116 lines
3.5 KiB
Python
116 lines
3.5 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015 OpenMarket Ltd
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import logging
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logger = logging.getLogger(__name__)
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class ExpiringCache(object):
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def __init__(self, cache_name, clock, max_len=0, expiry_ms=0,
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reset_expiry_on_get=False):
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"""
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Args:
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cache_name (str): Name of this cache, used for logging.
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clock (Clock)
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max_len (int): Max size of dict. If the dict grows larger than this
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then the oldest items get automatically evicted. Default is 0,
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which indicates there is no max limit.
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expiry_ms (int): How long before an item is evicted from the cache
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in milliseconds. Default is 0, indicating items never get
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evicted based on time.
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reset_expiry_on_get (bool): If true, will reset the expiry time for
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an item on access. Defaults to False.
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"""
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self._cache_name = cache_name
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self._clock = clock
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self._max_len = max_len
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self._expiry_ms = expiry_ms
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self._reset_expiry_on_get = reset_expiry_on_get
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self._cache = {}
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def start(self):
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if not self._expiry_ms:
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# Don't bother starting the loop if things never expire
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return
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def f():
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self._prune_cache()
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self._clock.looping_call(f, self._expiry_ms/2)
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def __setitem__(self, key, value):
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now = self._clock.time_msec()
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self._cache[key] = _CacheEntry(now, value)
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# Evict if there are now too many items
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if self._max_len and len(self._cache.keys()) > self._max_len:
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sorted_entries = sorted(
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self._cache.items(),
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key=lambda k, v: v.time,
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)
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for k, _ in sorted_entries[self._max_len:]:
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self._cache.pop(k)
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def __getitem__(self, key):
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entry = self._cache[key]
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if self._reset_expiry_on_get:
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entry.time = self._clock.time_msec()
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return entry.value
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def get(self, key, default=None):
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try:
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return self[key]
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except KeyError:
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return default
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def _prune_cache(self):
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if not self._expiry_ms:
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# zero expiry time means don't expire. This should never get called
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# since we have this check in start too.
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return
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begin_length = len(self._cache)
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now = self._clock.time_msec()
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keys_to_delete = set()
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for key, cache_entry in self._cache.items():
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if now - cache_entry.time > self._expiry_ms:
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keys_to_delete.add(key)
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for k in keys_to_delete:
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self._cache.pop(k)
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logger.debug(
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"[%s] _prune_cache before: %d, after len: %d",
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self._cache_name, begin_length, len(self._cache.keys())
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)
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class _CacheEntry(object):
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def __init__(self, time, value):
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self.time = time
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self.value = value
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