diff options
Diffstat (limited to 'synapse/util/caches/response_cache.py')
| -rw-r--r-- | synapse/util/caches/response_cache.py | 99 |
1 files changed, 73 insertions, 26 deletions
diff --git a/synapse/util/caches/response_cache.py b/synapse/util/caches/response_cache.py index 25ea1bcc..34c662c4 100644 --- a/synapse/util/caches/response_cache.py +++ b/synapse/util/caches/response_cache.py @@ -12,7 +12,9 @@ # See the License for the specific language governing permissions and # limitations under the License. import logging -from typing import Any, Callable, Dict, Generic, Optional, TypeVar +from typing import Any, Awaitable, Callable, Dict, Generic, Optional, TypeVar + +import attr from twisted.internet import defer @@ -23,10 +25,36 @@ from synapse.util.caches import register_cache logger = logging.getLogger(__name__) -T = TypeVar("T") +# the type of the key in the cache +KV = TypeVar("KV") + +# the type of the result from the operation +RV = TypeVar("RV") + +@attr.s(auto_attribs=True) +class ResponseCacheContext(Generic[KV]): + """Information about a missed ResponseCache hit -class ResponseCache(Generic[T]): + This object can be passed into the callback for additional feedback + """ + + cache_key: KV + """The cache key that caused the cache miss + + This should be considered read-only. + + TODO: in attrs 20.1, make it frozen with an on_setattr. + """ + + should_cache: bool = True + """Whether the result should be cached once the request completes. + + This can be modified by the callback if it decides its result should not be cached. + """ + + +class ResponseCache(Generic[KV]): """ This caches a deferred response. Until the deferred completes it will be returned from the cache. This means that if the client retries the request @@ -35,8 +63,10 @@ class ResponseCache(Generic[T]): """ def __init__(self, clock: Clock, name: str, timeout_ms: float = 0): - # Requests that haven't finished yet. - self.pending_result_cache = {} # type: Dict[T, ObservableDeferred] + # This is poorly-named: it includes both complete and incomplete results. + # We keep complete results rather than switching to absolute values because + # that makes it easier to cache Failure results. + self.pending_result_cache = {} # type: Dict[KV, ObservableDeferred] self.clock = clock self.timeout_sec = timeout_ms / 1000.0 @@ -50,16 +80,13 @@ class ResponseCache(Generic[T]): def __len__(self) -> int: return self.size() - def get(self, key: T) -> Optional[defer.Deferred]: + def get(self, key: KV) -> Optional[defer.Deferred]: """Look up the given key. - Can return either a new Deferred (which also doesn't follow the synapse - logcontext rules), or, if the request has completed, the actual - result. You will probably want to make_deferred_yieldable the result. + Returns a new Deferred (which also doesn't follow the synapse + logcontext rules). You will probably want to make_deferred_yieldable the result. - If there is no entry for the key, returns None. It is worth noting that - this means there is no way to distinguish a completed result of None - from an absent cache entry. + If there is no entry for the key, returns None. Args: key: key to get/set in the cache @@ -76,42 +103,56 @@ class ResponseCache(Generic[T]): self._metrics.inc_misses() return None - def set(self, key: T, deferred: defer.Deferred) -> defer.Deferred: + def _set( + self, context: ResponseCacheContext[KV], deferred: defer.Deferred + ) -> defer.Deferred: """Set the entry for the given key to the given deferred. *deferred* should run its callbacks in the sentinel logcontext (ie, you should wrap normal synapse deferreds with synapse.logging.context.run_in_background). - Can return either a new Deferred (which also doesn't follow the synapse - logcontext rules), or, if *deferred* was already complete, the actual - result. You will probably want to make_deferred_yieldable the result. + Returns a new Deferred (which also doesn't follow the synapse logcontext rules). + You will probably want to make_deferred_yieldable the result. Args: - key: key to get/set in the cache + context: Information about the cache miss deferred: The deferred which resolves to the result. Returns: A new deferred which resolves to the actual result. """ result = ObservableDeferred(deferred, consumeErrors=True) + key = context.cache_key self.pending_result_cache[key] = result - def remove(r): - if self.timeout_sec: + def on_complete(r): + # if this cache has a non-zero timeout, and the callback has not cleared + # the should_cache bit, we leave it in the cache for now and schedule + # its removal later. + if self.timeout_sec and context.should_cache: self.clock.call_later( self.timeout_sec, self.pending_result_cache.pop, key, None ) else: + # otherwise, remove the result immediately. self.pending_result_cache.pop(key, None) return r - result.addBoth(remove) + # make sure we do this *after* adding the entry to pending_result_cache, + # in case the result is already complete (in which case flipping the order would + # leave us with a stuck entry in the cache). + result.addBoth(on_complete) return result.observe() - def wrap( - self, key: T, callback: Callable[..., Any], *args: Any, **kwargs: Any - ) -> defer.Deferred: + async def wrap( + self, + key: KV, + callback: Callable[..., Awaitable[RV]], + *args: Any, + cache_context: bool = False, + **kwargs: Any, + ) -> RV: """Wrap together a *get* and *set* call, taking care of logcontexts First looks up the key in the cache, and if it is present makes it @@ -140,22 +181,28 @@ class ResponseCache(Generic[T]): *args: positional parameters to pass to the callback, if it is used + cache_context: if set, the callback will be given a `cache_context` kw arg, + which will be a ResponseCacheContext object. + **kwargs: named parameters to pass to the callback, if it is used Returns: - Deferred which resolves to the result + The result of the callback (from the cache, or otherwise) """ result = self.get(key) if not result: logger.debug( "[%s]: no cached result for [%s], calculating new one", self._name, key ) + context = ResponseCacheContext(cache_key=key) + if cache_context: + kwargs["cache_context"] = context d = run_in_background(callback, *args, **kwargs) - result = self.set(key, d) + result = self._set(context, d) elif not isinstance(result, defer.Deferred) or result.called: logger.info("[%s]: using completed cached result for [%s]", self._name, key) else: logger.info( "[%s]: using incomplete cached result for [%s]", self._name, key ) - return make_deferred_yieldable(result) + return await make_deferred_yieldable(result) |