diff options
Diffstat (limited to 'synapse')
| -rw-r--r-- | synapse/util/caches/cached_call.py | 27 |
1 files changed, 17 insertions, 10 deletions
diff --git a/synapse/util/caches/cached_call.py b/synapse/util/caches/cached_call.py index 891bee0b33..e58dd91eda 100644 --- a/synapse/util/caches/cached_call.py +++ b/synapse/util/caches/cached_call.py @@ -11,7 +11,7 @@ # 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 from typing import Awaitable, Callable, Generic, Optional, TypeVar, Union from twisted.internet.defer import Deferred @@ -22,6 +22,10 @@ from synapse.logging.context import make_deferred_yieldable, run_in_background TV = TypeVar("TV") +class _Sentinel(enum.Enum): + sentinel = object() + + class CachedCall(Generic[TV]): """A wrapper for asynchronous calls whose results should be shared @@ -65,7 +69,7 @@ class CachedCall(Generic[TV]): """ self._callable: Optional[Callable[[], Awaitable[TV]]] = f self._deferred: Optional[Deferred] = None - self._result: Union[None, Failure, TV] = None + self._result: Union[_Sentinel, TV, Failure] = _Sentinel.sentinel async def get(self) -> TV: """Kick off the call if necessary, and return the result""" @@ -78,8 +82,9 @@ class CachedCall(Generic[TV]): self._callable = None # once the deferred completes, store the result. We cannot simply leave the - # result in the deferred, since if it's a Failure, GCing the deferred - # would then log a critical error about unhandled Failures. + # result in the deferred, since `awaiting` a deferred destroys its result. + # (Also, if it's a Failure, GCing the deferred would log a critical error + # about unhandled Failures) def got_result(r): self._result = r @@ -92,13 +97,15 @@ class CachedCall(Generic[TV]): # and any eventual exception may not be reported. # we can now await the deferred, and once it completes, return the result. - await make_deferred_yieldable(self._deferred) + if isinstance(self._result, _Sentinel): + await make_deferred_yieldable(self._deferred) + assert not isinstance(self._result, _Sentinel) + + if isinstance(self._result, Failure): + self._result.raiseException() + raise AssertionError("unexpected return from Failure.raiseException") - # I *think* this is the easiest way to correctly raise a Failure without having - # to gut-wrench into the implementation of Deferred. - d = Deferred() - d.callback(self._result) - return await d + return self._result class RetryOnExceptionCachedCall(Generic[TV]): |