Merge "Common decorator for caching methods"

neutron/common/utils.py

@@ -19,6 +19,7 @@
 """Utilities and helper functions."""
 
 import datetime
+import functools
 import hashlib
 import logging as std_logging
 import os
@@ -42,6 +43,64 @@ 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)
+        try:
+            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: "
+                        "%(kwargs)s"),
+                      {'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.
 
@@ -184,6 +243,12 @@ def str2dict(string):
     return res_dict
 
 
+def dict2tuple(d):
+    items = d.items()
+    items.sort()
+    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])

neutron/tests/unit/test_common_utils.py

@@ -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()
+
+    @utils.cache_method_results
+    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)
+        self.decor._cache.set.assert_called_once_with(
+            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.assertFalse(self.decor._cache.set.called)
+        self.assertEqual(self.decor._cache.get.return_value, retval)
+        self.decor._cache.get.assert_called_once_with(expected_key,
+                                                      self.not_cached)
+
+    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.assertFalse(self.decor._cache.set.called)
+        self.assertEqual(self.decor.func_retval, retval)
+        self.decor._cache.get.assert_called_once_with(expected_key,
+                                                      self.not_cached)
+
+    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)