)
c.put(2,3)
c.put(3,'x'*200)
c.get(2)
c.get(3)
c.get(2)
c.put(4,2)
c.get(4,2)
c.get(4,2)
c.get(4,2)
# Add noise
c.put(i,'x')
c.put(i * 2,'x')
c.put(i * 3,'x')
c.get(i)
|