1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
# -*- coding: utf-8 -*-
# decorators.py
# Copyright (C) 2013 LEAP
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.
"""
Useful decorators.
"""
import collections
import datetime
import functools
import logging
try:
from twisted.internet import defer
except ImportError:
class defer:
class Deferred:
pass
logger = logging.getLogger(__name__)
class _memoized(object):
"""
Decorator.
Caches a function's return value each time it is called.
If called later with the same arguments, the cached value is returned
(not reevaluated).
"""
# cache invalidation time, in seconds
CACHE_INVALIDATION_DELTA = 1800
def __init__(self, func, ignore_kwargs=None, is_method=False,
invalidation=None):
"""
:param ignore_kwargs: If True, ignore all kwargs.
If tuple, ignore those kwargs.
:type ignore_kwargs: bool, tuple or None
:param is_method: whether the decorated function is a method.
(ignores the self argument if so).
:type is_method: True
"""
self.ignore_kwargs = ignore_kwargs if ignore_kwargs else []
self.is_method = is_method
self.func = func
if invalidation:
self.CACHE_INVALIDATION_DELTA = invalidation
# TODO should put bounds to the cache dict so we do not
# consume a huge amount of memory.
self.cache = {}
self.cache_ts = {}
self.is_deferred = {}
def __call__(self, *args, **kwargs):
"""
Executes the call.
:tyoe args: tuple
:type kwargs: dict
"""
key = self._build_key(*args, **kwargs)
if not isinstance(key, collections.Hashable):
# uncacheable. a list, for instance.
# better to not cache than blow up.
logger.warning("Key is not hashable, bailing out!")
return self.func(*args, **kwargs)
if key in self.cache:
if self._is_cache_still_valid(key):
logger.debug("Got value from cache...")
value = self._get_value(key)
return self._ret_or_raise(value)
else:
logger.debug("Cache is invalid, evaluating again...")
# no cache, or cache invalid
try:
value = self.func(*args, **kwargs)
except Exception as exc:
logger.error("Exception while calling function: %r" % (exc,))
value = exc
if isinstance(value, defer.Deferred):
value.addBoth(self._store_deferred_value(key))
else:
self.cache[key] = value
self.is_deferred[key] = False
self.cache_ts[key] = datetime.datetime.now()
return self._ret_or_raise(value)
def _build_key(self, *args, **kwargs):
"""
Build key from the function arguments
"""
if self.is_method:
# forget about `self` as key
key_args = args[1:]
else:
key_args = args
if self.ignore_kwargs is True:
key = key_args
else:
key = (key_args, frozenset(
[(k, v) for k, v in kwargs.items()
if k not in self.ignore_kwargs]))
return key
def _get_value(self, key):
"""
Get a value form cache for a key
"""
if self.is_deferred[key]:
value = self.cache[key]
# it produces an errback if value is Failure
return defer.succeed(value)
else:
return self.cache[key]
def _ret_or_raise(self, value):
"""
Returns the value except if it is an exception,
in which case it's raised.
"""
if isinstance(value, Exception):
raise value
return value
def _is_cache_still_valid(self, key, now=datetime.datetime.now):
"""
Returns True if the cache value is still valid, False otherwise.
For now, this happen if less than CACHE_INVALIDATION_DELTA seconds
have passed from the time in which we recorded the cached value.
:param key: the key to lookup in the cache
:type key: hashable
:param now: a callable that returns a datetime object. override
for dependency injection during testing.
:type now: callable
:rtype: bool
"""
cached_ts = self.cache_ts[key]
delta = datetime.timedelta(seconds=self.CACHE_INVALIDATION_DELTA)
return (now() - cached_ts) < delta
def _store_deferred_value(self, key):
"""
Returns a callback to store values from deferreds
"""
def callback(value):
self.cache[key] = value
self.is_deferred[key] = True
return value
return callback
def __repr__(self):
"""
Return the function's docstring.
"""
return self.func.__doc__
def __get__(self, obj, objtype):
"""
Support instance methods.
"""
return functools.partial(self.__call__, obj)
def memoized_method(function=None, ignore_kwargs=None,
invalidation=_memoized.CACHE_INVALIDATION_DELTA):
"""
Wrap _memoized to allow for deferred calling
:type function: callable, or None.
:type ignore_kwargs: None, True or tuple.
:type invalidation: int seconds.
"""
if function:
return _memoized(function, is_method=True, invalidation=invalidation)
else:
def wrapper(function):
return _memoized(
function, ignore_kwargs=ignore_kwargs, is_method=True,
invalidation=invalidation)
return wrapper
|
