summary refs log tree commit diff
path: root/synapse/util/caches/expiringcache.py
blob: cddf1ed51521bc1ae89e9740c2f9c04ef0736499 (plain) (blame)
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
# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import logging
from collections import OrderedDict

from six import iteritems, itervalues

from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.util.caches import register_cache

logger = logging.getLogger(__name__)


SENTINEL = object()


class ExpiringCache(object):
    def __init__(
        self,
        cache_name,
        clock,
        max_len=0,
        expiry_ms=0,
        reset_expiry_on_get=False,
        iterable=False,
    ):
        """
        Args:
            cache_name (str): Name of this cache, used for logging.
            clock (Clock)
            max_len (int): Max size of dict. If the dict grows larger than this
                then the oldest items get automatically evicted. Default is 0,
                which indicates there is no max limit.
            expiry_ms (int): How long before an item is evicted from the cache
                in milliseconds. Default is 0, indicating items never get
                evicted based on time.
            reset_expiry_on_get (bool): If true, will reset the expiry time for
                an item on access. Defaults to False.
            iterable (bool): If true, the size is calculated by summing the
                sizes of all entries, rather than the number of entries.

        """
        self._cache_name = cache_name

        self._clock = clock

        self._max_len = max_len
        self._expiry_ms = expiry_ms

        self._reset_expiry_on_get = reset_expiry_on_get

        self._cache = OrderedDict()

        self.iterable = iterable

        self.metrics = register_cache("expiring", cache_name, self)

        if not self._expiry_ms:
            # Don't bother starting the loop if things never expire
            return

        def f():
            return run_as_background_process(
                "prune_cache_%s" % self._cache_name, self._prune_cache
            )

        self._clock.looping_call(f, self._expiry_ms / 2)

    def __setitem__(self, key, value):
        now = self._clock.time_msec()
        self._cache[key] = _CacheEntry(now, value)

        # Evict if there are now too many items
        while self._max_len and len(self) > self._max_len:
            _key, value = self._cache.popitem(last=False)
            if self.iterable:
                self.metrics.inc_evictions(len(value.value))
            else:
                self.metrics.inc_evictions()

    def __getitem__(self, key):
        try:
            entry = self._cache[key]
            self.metrics.inc_hits()
        except KeyError:
            self.metrics.inc_misses()
            raise

        if self._reset_expiry_on_get:
            entry.time = self._clock.time_msec()

        return entry.value

    def pop(self, key, default=SENTINEL):
        """Removes and returns the value with the given key from the cache.

        If the key isn't in the cache then `default` will be returned if
        specified, otherwise `KeyError` will get raised.

        Identical functionality to `dict.pop(..)`.
        """

        value = self._cache.pop(key, default)
        if value is SENTINEL:
            raise KeyError(key)

        return value

    def __contains__(self, key):
        return key in self._cache

    def get(self, key, default=None):
        try:
            return self[key]
        except KeyError:
            return default

    def setdefault(self, key, value):
        try:
            return self[key]
        except KeyError:
            self[key] = value
            return value

    def _prune_cache(self):
        if not self._expiry_ms:
            # zero expiry time means don't expire. This should never get called
            # since we have this check in start too.
            return
        begin_length = len(self)

        now = self._clock.time_msec()

        keys_to_delete = set()

        for key, cache_entry in iteritems(self._cache):
            if now - cache_entry.time > self._expiry_ms:
                keys_to_delete.add(key)

        for k in keys_to_delete:
            value = self._cache.pop(k)
            if self.iterable:
                self.metrics.inc_evictions(len(value.value))
            else:
                self.metrics.inc_evictions()

        logger.debug(
            "[%s] _prune_cache before: %d, after len: %d",
            self._cache_name,
            begin_length,
            len(self),
        )

    def __len__(self):
        if self.iterable:
            return sum(len(entry.value) for entry in itervalues(self._cache))
        else:
            return len(self._cache)


class _CacheEntry(object):
    __slots__ = ["time", "value"]

    def __init__(self, time, value):
        self.time = time
        self.value = value