synapse-product/synapse/util/caches/expiringcache.py
Erik Johnston 3baf6e1667 Fix ExpiringCache.__len__ to be accurate
It used to try and produce an estimate, which was sometimes negative.
This caused metrics to be sad, so lets always just calculate it from
scratch.

(This appears to have been a longstanding bug, but one which has been made more
of a problem by #3932 and #3933).

(This was originally done by Erik as part of #3933. I'm cherry-picking it
because really it's a fix in its own right)
2018-09-26 12:32:29 +01:00

152 lines
4.7 KiB
Python

# -*- 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 itervalues
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.util.caches import register_cache
logger = logging.getLogger(__name__)
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 __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 self._cache.items():
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):
def __init__(self, time, value):
self.time = time
self.value = value