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# -*- 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 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._size_estimate = 0
self.metrics = register_cache("expiring", cache_name, self)
def start(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)
if self.iterable:
self._size_estimate += len(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:
removed_len = len(value.value)
self.metrics.inc_evictions(removed_len)
self._size_estimate -= removed_len
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._size_estimate -= len(value.value)
logger.debug(
"[%s] _prune_cache before: %d, after len: %d",
self._cache_name, begin_length, len(self)
)
def __len__(self):
if self.iterable:
return self._size_estimate
else:
return len(self._cache)
class _CacheEntry(object):
def __init__(self, time, value):
self.time = time
self.value = value
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