Enforce Sendability in EventLoopFuture and EventLoopPromise methods
#2501
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FranzBusch
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Aug 11, 2023
| } | ||
| return next.futureResult | ||
| public func flatMapWithEventLoop<NewValue: Sendable>(_ callback: @escaping @Sendable (Value, EventLoop) -> EventLoopFuture<NewValue>) -> EventLoopFuture<NewValue> { | ||
| // Is this the same thing and still fast? |
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I am not sure about this one. Probably the previous implementation was faster but I wasn't really sure here
# Motivation With apple#2496 we fixed a Sendability checking hole by removing the unconditional conformance of `EventLoopFuture/Promise` to `Sendable`. This was the correct thing to do; however, it has the fallout that a couple of methods are now rightly complaining that their values are send across isolation domains. # Modification This PR requires values on some `ELF/P` methods to be `Sendable` when we might potentially transfer the values across isolation domains/ELs. We have to be overly aggressive here because we do not know that some `ELF` method are staying on the same EL. For example `flatMap` gets a new `ELF` from the closure provided to it. If the `ELF` is on the same EL we do not need to hop; however, we can not guarantee this right now from a type level so we have to stay on the safe side and actually require the `NewValue` to be `Sendable`. # Result This PR makes us more correct from a Sendability perspective but produces warnings for some safe patterns that are currently in use.
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weissi
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Aug 11, 2023
| let eventLoop = self.eventLoop | ||
| return self.flatMap { | ||
| callback($0, eventLoop) | ||
| }.hop(to: self.eventLoop) |
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you can delete the .hop(to:). self.flatMap will return a future on self.eventLoop
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and the previous implementation probably also allocates less, depends on the optimiser a bit. Why not just revert?
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Right. Well this method became a lot easier then :D
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Motivation
With #2496 we fixed a Sendability checking hole by removing the unconditional conformance of
EventLoopFuture/PromisetoSendable. This was the correct thing to do; however, it has the fallout that a couple of methods are now rightly complaining that their values are send across isolation domains.Modification
This PR requires values on some
ELF/Pmethods to beSendablewhen we might potentially transfer the values across isolation domains/ELs. We have to be overly aggressive here because we do not know that someELFmethod are staying on the same EL. For exampleflatMapgets a newELFfrom the closure provided to it. If theELFis on the same EL we do not need to hop; however, we can not guarantee this right now from a type level so we have to stay on the safe side and actually require theNewValueto beSendable.Result
This PR makes us more correct from a Sendability perspective but produces warnings for some safe patterns that are currently in use.