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# Copyright 2008 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""Utility support for dealing with memcache."""
from google.appengine.api import memcache
from google.appengine.runtime import DeadlineExceededError
import cStringIO
import pickle
import zlib
class Key(object):
def __init__(self, key, timeout=None, compress=False):
if compress:
key += '(z)'
self._key = key
self._timeout = timeout
self._compress = compress
def get(self, compute=None):
try:
r = memcache.get(self._key)
if r and self._compress:
r = pickle.load(cStringIO.StringIO(zlib.decompress(r)))
except DeadlineExceededError:
r = None
if r is not None:
return r
if compute is not None:
r = compute()
if r is not None:
self.set(r)
return r
def clear(self):
try:
memcache.delete(self._key)
except DeadlineExceededError:
pass
def set(self, value):
try:
if self._compress:
buf = cStringIO.StringIO()
pickle.dump(value, buf, -1)
value = zlib.compress(buf.getvalue())
if self._timeout is None:
memcache.set(self._key, value)
else:
memcache.set(self._key, value, self._timeout)
except DeadlineExceededError:
pass
class CachedDict(object):
"""A cache of zero or more memcache keys. The dictionary of
acquired keys is also cached locally in this process, but
can be forcibly cleared by clear_local.
"""
def __init__(self,
prefix,
timeout,
compute_one = None,
compute_multi = None):
self._prefix = prefix
self._timeout = timeout
self._cache = {}
self._prefetch = set()
if compute_multi:
self._compute = compute_multi
elif compute_one:
self._compute = lambda x: map(compute_one, x)
else:
raise ValueError, 'compute_one or compute_multi required'
def prefetch(self, keys):
for item_key in keys:
if item_key not in self._cache:
self._prefetch.add(item_key)
def get_multi(self, keys):
result = {}
not_local = []
for item_key in keys:
try:
result[item_key] = self._cache[item_key]
except KeyError:
not_local.append(item_key)
if not_local:
to_get = []
to_get.extend(not_local)
to_get.extend(self._prefetch)
self._prefetch = set()
try:
cached = memcache.get_multi(to_get, self._prefix)
except DeadlineExceededError:
cached = {}
to_compute = []
for item_key in to_get:
try:
r = cached[item_key]
except KeyError:
to_compute.append(item_key)
continue
self._cache[item_key] = r
result[item_key] = r
if to_compute:
to_cache = {}
for item_key, r in zip(to_compute, self._compute(to_compute)):
if r is not None:
to_cache[item_key] = r
self._cache[item_key] = r
result[item_key] = r
if to_cache:
try:
memcache.set_multi(to_cache, self._timeout, self._prefix)
except DeadlineExceededError:
pass
return result
def get(self, key):
return get_multi([key])[key]
def clear_local(self):
self._cache = {}
self._prefetch = set()
def clear(self):
try:
memcache.delete_multi(self._prefix)
except DeadlineExceededError:
pass
self.clear_local()
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