165 lines
4.7 KiB
Python
165 lines
4.7 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 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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import time
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import attr
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from sortedcontainers import SortedList
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from synapse.util.caches import register_cache
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logger = logging.getLogger(__name__)
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SENTINEL = object()
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class TTLCache:
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"""A key/value cache implementation where each entry has its own TTL"""
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def __init__(self, cache_name, timer=time.time):
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# map from key to _CacheEntry
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self._data = {}
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# the _CacheEntries, sorted by expiry time
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self._expiry_list = SortedList() # type: SortedList[_CacheEntry]
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self._timer = timer
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self._metrics = register_cache("ttl", cache_name, self, resizable=False)
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def set(self, key, value, ttl):
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"""Add/update an entry in the cache
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Args:
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key: key for this entry
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value: value for this entry
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ttl (float): TTL for this entry, in seconds
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"""
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expiry = self._timer() + ttl
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self.expire()
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e = self._data.pop(key, SENTINEL)
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if e != SENTINEL:
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self._expiry_list.remove(e)
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entry = _CacheEntry(expiry_time=expiry, ttl=ttl, key=key, value=value)
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self._data[key] = entry
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self._expiry_list.add(entry)
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def get(self, key, default=SENTINEL):
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"""Get a value from the cache
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Args:
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key: key to look up
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default: default value to return, if key is not found. If not set, and the
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key is not found, a KeyError will be raised
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Returns:
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value from the cache, or the default
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"""
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self.expire()
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e = self._data.get(key, SENTINEL)
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if e == SENTINEL:
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self._metrics.inc_misses()
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if default == SENTINEL:
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raise KeyError(key)
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return default
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self._metrics.inc_hits()
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return e.value
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def get_with_expiry(self, key):
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"""Get a value, and its expiry time, from the cache
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Args:
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key: key to look up
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Returns:
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Tuple[Any, float, float]: the value from the cache, the expiry time
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and the TTL
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Raises:
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KeyError if the entry is not found
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"""
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self.expire()
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try:
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e = self._data[key]
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except KeyError:
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self._metrics.inc_misses()
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raise
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self._metrics.inc_hits()
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return e.value, e.expiry_time, e.ttl
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def pop(self, key, default=SENTINEL):
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"""Remove a value from the cache
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If key is in the cache, remove it and return its value, else return default.
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If default is not given and key is not in the cache, a KeyError is raised.
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Args:
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key: key to look up
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default: default value to return, if key is not found. If not set, and the
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key is not found, a KeyError will be raised
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Returns:
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value from the cache, or the default
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"""
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self.expire()
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e = self._data.pop(key, SENTINEL)
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if e == SENTINEL:
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self._metrics.inc_misses()
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if default == SENTINEL:
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raise KeyError(key)
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return default
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self._expiry_list.remove(e)
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self._metrics.inc_hits()
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return e.value
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def __getitem__(self, key):
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return self.get(key)
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def __delitem__(self, key):
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self.pop(key)
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def __contains__(self, key):
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return key in self._data
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def __len__(self):
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self.expire()
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return len(self._data)
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def expire(self):
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"""Run the expiry on the cache. Any entries whose expiry times are due will
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be removed
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"""
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now = self._timer()
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while self._expiry_list:
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first_entry = self._expiry_list[0]
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if first_entry.expiry_time - now > 0.0:
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break
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del self._data[first_entry.key]
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del self._expiry_list[0]
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@attr.s(frozen=True, slots=True)
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class _CacheEntry:
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"""TTLCache entry"""
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# expiry_time is the first attribute, so that entries are sorted by expiry.
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expiry_time = attr.ib()
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ttl = attr.ib()
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key = attr.ib()
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value = attr.ib()
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