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