145 lines
4.8 KiB
Python
145 lines
4.8 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 enum
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import logging
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import threading
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from collections import namedtuple
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from typing import Any
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from synapse.util.caches.lrucache import LruCache
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logger = logging.getLogger(__name__)
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class DictionaryEntry(namedtuple("DictionaryEntry", ("full", "known_absent", "value"))):
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"""Returned when getting an entry from the cache
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Attributes:
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full (bool): Whether the cache has the full or dict or just some keys.
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If not full then not all requested keys will necessarily be present
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in `value`
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known_absent (set): Keys that were looked up in the dict and were not
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there.
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value (dict): The full or partial dict value
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"""
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def __len__(self):
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return len(self.value)
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class _Sentinel(enum.Enum):
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# defining a sentinel in this way allows mypy to correctly handle the
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# type of a dictionary lookup.
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sentinel = object()
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class DictionaryCache:
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"""Caches key -> dictionary lookups, supporting caching partial dicts, i.e.
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fetching a subset of dictionary keys for a particular key.
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"""
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def __init__(self, name, max_entries=1000):
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self.cache = LruCache(
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max_size=max_entries, cache_name=name, size_callback=len
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) # type: LruCache[Any, DictionaryEntry]
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self.name = name
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self.sequence = 0
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self.thread = None
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def check_thread(self):
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expected_thread = self.thread
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if expected_thread is None:
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self.thread = threading.current_thread()
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else:
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if expected_thread is not threading.current_thread():
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raise ValueError(
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"Cache objects can only be accessed from the main thread"
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)
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def get(self, key, dict_keys=None):
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"""Fetch an entry out of the cache
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Args:
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key
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dict_key(list): If given a set of keys then return only those keys
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that exist in the cache.
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Returns:
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DictionaryEntry
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"""
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entry = self.cache.get(key, _Sentinel.sentinel)
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if entry is not _Sentinel.sentinel:
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if dict_keys is None:
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return DictionaryEntry(
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entry.full, entry.known_absent, dict(entry.value)
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)
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else:
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return DictionaryEntry(
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entry.full,
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entry.known_absent,
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{k: entry.value[k] for k in dict_keys if k in entry.value},
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)
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return DictionaryEntry(False, set(), {})
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def invalidate(self, key):
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self.check_thread()
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# Increment the sequence number so that any SELECT statements that
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# raced with the INSERT don't update the cache (SYN-369)
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self.sequence += 1
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self.cache.pop(key, None)
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def invalidate_all(self):
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self.check_thread()
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self.sequence += 1
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self.cache.clear()
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def update(self, sequence, key, value, fetched_keys=None):
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"""Updates the entry in the cache
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Args:
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sequence
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key (K)
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value (dict[X,Y]): The value to update the cache with.
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fetched_keys (None|set[X]): All of the dictionary keys which were
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fetched from the database.
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If None, this is the complete value for key K. Otherwise, it
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is used to infer a list of keys which we know don't exist in
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the full dict.
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"""
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self.check_thread()
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if self.sequence == sequence:
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# Only update the cache if the caches sequence number matches the
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# number that the cache had before the SELECT was started (SYN-369)
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if fetched_keys is None:
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self._insert(key, value, set())
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else:
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self._update_or_insert(key, value, fetched_keys)
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def _update_or_insert(self, key, value, known_absent):
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# We pop and reinsert as we need to tell the cache the size may have
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# changed
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entry = self.cache.pop(key, DictionaryEntry(False, set(), {}))
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entry.value.update(value)
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entry.known_absent.update(known_absent)
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self.cache[key] = entry
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def _insert(self, key, value, known_absent):
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self.cache[key] = DictionaryEntry(True, known_absent, value)
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