forked from MirrorHub/synapse
improve typing annotations in CachedCall (#10450)
tighten up some of the typing in CachedCall, which is going to be needed when Twisted 21.7 brings better typing on Deferred.
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changelog.d/10450.misc
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changelog.d/10450.misc
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Update type annotations to work with forthcoming Twisted 21.7.0 release.
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@ -11,7 +11,7 @@
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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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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# 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 enum
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from typing import Awaitable, Callable, Generic, Optional, TypeVar, Union
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from typing import Awaitable, Callable, Generic, Optional, TypeVar, Union
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from twisted.internet.defer import Deferred
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from twisted.internet.defer import Deferred
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@ -22,6 +22,10 @@ from synapse.logging.context import make_deferred_yieldable, run_in_background
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TV = TypeVar("TV")
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TV = TypeVar("TV")
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class _Sentinel(enum.Enum):
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sentinel = object()
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class CachedCall(Generic[TV]):
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class CachedCall(Generic[TV]):
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"""A wrapper for asynchronous calls whose results should be shared
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"""A wrapper for asynchronous calls whose results should be shared
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@ -65,7 +69,7 @@ class CachedCall(Generic[TV]):
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"""
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"""
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self._callable: Optional[Callable[[], Awaitable[TV]]] = f
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self._callable: Optional[Callable[[], Awaitable[TV]]] = f
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self._deferred: Optional[Deferred] = None
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self._deferred: Optional[Deferred] = None
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self._result: Union[None, Failure, TV] = None
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self._result: Union[_Sentinel, TV, Failure] = _Sentinel.sentinel
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async def get(self) -> TV:
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async def get(self) -> TV:
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"""Kick off the call if necessary, and return the result"""
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"""Kick off the call if necessary, and return the result"""
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@ -78,8 +82,9 @@ class CachedCall(Generic[TV]):
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self._callable = None
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self._callable = None
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# once the deferred completes, store the result. We cannot simply leave the
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# once the deferred completes, store the result. We cannot simply leave the
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# result in the deferred, since if it's a Failure, GCing the deferred
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# result in the deferred, since `awaiting` a deferred destroys its result.
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# would then log a critical error about unhandled Failures.
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# (Also, if it's a Failure, GCing the deferred would log a critical error
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# about unhandled Failures)
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def got_result(r):
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def got_result(r):
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self._result = r
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self._result = r
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@ -92,13 +97,15 @@ class CachedCall(Generic[TV]):
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# and any eventual exception may not be reported.
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# and any eventual exception may not be reported.
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# we can now await the deferred, and once it completes, return the result.
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# we can now await the deferred, and once it completes, return the result.
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if isinstance(self._result, _Sentinel):
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await make_deferred_yieldable(self._deferred)
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await make_deferred_yieldable(self._deferred)
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assert not isinstance(self._result, _Sentinel)
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# I *think* this is the easiest way to correctly raise a Failure without having
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if isinstance(self._result, Failure):
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# to gut-wrench into the implementation of Deferred.
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self._result.raiseException()
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d = Deferred()
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raise AssertionError("unexpected return from Failure.raiseException")
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d.callback(self._result)
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return await d
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return self._result
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class RetryOnExceptionCachedCall(Generic[TV]):
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class RetryOnExceptionCachedCall(Generic[TV]):
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