FailStage receives null exception when hub callback task is canceled#8064
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Arkatufus merged 2 commits intoakkadotnet:devfrom Mar 4, 2026
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…eled In PartitionHub's consumer PreStart, the OnHubReady callback checked t.IsCanceled || t.IsFaulted but passed t.Exception to FailStage. When a task is canceled (not faulted), t.Exception is null per the Task contract. FailStage(null) causes downstream ports to complete normally instead of failing, silently swallowing the cancellation. Fix: align with BroadcastHub's consumer pattern by wrapping the task through Result.FromTask(), which already handles task cancellation correctly by calling t.GetAwaiter().GetResult() to produce the real TaskCanceledException from the runtime. Note: enabling #nullable in GraphStage.cs + Hub.cs catches this at compile time (CS8604 on the FailStage call). That flagged 6 call sites total, but only this one is a real bug — the other 5 already go through Result.FromTask. Enabling nullable in these files produces ~11 additional errors and is deferred to a separate effort.
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yeah @Arkatufus is gradually working on enabling nullability from the bottom up in the |
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In PartitionHub's consumer PreStart, the OnHubReady callback checked t.IsCanceled || t.IsFaulted but passed t.Exception to FailStage. When a task is canceled (not faulted), t.Exception is null.
I used Copilot to try to understand the implications of this issue. It said:
I'm confident that the task handling is incorrect, but I need someone who knows Streams to understand if there's user impact here or not.
In either case, I fixed it by copying BroadcastHub's consumer pattern by wrapping the task through Result.FromTask(), which already handles task cancellation correctly by calling t.GetAwaiter().GetResult() to produce the real TaskCanceledException from the runtime.
Note: enabling #nullable in GraphStage.cs + Hub.cs would catch this at compile time. That's a bigger change though, so will defer that work for the moment.
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