160 lines
5.0 KiB
Python
160 lines
5.0 KiB
Python
# Copyright (c) 2013 Red Hat, 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
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# 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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import functools
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import msgpack
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import zaqar.openstack.common.log as logging
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LOG = logging.getLogger(__name__)
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def memoized_getattr(meth):
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"""Memoizes attributes returned by __getattr__
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It can be used to remember the results from
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__getattr__ and reduce the debt of calling
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it again when the same attribute is accessed.
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This decorator memoizes attributes by setting
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them on the object itself.
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The wrapper returned by this decorator won't alter
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the returned value.
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:returns: A wrapper around the decorated method.
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"""
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@functools.wraps(meth)
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def wrapper(self, method_name):
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attr = meth(self, method_name)
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setattr(self, method_name, attr)
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return attr
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return wrapper
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def caches(keygen, ttl, cond=None):
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"""Flags a getter method as being cached using oslo.cache.
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It is assumed that the containing class defines an attribute
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named `_cache` that is an instance of an oslo.cache backend.
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The getter should raise an exception if the value can't be
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loaded, which will skip the caching step. Otherwise, the
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getter must return a value that can be encoded with
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msgpack.
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Note that you can also flag a remover method such that it
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will purge an associated item from the cache, e.g.:
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def project_cache_key(user, project=None):
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return user + ':' + str(project)
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class Project(object):
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def __init__(self, db, cache):
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self._db = db
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self._cache = cache
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@decorators.caches(project_cache_key, 60)
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def get_project(self, user, project=None):
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return self._db.get_project(user, project)
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@get_project.purges
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def del_project(self, user, project=None):
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self._db.delete_project(user, project)
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:param keygen: A static key generator function. This function
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must accept the same arguments as the getter, sans `self`.
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:param ttl: TTL for the cache entry, in seconds.
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:param cond: Conditional for whether or not to cache the
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value. Must be a function that takes a single value, and
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returns True or False.
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"""
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def purges_prop(remover):
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@functools.wraps(remover)
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def wrapper(self, *args, **kwargs):
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# First, purge from cache
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key = keygen(*args, **kwargs)
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del self._cache[key]
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# Remove/delete from origin
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remover(self, *args, **kwargs)
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return wrapper
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def prop(getter):
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@functools.wraps(getter)
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def wrapper(self, *args, **kwargs):
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key = keygen(*args, **kwargs)
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packed_value = self._cache.get(key)
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if packed_value is None:
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value = getter(self, *args, **kwargs)
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# Cache new value if desired
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if cond is None or cond(value):
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# NOTE(kgriffs): Setting use_bin_type is essential
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# for being able to distinguish between Unicode
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# and binary strings when decoding; otherwise,
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# both types are normalized to the MessagePack
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# str format family.
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packed_value = msgpack.packb(value, use_bin_type=True)
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if not self._cache.set(key, packed_value, ttl):
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LOG.warn('Failed to cache key: ' + key)
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else:
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# NOTE(kgriffs): unpackb does not default to UTF-8,
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# so we have to explicitly ask for it.
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value = msgpack.unpackb(packed_value, encoding='utf-8')
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return value
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wrapper.purges = purges_prop
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return wrapper
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return prop
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def lazy_property(write=False, delete=True):
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"""Creates a lazy property.
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:param write: Whether this property is "writable"
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:param delete: Whether this property can be deleted.
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"""
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def wrapper(fn):
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attr_name = '_lazy_' + fn.__name__
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def getter(self):
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if not hasattr(self, attr_name):
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setattr(self, attr_name, fn(self))
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return getattr(self, attr_name)
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def setter(self, value):
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setattr(self, attr_name, value)
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def deleter(self):
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delattr(self, attr_name)
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return property(fget=getter,
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fset=write and setter,
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fdel=delete and deleter,
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doc=fn.__doc__)
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return wrapper
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