Common decorator for caching methods

Decorator caches methods' results, the key is composed from function
name and its parameters. Implementation of cache itself should be in
object implementing decorated method. Cache backend should be taken
from oslo-incubator.

Related-Bug: #1276440


Change-Id: Ibe3f1b2eb10b9601ad76ec24b7f0e3551b4013e2
(cherry picked from commit 7508170498)
This commit is contained in:
Jakub Libosvar 2014-02-11 15:59:06 +01:00
parent fa41abfda9
commit 9ce5ef3536
2 changed files with 132 additions and 0 deletions

View File

@ -18,6 +18,7 @@
"""Utilities and helper functions."""
import functools
import logging as std_logging
import os
import signal
@ -38,6 +39,64 @@ SYNCHRONIZED_PREFIX = 'neutron-'
synchronized = lockutils.synchronized_with_prefix(SYNCHRONIZED_PREFIX)
class cache_method_results(object):
"""This decorator is intended for object methods only."""
def __init__(self, func):
self.func = func
functools.update_wrapper(self, func)
self._first_call = True
self._not_cached = object()
def _get_from_cache(self, target_self, *args, **kwargs):
func_name = "%(module)s.%(class)s.%(func_name)s" % {
'module': target_self.__module__,
'class': target_self.__class__.__name__,
'func_name': self.func.__name__,
key = (func_name,) + args
if kwargs:
key += dict2tuple(kwargs)
item = target_self._cache.get(key, self._not_cached)
except TypeError:
LOG.debug(_("Method %(func_name)s cannot be cached due to "
"unhashable parameters: args: %(args)s, kwargs: "
{'func_name': func_name,
'args': args,
'kwargs': kwargs})
return self.func(target_self, *args, **kwargs)
if item is self._not_cached:
item = self.func(target_self, *args, **kwargs)
target_self._cache.set(key, item, None)
return item
def __call__(self, target_self, *args, **kwargs):
if not hasattr(target_self, '_cache'):
raise NotImplementedError(
"Instance of class %(module)s.%(class)s must contain _cache "
"attribute" % {
'module': target_self.__module__,
'class': target_self.__class__.__name__})
if not target_self._cache:
if self._first_call:
LOG.debug(_("Instance of class %(module)s.%(class)s doesn't "
"contain attribute _cache therefore results "
"cannot be cached for %(func_name)s."),
{'module': target_self.__module__,
'class': target_self.__class__.__name__,
'func_name': self.func.__name__})
self._first_call = False
return self.func(target_self, *args, **kwargs)
return self._get_from_cache(target_self, *args, **kwargs)
def __get__(self, obj, objtype):
return functools.partial(self.__call__, obj)
def read_cached_file(filename, cache_info, reload_func=None):
"""Read from a file if it has been modified.
@ -180,6 +239,12 @@ def str2dict(string):
return res_dict
def dict2tuple(d):
items = d.items()
return tuple(items)
def diff_list_of_dict(old_list, new_list):
new_set = set([dict2str(l) for l in new_list])
old_set = set([dict2str(l) for l in old_list])

View File

@ -12,6 +12,7 @@
# License for the specific language governing permissions and limitations
# under the License.
import mock
import testtools
from neutron.common import exceptions as n_exc
@ -314,3 +315,69 @@ class TestDictUtils(base.BaseTestCase):
added, removed = utils.diff_list_of_dict(old_list, new_list)
self.assertEqual(added, [dict(key4="value4")])
self.assertEqual(removed, [dict(key3="value3")])
class _CachingDecorator(object):
def __init__(self):
self.func_retval = 'bar'
self._cache = mock.Mock()
def func(self, *args, **kwargs):
return self.func_retval
class TestCachingDecorator(base.BaseTestCase):
def setUp(self):
super(TestCachingDecorator, self).setUp()
self.decor = _CachingDecorator()
self.func_name = '%(module)s._CachingDecorator.func' % {
'module': self.__module__
self.not_cached = self.decor.func.func.im_self._not_cached
def test_cache_miss(self):
expected_key = (self.func_name, 1, 2, ('foo', 'bar'))
args = (1, 2)
kwargs = {'foo': 'bar'}
self.decor._cache.get.return_value = self.not_cached
retval = self.decor.func(*args, **kwargs)
expected_key, self.decor.func_retval, None)
self.assertEqual(self.decor.func_retval, retval)
def test_cache_hit(self):
expected_key = (self.func_name, 1, 2, ('foo', 'bar'))
args = (1, 2)
kwargs = {'foo': 'bar'}
retval = self.decor.func(*args, **kwargs)
self.assertEqual(self.decor._cache.get.return_value, retval)
def test_get_unhashable(self):
expected_key = (self.func_name, [1], 2)
self.decor._cache.get.side_effect = TypeError
retval = self.decor.func([1], 2)
self.assertEqual(self.decor.func_retval, retval)
def test_missing_cache(self):
delattr(self.decor, '_cache')
self.assertRaises(NotImplementedError, self.decor.func, (1, 2))
def test_no_cache(self):
self.decor._cache = False
retval = self.decor.func((1, 2))
self.assertEqual(self.decor.func_retval, retval)
class TestDict2Tuples(base.BaseTestCase):
def test_dict(self):
input_dict = {'foo': 'bar', 42: 'baz', 'aaa': 'zzz'}
expected = ((42, 'baz'), ('aaa', 'zzz'), ('foo', 'bar'))
output_tuple = utils.dict2tuple(input_dict)
self.assertEqual(expected, output_tuple)