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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.
- from synapse.util.caches import register_cache
- from collections import OrderedDict
- 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, 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():
- 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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