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.
| 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.
| 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 |
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| func cleanup() { | ||
| withTaskCancellationShield { | ||
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Is this missing a slowOperation call here?
Co-authored-by: Jamie <[email protected]>
| } | ||
| ``` | ||
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| However if a child task were to be cancelled explicitly the shield of the parent, has no effect on the child itself becoming cancelled: |
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This line needs editing.
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| This is sub-optimal for a few reasons: | ||
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| - We are introducing an unstructured task which needs to be scheduled to execute, and therefore delaying the timing when a cleanup may be executed, |
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In theory Task.immediate can be used to avoid the scheduling delay in a manual cancellation shield.
Of course that still doesn't work for synchronous code, still needs to pay the task creation cost, etc. So it doesn't affect the overall point of a builtin cancellation shield being preferable.
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+1 – the proposal should note this and contrast the new functionality with the current 'best' available status quo behavior.
Co-authored-by: Jamie <[email protected]>
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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