fixing caching of cancelled cached tasks #1221
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TheAngryByrd
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Jan 14, 2024
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| type TaskCompletionSource<'a> with | ||
| /// https://github.com/dotnet/runtime/issues/47998 | ||
| member tcs.TrySetFromTask(real : Task<'a>) = | ||
| task { | ||
| try | ||
| let! r = real | ||
| tcs.TrySetResult r |> ignore<bool> | ||
| with | ||
| | :? OperationCanceledException as x -> tcs.TrySetCanceled(x.CancellationToken) |> ignore<bool> | ||
| | ex -> tcs.TrySetException ex |> ignore<bool> | ||
| } | ||
| |> ignore<Task<unit>> |
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Refactoring of the ContinueWith style in the previous version
| cached <- | ||
| match cached with | ||
| | null -> createCached () | ||
| | x when x.IsCompleted && not real.IsCompleted -> |
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| let! ct = CancellableTask.getCancellationToken () | ||
| let it = input.GetValue t | ||
| use _s = ct.Register(fun () -> it.Cancel()) | ||
| let! i = it |
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Most of this stuff is happening with the extension methods that use https://github.com/fsharp/FsAutoComplete/blob/9494bbf9554844dde4dcb740cd2839c6d507e414/src/FsAutoComplete.Core/AdaptiveExtensions.fs#L403-L408
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Primer
The way the AsyncAdaptive is implemented using ref-counting for tasks that depend on tasks. So if a dependent task (let's say getting a type signature hint) asks for a currently running task's result (like a typecheck) but it isn't finished, we create a
TaskCompletionSourceand transfer state to it when the "real" task is finished. This allows us to have to have many dependent sources still awaiting the typecheck (like say a codefix) but allows us to cancel the hint request if the user's mouse moves away.Main problem is we were caching those cancelled tasks while the real task may still be running. Since no updates happened, Adaptive wouldn't mark the dependent tree out of date and forever getting "Task was cancelled" in places we should recompute.