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https://git.anonymousland.org/anonymousland/synapse.git
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903d11c43a
* Add `DeferredCache.get_immediate` method A bunch of things that are currently calling `DeferredCache.get` are only really interested in the result if it's completed. We can optimise and simplify this case. * Remove unused 'default' parameter to DeferredCache.get() * another get_immediate instance
292 lines
9.8 KiB
Python
292 lines
9.8 KiB
Python
# -*- coding: utf-8 -*-
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# Copyright 2015, 2016 OpenMarket Ltd
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# Copyright 2018 New Vector Ltd
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# Copyright 2020 The Matrix.org Foundation C.I.C.
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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 threading
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from typing import (
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Callable,
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Generic,
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Iterable,
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MutableMapping,
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Optional,
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TypeVar,
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Union,
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cast,
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)
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from prometheus_client import Gauge
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from twisted.internet import defer
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from synapse.util.async_helpers import ObservableDeferred
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from synapse.util.caches.lrucache import LruCache
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from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
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cache_pending_metric = Gauge(
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"synapse_util_caches_cache_pending",
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"Number of lookups currently pending for this cache",
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["name"],
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)
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T = TypeVar("T")
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KT = TypeVar("KT")
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VT = TypeVar("VT")
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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 DeferredCache(Generic[KT, VT]):
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"""Wraps an LruCache, adding support for Deferred results.
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It expects that each entry added with set() will be a Deferred; likewise get()
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may return an ObservableDeferred.
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"""
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__slots__ = (
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"cache",
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"thread",
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"_pending_deferred_cache",
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)
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def __init__(
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self,
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name: str,
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max_entries: int = 1000,
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keylen: int = 1,
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tree: bool = False,
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iterable: bool = False,
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apply_cache_factor_from_config: bool = True,
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):
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"""
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Args:
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name: The name of the cache
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max_entries: Maximum amount of entries that the cache will hold
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keylen: The length of the tuple used as the cache key. Ignored unless
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`tree` is True.
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tree: Use a TreeCache instead of a dict as the underlying cache type
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iterable: If True, count each item in the cached object as an entry,
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rather than each cached object
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apply_cache_factor_from_config: Whether cache factors specified in the
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config file affect `max_entries`
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"""
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cache_type = TreeCache if tree else dict
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# _pending_deferred_cache maps from the key value to a `CacheEntry` object.
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self._pending_deferred_cache = (
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cache_type()
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) # type: MutableMapping[KT, CacheEntry]
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def metrics_cb():
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cache_pending_metric.labels(name).set(len(self._pending_deferred_cache))
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# cache is used for completed results and maps to the result itself, rather than
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# a Deferred.
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self.cache = LruCache(
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max_size=max_entries,
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keylen=keylen,
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cache_name=name,
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cache_type=cache_type,
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size_callback=(lambda d: len(d)) if iterable else None,
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metrics_collection_callback=metrics_cb,
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apply_cache_factor_from_config=apply_cache_factor_from_config,
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) # type: LruCache[KT, VT]
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self.thread = None # type: Optional[threading.Thread]
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@property
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def max_entries(self):
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return self.cache.max_size
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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(
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self,
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key: KT,
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callback: Optional[Callable[[], None]] = None,
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update_metrics: bool = True,
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) -> Union[ObservableDeferred, VT]:
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"""Looks the key up in the caches.
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Args:
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key(tuple)
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callback(fn): Gets called when the entry in the cache is invalidated
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update_metrics (bool): whether to update the cache hit rate metrics
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Returns:
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Either an ObservableDeferred or the result itself
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Raises:
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KeyError if the key is not found in the cache
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"""
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callbacks = [callback] if callback else []
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val = self._pending_deferred_cache.get(key, _Sentinel.sentinel)
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if val is not _Sentinel.sentinel:
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val.callbacks.update(callbacks)
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if update_metrics:
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m = self.cache.metrics
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assert m # we always have a name, so should always have metrics
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m.inc_hits()
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return val.deferred
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val2 = self.cache.get(
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key, _Sentinel.sentinel, callbacks=callbacks, update_metrics=update_metrics
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)
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if val2 is _Sentinel.sentinel:
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raise KeyError()
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else:
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return val2
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def get_immediate(
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self, key: KT, default: T, update_metrics: bool = True
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) -> Union[VT, T]:
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"""If we have a *completed* cached value, return it."""
