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- # Copyright 2015, 2016 OpenMarket Ltd
- # Copyright 2018 New Vector Ltd
- # Copyright 2020 The Matrix.org Foundation C.I.C.
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- import enum
- import threading
- from typing import (
- Callable,
- Generic,
- Iterable,
- MutableMapping,
- Optional,
- TypeVar,
- Union,
- cast,
- )
- from prometheus_client import Gauge
- from twisted.internet import defer
- from twisted.python import failure
- from twisted.python.failure import Failure
- from synapse.util.async_helpers import ObservableDeferred
- from synapse.util.caches.lrucache import LruCache
- from synapse.util.caches.treecache import TreeCache, iterate_tree_cache_entry
- cache_pending_metric = Gauge(
- "synapse_util_caches_cache_pending",
- "Number of lookups currently pending for this cache",
- ["name"],
- )
- T = TypeVar("T")
- KT = TypeVar("KT")
- VT = TypeVar("VT")
- class _Sentinel(enum.Enum):
- # defining a sentinel in this way allows mypy to correctly handle the
- # type of a dictionary lookup.
- sentinel = object()
- class DeferredCache(Generic[KT, VT]):
- """Wraps an LruCache, adding support for Deferred results.
- It expects that each entry added with set() will be a Deferred; likewise get()
- will return a Deferred.
- """
- __slots__ = (
- "cache",
- "thread",
- "_pending_deferred_cache",
- )
- def __init__(
- self,
- name: str,
- max_entries: int = 1000,
- tree: bool = False,
- iterable: bool = False,
- apply_cache_factor_from_config: bool = True,
- prune_unread_entries: bool = True,
- ):
- """
- Args:
- name: The name of the cache
- max_entries: Maximum amount of entries that the cache will hold
- keylen: The length of the tuple used as the cache key. Ignored unless
- `tree` is True.
- tree: Use a TreeCache instead of a dict as the underlying cache type
- iterable: If True, count each item in the cached object as an entry,
- rather than each cached object
- apply_cache_factor_from_config: Whether cache factors specified in the
- config file affect `max_entries`
- """
- cache_type = TreeCache if tree else dict
- # _pending_deferred_cache maps from the key value to a `CacheEntry` object.
- self._pending_deferred_cache: Union[
- TreeCache, "MutableMapping[KT, CacheEntry]"
- ] = cache_type()
- def metrics_cb() -> None:
- cache_pending_metric.labels(name).set(len(self._pending_deferred_cache))
- # cache is used for completed results and maps to the result itself, rather than
- # a Deferred.
- self.cache: LruCache[KT, VT] = LruCache(
- max_size=max_entries,
- cache_name=name,
- cache_type=cache_type,
- size_callback=(lambda d: len(d) or 1) if iterable else None,
- metrics_collection_callback=metrics_cb,
- apply_cache_factor_from_config=apply_cache_factor_from_config,
- prune_unread_entries=prune_unread_entries,
- )
- self.thread: Optional[threading.Thread] = None
- @property
- def max_entries(self) -> int:
- return self.cache.max_size
- def check_thread(self) -> None:
- expected_thread = self.thread
- if expected_thread is None:
- self.thread = threading.current_thread()
- else:
- if expected_thread is not threading.current_thread():
- raise ValueError(
- "Cache objects can only be accessed from the main thread"
- )
- def get(
- self,
- key: KT,
- callback: Optional[Callable[[], None]] = None,
- update_metrics: bool = True,
- ) -> defer.Deferred:
- """Looks the key up in the caches.
- For symmetry with set(), this method does *not* follow the synapse logcontext
- rules: the logcontext will not be cleared on return, and the Deferred will run
- its callbacks in the sentinel context. In other words: wrap the result with
- make_deferred_yieldable() before `await`ing it.
- Args:
- key:
- callback: Gets called when the entry in the cache is invalidated
- update_metrics (bool): whether to update the cache hit rate metrics
- Returns:
- A Deferred which completes with the result. Note that this may later fail
- if there is an ongoing set() operation which later completes with a failure.
- Raises:
- KeyError if the key is not found in the cache
- """
- callbacks = [callback] if callback else []
- val = self._pending_deferred_cache.get(key, _Sentinel.sentinel)
- if val is not _Sentinel.sentinel:
- val.callbacks.update(callbacks)
- if update_metrics:
- m = self.cache.metrics
- assert m # we always have a name, so should always have metrics
- m.inc_hits()
- return val.deferred.observe()
- val2 = self.cache.get(
- key, _Sentinel.sentinel, callbacks=callbacks, update_metrics=update_metrics
- )
- if val2 is _Sentinel.sentinel:
- raise KeyError()
- else:
- return defer.succeed(val2)
- def get_immediate(
- self, key: KT, default: T, update_metrics: bool = True
- ) -> Union[VT, T]:
- """If we have a *completed* cached value, return it."""
- return self.cache.get(key, default, update_metrics=update_metrics)
- def set(
- self,
- key: KT,
- value: "defer.Deferred[VT]",
- callback: Optional[Callable[[], None]] = None,
- ) -> defer.Deferred:
- """Adds a new entry to the cache (or updates an existing one).
- The given `value` *must* be a Deferred.
