[Concurrency] improve cancellation handler to not hop and use caller execution context #80753
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ktoso
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The problem is that even with the #isolation parameter the non-Sendable async closure operation _still_ would potentially hop off the caller isolation. We introduced this change because the plan was the non-Sendable closure would run on the isolated parameter's isolation, but that's not actually the case: Instead, we can use the @execution(caller) on the function and closure, in order to guarantee there is no hop between those at all, and developers can trust that adding this cancellation handler will not cause any unexpected isolation changes and hops. The API was always documented to not hop as we execute the operation, so this brings the correct and expected behavior. resolves rdar://140110775
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This is blocked by incorrect behavior of the caller execution on a closure rdar://149107104 |
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The problem is that even with the #isolation parameter the non-Sendable
async closure operation still would potentially hop off the caller
isolation. We introduced this change because the plan was the
non-Sendable closure would run on the isolated parameter's isolation,
but that's not actually the case:
Instead, we can use the @execution(caller) on the function and closure,
in order to guarantee there is no hop between those at all, and
developers can trust that adding this cancellation handler will not
cause any unexpected isolation changes and hops. The API was always
documented to not hop as we execute the operation, so this brings the
correct and expected behavior.
resolves rdar://140110775