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This fixes #8518 by adding a conditional check on `SyncResult` in a function when `prev_stream_token == current_stream_token`, as a sanity check. In `CachedResponse.set.<remove>()`, the result is immediately popped from the cache if the conditional function returns "false". This prevents the caching of a timed-out `SyncResult` (that has `next_key` as the stream key that produced that `SyncResult`). The cache is prevented from returning a `SyncResult` that makes the client request the same stream key over and over again, effectively making it stuck in a loop of requesting and getting a response immediately for as long as the cache keeps those values. Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>
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parent
2927921942
commit
f5c93fc993
3 changed files with 35 additions and 3 deletions
1
changelog.d/9358.misc
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1
changelog.d/9358.misc
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@ -0,0 +1 @@
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Added a fix that invalidates cache for empty timed-out sync responses.
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@ -277,8 +277,9 @@ class SyncHandler:
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user_id = sync_config.user.to_string()
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user_id = sync_config.user.to_string()
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await self.auth.check_auth_blocking(requester=requester)
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await self.auth.check_auth_blocking(requester=requester)
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res = await self.response_cache.wrap(
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res = await self.response_cache.wrap_conditional(
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sync_config.request_key,
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sync_config.request_key,
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lambda result: since_token != result.next_batch,
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self._wait_for_sync_for_user,
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self._wait_for_sync_for_user,
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sync_config,
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sync_config,
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since_token,
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since_token,
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@ -13,7 +13,7 @@
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# See the License for the specific language governing permissions and
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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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# limitations under the License.
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import logging
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import logging
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from typing import TYPE_CHECKING, Any, Callable, Dict, Generic, Optional, TypeVar
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from typing import TYPE_CHECKING, Any, Callable, Dict, Generic, Optional, Set, TypeVar
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from twisted.internet import defer
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from twisted.internet import defer
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@ -40,6 +40,7 @@ class ResponseCache(Generic[T]):
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def __init__(self, hs: "HomeServer", name: str, timeout_ms: float = 0):
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def __init__(self, hs: "HomeServer", name: str, timeout_ms: float = 0):
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# Requests that haven't finished yet.
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# Requests that haven't finished yet.
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self.pending_result_cache = {} # type: Dict[T, ObservableDeferred]
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self.pending_result_cache = {} # type: Dict[T, ObservableDeferred]
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self.pending_conditionals = {} # type: Dict[T, Set[Callable[[Any], bool]]]
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self.clock = hs.get_clock()
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self.clock = hs.get_clock()
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self.timeout_sec = timeout_ms / 1000.0
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self.timeout_sec = timeout_ms / 1000.0
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@ -101,7 +102,11 @@ class ResponseCache(Generic[T]):
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self.pending_result_cache[key] = result
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self.pending_result_cache[key] = result
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def remove(r):
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def remove(r):
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if self.timeout_sec:
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should_cache = all(
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func(r) for func in self.pending_conditionals.pop(key, [])
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)
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if self.timeout_sec and should_cache:
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self.clock.call_later(
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self.clock.call_later(
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self.timeout_sec, self.pending_result_cache.pop, key, None
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self.timeout_sec, self.pending_result_cache.pop, key, None
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)
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)
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@ -112,6 +117,31 @@ class ResponseCache(Generic[T]):
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result.addBoth(remove)
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result.addBoth(remove)
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return result.observe()
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return result.observe()
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def add_conditional(self, key: T, conditional: Callable[[Any], bool]):
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self.pending_conditionals.setdefault(key, set()).add(conditional)
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def wrap_conditional(
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self,
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key: T,
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should_cache: Callable[[Any], bool],
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callback: "Callable[..., Any]",
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*args: Any,
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**kwargs: Any
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) -> defer.Deferred:
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"""The same as wrap(), but adds a conditional to the final execution.
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When the final execution completes, *all* conditionals need to return True for it to properly cache,
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else it'll not be cached in a timed fashion.
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"""
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# See if there's already a result on this key that hasn't yet completed. Due to the single-threaded nature of
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# python, adding a key immediately in the same execution thread will not cause a race condition.
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result = self.get(key)
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if not result or isinstance(result, defer.Deferred) and not result.called:
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self.add_conditional(key, should_cache)
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return self.wrap(key, callback, *args, **kwargs)
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def wrap(
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def wrap(
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self, key: T, callback: "Callable[..., Any]", *args: Any, **kwargs: Any
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self, key: T, callback: "Callable[..., Any]", *args: Any, **kwargs: Any
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) -> defer.Deferred:
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) -> defer.Deferred:
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