mirror of
https://mau.dev/maunium/synapse.git
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169 lines
5.5 KiB
Python
169 lines
5.5 KiB
Python
# 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 typing import Any, Dict, Generic, Iterable, Optional, Set, TypeVar
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import attr
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from synapse.util.caches.lrucache import LruCache
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logger = logging.getLogger(__name__)
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# The type of the cache keys.
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KT = TypeVar("KT")
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# The type of the dictionary keys.
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DKT = TypeVar("DKT")
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# The type of the dictionary values.
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DV = TypeVar("DV")
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# This class can't be generic because it uses slots with attrs.
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# See: https://github.com/python-attrs/attrs/issues/313
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@attr.s(slots=True, auto_attribs=True)
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class DictionaryEntry: # should be: Generic[DKT, DV].
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"""Returned when getting an entry from the cache
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Attributes:
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full: 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: Keys that were looked up in the dict and were not there.
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value: The full or partial dict value
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"""
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full: bool
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known_absent: Set[Any] # should be: Set[DKT]
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value: Dict[Any, Any] # should be: Dict[DKT, DV]
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def __len__(self) -> int:
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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(Generic[KT, DKT, DV]):
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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: str, max_entries: int = 1000):
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self.cache: LruCache[KT, DictionaryEntry] = LruCache(
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max_size=max_entries, cache_name=name, size_callback=len
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)
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self.name = name
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self.sequence = 0
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self.thread: Optional[threading.Thread] = None
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def check_thread(self) -> None:
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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(
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self, key: KT, dict_keys: Optional[Iterable[DKT]] = None
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) -> DictionaryEntry:
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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_keys: 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: KT) -> None:
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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) -> None:
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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(
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self,
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sequence: int,
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key: KT,
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value: Dict[DKT, DV],
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fetched_keys: Optional[Iterable[DKT]] = None,
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) -> 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
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value: The value to update the cache with.
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fetched_keys: 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(
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self, key: KT, value: Dict[DKT, DV], known_absent: Iterable[DKT]
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) -> None:
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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: DictionaryEntry = 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: KT, value: Dict[DKT, DV], known_absent: Set[DKT]) -> None:
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self.cache[key] = DictionaryEntry(True, known_absent, value)
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