/usr/lib/python2.7/dist-packages/sqlobject/cache.py is in python-sqlobject 1.6.0-1.
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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 | """
This implements the instance caching in SQLObject. Caching is
relatively aggressive. All objects are retained so long as they are
in memory, by keeping weak references to objects. We also keep other
objects in a cache that doesn't allow them to be garbage collected
(unless caching is turned off).
"""
import threading
from weakref import ref
from time import time as now
class CacheFactory(object):
"""
CacheFactory caches object creation. Each object should be
referenced by a single hashable ID (note tuples of hashable
values are also hashable).
"""
def __init__(self, cullFrequency=100, cullFraction=2,
cache=True):
"""
Every cullFrequency times that an item is retrieved from
this cache, the cull method is called.
The cull method then expires an arbitrary fraction of
the cached objects. The idea is at no time will the cache
be entirely emptied, placing a potentially high load at that
moment, but everything object will have its time to go
eventually. The fraction is given as an integer, and one
in that many objects are expired (i.e., the default is 1/2
of objects are expired).
By setting cache to False, items won't be cached.
However, in all cases a weak reference is kept to created
objects, and if the object hasn't been garbage collected
it will be returned.
"""
self.cullFrequency = cullFrequency
self.cullCount = 0
self.cullOffset = 0
self.cullFraction = cullFraction
self.doCache = cache
if self.doCache:
self.cache = {}
self.expiredCache = {}
self.lock = threading.Lock()
def tryGet(self, id):
"""
This returns None, or the object in cache.
"""
value = self.expiredCache.get(id)
if value:
# it's actually a weakref:
return value()
if not self.doCache:
return None
return self.cache.get(id)
def get(self, id):
"""
This method can cause deadlocks! tryGet is safer
This returns the object found in cache, or None. If None,
then the cache will remain locked! This is so that the
calling function can create the object in a threadsafe manner
before releasing the lock. You should use this like (note
that ``cache`` is actually a CacheSet object in this
example)::
obj = cache.get(some_id, my_class)
if obj is None:
try:
obj = create_object(some_id)
cache.put(some_id, my_class, obj)
finally:
cache.finishPut(cls)
This method checks both the main cache (which retains
references) and the 'expired' cache, which retains only weak
references.
"""
if self.doCache:
if self.cullCount > self.cullFrequency:
# Two threads could hit the cull in a row, but
# that's not so bad. At least by setting cullCount
# back to zero right away we avoid this. The cull
# method has a lock, so it's threadsafe.
self.cullCount = 0
self.cull()
else:
self.cullCount = self.cullCount + 1
try:
return self.cache[id]
except KeyError:
pass
self.lock.acquire()
try:
val = self.cache[id]
except KeyError:
pass
else:
self.lock.release()
return val
try:
val = self.expiredCache[id]()
except KeyError:
return None
else:
del self.expiredCache[id]
if val is None:
return None
self.cache[id] = val
self.lock.release()
return val
else:
try:
val = self.expiredCache[id]()
if val is not None:
return val
except KeyError:
pass
self.lock.acquire()
try:
val = self.expiredCache[id]()
except KeyError:
return None
else:
if val is None:
del self.expiredCache[id]
return None
self.lock.release()
return val
def put(self, id, obj):
"""
Puts an object into the cache. Should only be called after
.get(), so that duplicate objects don't end up in the cache.
"""
if self.doCache:
self.cache[id] = obj
else:
self.expiredCache[id] = ref(obj)
def finishPut(self):
"""
Releases the lock that is retained when .get() is called and
returns None.
"""
self.lock.release()
def created(self, id, obj):
"""
Inserts and object into the cache. Should be used when no one
else knows about the object yet, so there cannot be any object
already in the cache. After a database INSERT is an example
of this situation.
"""
if self.doCache:
if self.cullCount > self.cullFrequency:
# Two threads could hit the cull in a row, but
# that's not so bad. At least by setting cullCount
# back to zero right away we avoid this. The cull
# method has a lock, so it's threadsafe.
self.cullCount = 0
self.cull()
else:
self.cullCount = self.cullCount + 1
self.cache[id] = obj
else:
self.expiredCache[id] = ref(obj)
def cull(self):
"""Runs through the cache and expires objects
E.g., if ``cullFraction`` is 3, then every third object is moved to
the 'expired' (aka weakref) cache.