- First any existing entry for the same key is invalidated. Then a new entry
- is added to the cache for the given key.
- Until the `value` completes, calls to `get()` for the key will also result in an
- incomplete Deferred, which will ultimately complete with the same result as
- `value`.
- If `value` completes successfully, subsequent calls to `get()` will then return
- a completed deferred with the same result. If it *fails*, the cache is
- invalidated and subequent calls to `get()` will raise a KeyError.
- If another call to `set()` happens before `value` completes, then (a) any
- invalidation callbacks registered in the interim will be called, (b) any
- `get()`s in the interim will continue to complete with the result from the
- *original* `value`, (c) any future calls to `get()` will complete with the
- result from the *new* `value`.
- It is expected that `value` does *not* follow the synapse logcontext rules - ie,
- if it is incomplete, it runs its callbacks in the sentinel context.
- Args:
- key: Key to be set
- value: a deferred which will complete with a result to add to the cache
- callback: An optional callback to be called when the entry is invalidated
- """
- if not isinstance(value, defer.Deferred):
- raise TypeError("not a Deferred")
- callbacks = [callback] if callback else []
- self.check_thread()
- existing_entry = self._pending_deferred_cache.pop(key, None)
- if existing_entry:
- existing_entry.invalidate()
- # XXX: why don't we invalidate the entry in `self.cache` yet?
- # we can save a whole load of effort if the deferred is ready.
- if value.called:
- result = value.result
- if not isinstance(result, failure.Failure):
- self.cache.set(key, cast(VT, result), callbacks)
- return value
- # otherwise, we'll add an entry to the _pending_deferred_cache for now,
- # and add callbacks to add it to the cache properly later.
- observable = ObservableDeferred(value, consumeErrors=True)
- observer = observable.observe()
- entry = CacheEntry(deferred=observable, callbacks=callbacks)
- self._pending_deferred_cache[key] = entry
- def compare_and_pop() -> bool:
- """Check if our entry is still the one in _pending_deferred_cache, and
- if so, pop it.
- Returns true if the entries matched.
- """
- existing_entry = self._pending_deferred_cache.pop(key, None)
- if existing_entry is entry:
- return True
- # oops, the _pending_deferred_cache has been updated since
- # we started our query, so we are out of date.
- #
- # Better put back whatever we took out. (We do it this way
- # round, rather than peeking into the _pending_deferred_cache
- # and then removing on a match, to make the common case faster)
- if existing_entry is not None:
- self._pending_deferred_cache[key] = existing_entry
- return False
- def cb(result: VT) -> None:
- if compare_and_pop():
- self.cache.set(key, result, entry.callbacks)
- else:
- # we're not going to put this entry into the cache, so need
- # to make sure that the invalidation callbacks are called.
- # That was probably done when _pending_deferred_cache was
- # updated, but it's possible that `set` was called without
- # `invalidate` being previously called, in which case it may
- # not have been. Either way, let's double-check now.
- entry.invalidate()
- def eb(_fail: Failure) -> None:
- compare_and_pop()
- entry.invalidate()
- # once the deferred completes, we can move the entry from the
- # _pending_deferred_cache to the real cache.
- #
- observer.addCallbacks(cb, eb)
- # we return a new Deferred which will be called before any subsequent observers.
- return observable.observe()
- def prefill(
- self, key: KT, value: VT, callback: Optional[Callable[[], None]] = None
- ) -> None:
- callbacks = [callback] if callback else []
- self.cache.set(key, value, callbacks=callbacks)
- def invalidate(self, key: KT) -> None:
- """Delete a key, or tree of entries
- If the cache is backed by a regular dict, then "key" must be of
- the right type for this cache
- If the cache is backed by a TreeCache, then "key" must be a tuple, but
- may be of lower cardinality than the TreeCache - in which case the whole
- subtree is deleted.
- """
- self.check_thread()
- self.cache.del_multi(key)
- # if we have a pending lookup for this key, remove it from the
- # _pending_deferred_cache, which will (a) stop it being returned
- # for future queries and (b) stop it being persisted as a proper entry
- # in self.cache.
- entry = self._pending_deferred_cache.pop(key, None)
- # run the invalidation callbacks now, rather than waiting for the
- # deferred to resolve.
- if entry:
- # _pending_deferred_cache.pop should either return a CacheEntry, or, in the
- # case of a TreeCache, a dict of keys to cache entries. Either way calling
- # iterate_tree_cache_entry on it will do the right thing.
- for entry in iterate_tree_cache_entry(entry):
- entry.invalidate()
- def invalidate_all(self) -> None:
- self.check_thread()
- self.cache.clear()
- for entry in self._pending_deferred_cache.values():
- entry.invalidate()
- self._pending_deferred_cache.clear()
- class CacheEntry:
- __slots__ = ["deferred", "callbacks", "invalidated"]
- def __init__(
- self, deferred: ObservableDeferred, callbacks: Iterable[Callable[[], None]]
- ):
- self.deferred = deferred
- self.callbacks = set(callbacks)
- self.invalidated = False
- def invalidate(self) -> None:
- if not self.invalidated:
- self.invalidated = True
- for callback in self.callbacks:
- callback()
- self.callbacks.clear()
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