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# -*- coding: utf-8 -*-
# Copyright 2015 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
logger = logging.getLogger(__name__)
class ExpiringCache(object):
def __init__(self, cache_name, clock, max_len=0, expiry_ms=0,
reset_expiry_on_get=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.
"""
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 = {}
def start(self):
if not self._expiry_ms:
# Don't bother starting the loop if things never expire
return
def f():
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
if self._max_len and len(self._cache.keys()) > self._max_len:
sorted_entries = sorted(
self._cache.items(),
key=lambda (k, v): v.time,
)
for k, _ in sorted_entries[self._max_len:]:
self._cache.pop(k)
def __getitem__(self, key):
entry = self._cache[key]
if self._reset_expiry_on_get:
entry.time = self._clock.time_msec()
return entry.value
def get(self, key, default=None):
try:
return self[key]
except KeyError:
return default
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._cache)
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:
self._cache.pop(k)
logger.debug(
"[%s] _prune_cache before: %d, after len: %d",
self._cache_name, begin_length, len(self._cache.keys())
)
class _CacheEntry(object):
def __init__(self, time, value):
self.time = time
self.value = value
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