"""
self.lock.acquire()
try:
#remove dead references from the expired cache
keys = self.expiredCache.keys()
for key in keys:
if self.expiredCache[key]() is None:
self.expiredCache.pop(key, None)
keys = self.cache.keys()
for i in xrange(self.cullOffset, len(keys), self.cullFraction):
id = keys[i]
# create a weakref, then remove from the cache
obj = ref(self.cache[id])
del self.cache[id]
#the object may have been gc'd when removed from the cache
#above, no need to place in expiredCache
if obj() is not None:
self.expiredCache[id] = obj
# This offset tries to balance out which objects we
# expire, so no object will just hang out in the cache
# forever.
self.cullOffset = (self.cullOffset + 1) % self.cullFraction
finally:
self.lock.release()
def clear(self):
"""
Removes everything from the cache. Warning! This can cause
duplicate objects in memory.
"""
if self.doCache:
self.cache.clear()
self.expiredCache.clear()
def expire(self, id):
"""
Expires a single object. Typically called after a delete.
Doesn't even keep a weakref. (@@: bad name?)
"""
if not self.doCache:
return
self.lock.acquire()
try:
if id in self.cache:
del self.cache[id]
if id in self.expiredCache:
del self.expiredCache[id]
finally:
self.lock.release()
def expireAll(self):
"""
Expires all objects, moving them all into the expired/weakref
cache.
"""
if not self.doCache:
return
self.lock.acquire()
try:
for key, value in self.cache.items():
self.expiredCache[key] = ref(value)
self.cache = {}
finally:
self.lock.release()
def allIDs(self):
"""
Returns the IDs of all objects in the cache.
"""
if self.doCache:
all = self.cache.keys()
else:
all = []
for id, value in self.expiredCache.items():
if value():
all.append(id)
return all
def getAll(self):
"""
Return all the objects in the cache.
"""
if self.doCache:
all = self.cache.values()
else:
all = []
for value in self.expiredCache.values():
if value():
all.append(value())
return all
class CacheSet(object):
"""
A CacheSet is used to collect and maintain a series of caches. In
SQLObject, there is one CacheSet per connection, and one Cache
in the CacheSet for each class, since IDs are not unique across
classes. It contains methods similar to Cache, but that take
a ``cls`` argument.
"""
def __init__(self, *args, **kw):
self.caches = {}
self.args = args
self.kw = kw
def get(self, id, cls):
try:
return self.caches[cls.__name__].get(id)
except KeyError:
self.caches[cls.__name__] = CacheFactory(*self.args, **self.kw)
return self.caches[cls.__name__].get(id)
def put(self, id, cls, obj):
self.caches[cls.__name__].put(id, obj)
def finishPut(self, cls):
self.caches[cls.__name__].finishPut()
def created(self, id, cls, obj):
try:
self.caches[cls.__name__].created(id, obj)
except KeyError:
self.caches[cls.__name__] = CacheFactory(*self.args, **self.kw)
self.caches[cls.__name__].created(id, obj)
def expire(self, id, cls):
try:
self.caches[cls.__name__].expire(id)
except KeyError:
pass
def clear(self, cls=None):
if cls is None:
for cache in self.caches.values():
cache.clear()
elif cls.__name__ in self.caches:
self.caches[cls.__name__].clear()
def tryGet(self, id, cls):
return self.tryGetByName(id, cls.__name__)
def tryGetByName(self, id, clsname):
try:
return self.caches[clsname].tryGet(id)
except KeyError:
return None
def allIDs(self, cls):
try:
self.caches[cls.__name__].allIDs()
except KeyError:
return []
def allSubCaches(self):
return self.caches.values()
def allSubCachesByClassNames(self):
return self.caches
def weakrefAll(self, cls=None):
"""
Move all objects in the cls (or if not given, then in all
classes) to the weakref dictionary, where they can be
collected.
"""
if cls is None:
for cache in self.caches.values():
cache.expireAll()
elif cls.__name__ in self.caches:
self.caches[cls.__name__].expireAll()
def getAll(self, cls=None):
"""
Returns all instances in the cache for the given class or all
classes.
"""
if cls is None:
results = []
for cache in self.caches.values():
results.extend(cache.getAll())
return results
elif cls.__name__ in self.caches:
return self.caches[cls.__name__].getAll()
else:
return []
|