Task cancellation shields #3037
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Introduce a proposal for task cancellation shields to allow certain code to execute regardless of task cancellation status. Implementation WIP PR: swiftlang/swift#85637
Updated reference to SE-0493 to include a link.
FranzBusch
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Nov 21, 2025
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| public func withTaskCancellationShield<T, E>( | ||
| _ operation: () throws(E) -> T, | ||
| file: String = #fileID, line: Int = #line | ||
| ) throws(E) -> T | ||
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| public nonisolated(nonsending) func withTaskCancellationShield<T, E>( | ||
| _ operation: nonisolated(nonsending) () async throws(E) -> T, // FIXME: order of attrs | ||
| file: String = #fileID, line: Int = #line | ||
| ) async throws(E) -> T |
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Can we give the generic types a slightly more descriptive name so it shows up nicely in the docs. On the PR that introduced nonisolated(nonsending) to the withTaskCancellationHandler methods we used Return and Failure for those two generic types.
Suggested change
| public func withTaskCancellationShield<T, E>( | |
| _ operation: () throws(E) -> T, | |
| file: String = #fileID, line: Int = #line | |
| ) throws(E) -> T | |
| public nonisolated(nonsending) func withTaskCancellationShield<T, E>( | |
| _ operation: nonisolated(nonsending) () async throws(E) -> T, // FIXME: order of attrs | |
| file: String = #fileID, line: Int = #line | |
| ) async throws(E) -> T | |
| public func withTaskCancellationShield<Result, Failure>( | |
| _ operation: () throws(Failure) -> Result, | |
| file: String = #fileID, line: Int = #line | |
| ) throws(Failure) -> Result | |
| public nonisolated(nonsending) func withTaskCancellationShield<Result, Failure>( | |
| _ operation: nonisolated(nonsending) () async throws(Failure) -> Result, // FIXME: order of attrs | |
| file: String = #fileID, line: Int = #line | |
| ) async throws(Failure) -> Result |
| await withTaskCancellationShield { | ||
| await withDiscardingTaskGroup { group in | ||
| group.addTask { ... } | ||
| group.cancelAll() // cancels all tasks within the group, as expected |
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This is perfect and exactly how I expected it.
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| func cleanup() { | ||
| withTaskCancellationShield { | ||
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Is this missing a slowOperation call here?
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| ```swift | ||
| extension Task where Success == Never, Failure == Never { | ||
| public static func isCancelled(ignoringCancellationShield: Bool) -> Bool |
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+1 I think that's great for debugging purposes
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Introduce a proposal for task cancellation shields to allow certain code to execute regardless of task cancellation status.
Implementation WIP PR: swiftlang/swift#85637