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return self.cache.get(key, default, update_metrics=update_metrics)
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def set(
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self,
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key: KT,
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value: defer.Deferred,
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callback: Optional[Callable[[], None]] = None,
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) -> ObservableDeferred:
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if not isinstance(value, defer.Deferred):
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raise TypeError("not a Deferred")
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callbacks = [callback] if callback else []
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self.check_thread()
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observable = ObservableDeferred(value, consumeErrors=True)
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observer = observable.observe()
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entry = CacheEntry(deferred=observable, callbacks=callbacks)
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existing_entry = self._pending_deferred_cache.pop(key, None)
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if existing_entry:
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existing_entry.invalidate()
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self._pending_deferred_cache[key] = entry
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def compare_and_pop():
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"""Check if our entry is still the one in _pending_deferred_cache, and
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if so, pop it.
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Returns true if the entries matched.
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"""
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existing_entry = self._pending_deferred_cache.pop(key, None)
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if existing_entry is entry:
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return True
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# oops, the _pending_deferred_cache has been updated since
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# we started our query, so we are out of date.
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#
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# Better put back whatever we took out. (We do it this way
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# round, rather than peeking into the _pending_deferred_cache
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# and then removing on a match, to make the common case faster)
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if existing_entry is not None:
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self._pending_deferred_cache[key] = existing_entry
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return False
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def cb(result):
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if compare_and_pop():
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self.cache.set(key, result, entry.callbacks)
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else:
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# we're not going to put this entry into the cache, so need
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# to make sure that the invalidation callbacks are called.
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# That was probably done when _pending_deferred_cache was
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# updated, but it's possible that `set` was called without
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# `invalidate` being previously called, in which case it may
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# not have been. Either way, let's double-check now.
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entry.invalidate()
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def eb(_fail):
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compare_and_pop()
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entry.invalidate()
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# once the deferred completes, we can move the entry from the
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# _pending_deferred_cache to the real cache.
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#
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observer.addCallbacks(cb, eb)
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return observable
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def prefill(self, key: KT, value: VT, callback: Callable[[], None] = None):
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callbacks = [callback] if callback else []
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self.cache.set(key, value, callbacks=callbacks)
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def invalidate(self, key):
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self.check_thread()
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self.cache.pop(key, None)
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# if we have a pending lookup for this key, remove it from the
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# _pending_deferred_cache, which will (a) stop it being returned
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# for future queries and (b) stop it being persisted as a proper entry
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# in self.cache.
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entry = self._pending_deferred_cache.pop(key, None)
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# run the invalidation callbacks now, rather than waiting for the
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# deferred to resolve.
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if entry:
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entry.invalidate()
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def invalidate_many(self, key: KT):
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self.check_thread()
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if not isinstance(key, tuple):
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raise TypeError("The cache key must be a tuple not %r" % (type(key),))
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key = cast(KT, key)
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self.cache.del_multi(key)
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# if we have a pending lookup for this key, remove it from the
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# _pending_deferred_cache, as above
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entry_dict = self._pending_deferred_cache.pop(key, None)
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if entry_dict is not None:
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for entry in iterate_tree_cache_entry(entry_dict):
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entry.invalidate()
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def invalidate_all(self):
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self.check_thread()
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self.cache.clear()
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for entry in self._pending_deferred_cache.values():
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entry.invalidate()
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self._pending_deferred_cache.clear()
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class CacheEntry:
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__slots__ = ["deferred", "callbacks", "invalidated"]
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def __init__(
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self, deferred: ObservableDeferred, callbacks: Iterable[Callable[[], None]]
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):
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self.deferred = deferred
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self.callbacks = set(callbacks)
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self.invalidated = False
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def invalidate(self):
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if not self.invalidated:
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self.invalidated = True
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for callback in self.callbacks:
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callback()
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self.callbacks.clear()
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