Some typos and a few small wording changes#2
Merged
sophiapoirier merged 1 commit intosophiapoirier:closure-isolationfrom Apr 3, 2024
Merged
Some typos and a few small wording changes#2sophiapoirier merged 1 commit intosophiapoirier:closure-isolationfrom
sophiapoirier merged 1 commit intosophiapoirier:closure-isolationfrom
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mattmassicotte
commented
Mar 15, 2024
| ## Introduction | ||
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| This proposal provides the ability to explicitly specify actor-isolation or non-isolation of a closure, as well as providing a parameter attribute to guarantee that a closure parameter inherits the isolation of the context. It makes the isolation inheritance rules more uniform while also making a specific concurrency pattern less restrictive. | ||
| This proposal provides the ability to explicitly specify actor-isolation or non-isolation of a closure, as well as providing a parameter attribute to guarantee that a closure parameter inherits the isolation of the context. It makes the isolation inheritance rules more uniform, helps to better express intention at closure-creation time, and also makes integrating concurrency with non-Sendable types less restrictive. |
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I really appreciate you incorporating my original wording here, but at this point, I think the non-Sendable pattern is much less-impactful than the other changes.
mattmassicotte
commented
Mar 15, 2024
| Explicit annotation has the benefit of disabling inference rules and the potential that they lead to a formal isolation that is not preferred. For example, there are circumstances where it is beneficial to guarantee that a closure is `nonisolated` therefore knowing that its execution will hop off the current actor. Explicit annotation also offers the ability to identify a mismatch of intention, such as a case where the developer expected `nonisolated` but inference landed on actor-isolated, and the closure is mistakenly used in an isolated context. Using explicit annotation, the developer would receive a diagnostic about a `nonisolated` closure being used in an actor-isolated context which helpfully identifies this mismatch of intention. | ||
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| Additionally, there is a difference in how isolation inheritance behaves via the experimental attribute `@_inheritActorContext` (as used by `Task.init`) for isolated parameters vs actor isolation: global actor isolatation is inherited by `Task`'s initializer closure argument, whereas an actor-isolated parameter is not inherited. This makes it challenging to build intuition around how isolation inheritance works. It also makes the concurrency pattern impossible to allow a non-Sendable type to create a new Task that can mutate self. | ||
| Additionally, there is a difference in how isolation inheritance behaves via the experimental attribute `@_inheritActorContext` (as used by `Task.init`) for isolated parameters vs actor isolation: global actor isolation is inherited by `Task`'s initializer closure argument, whereas an actor-isolated parameter is not inherited. This makes it challenging to build intuition around how isolation inheritance works. It also makes it impossible to allow a non-Sendable type to create a new Task that can access self. |
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1 - Typo
2 - just clarify that the problem is worse that just mutating self
3 - simplify wording
mattmassicotte
commented
Mar 15, 2024
| ```swift | ||
| actor A { | ||
| func isolate() { | ||
| nonisolated func isolate() { |
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I was a little confused here, because I think the same is semantically equivalent to just not using an isolated capture at all, isn't it?
I make this function nonisolated to really highlight the new capabilities. But please look at this closely, because I could be wrong!
mattmassicotte
commented
Mar 15, 2024
| ### Isolation inheritance | ||
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| Provide a formal replacement of the experimental parameter attribute `@_inheritActorContext` to resolve its ambiguity with closure isolation. Its replacement `@inheritsIsolation` changes the behavior so that it unconditionally and implicitly captures the isolation context (as opposed to currently in actor-isolated contexts it being conditional on whether you capture an isolated parameter or isolated capture or actor-isolated function, but guaranteed if the context is isolated to a global actor or `nonisolated`). | ||
| Provide a formal replacement of the experimental parameter attribute `@_inheritActorContext` to resolve its ambiguity with closure isolation. Currently, `@_inheritActorContext` actual context capture behavior is conditional on whether you capture an isolated parameter or isolated capture or actor-isolated function, but unconditional if the context is isolated to a global actor or `nonisolated`. Its replacement `@inheritsIsolation` changes the behavior so that it unconditionally and implicitly captures the isolation context. |
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I hope you don't mind this, but I extracted the large parenthesized backstory. I just think the backstory is important!
mattmassicotte
commented
Mar 15, 2024
| ``` | ||
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| While it is technically possible to enqueue work on a remote distributed actor reference, the enqueue on such actor will always immediately crash. Because of that, we err on the side of disallowing such illegal code. [Future directions](#future-directions) discusses how this can be made more powerful when it is known that an actor is local. It is also worth noting the `da.whenLocal { isolated da in ... }` API which allows dynamically recovering an isolated distributed actor reference after it has dynamically been checked for locality. | ||
| While it is technically possible to enqueue work on a remote distributed actor reference, the enqueue on such an actor will always immediately crash. Because of that, we err on the side of disallowing such illegal code. [Future directions](#future-directions) discusses how this can be made more powerful when it is known that an actor is local. It is also worth noting the `da.whenLocal { isolated da in ... }` API which allows dynamically recovering an isolated distributed actor reference after it has dynamically been checked for locality. |
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Tiny typo - missing word.
mattmassicotte
commented
Mar 15, 2024
| { nonisolated in print(nonisolated) } | ||
| ``` | ||
| but with this proposed change, `nonisolated` in this case would instead be interpretted as the contextual keyword specifying the formal isolation of the closure. Such code would then result in a compilation error when trying to use a parameter named `nonisolated`. | ||
| but with this proposed change, `nonisolated` in this case would instead be interpreted as the contextual keyword specifying the formal isolation of the closure. Such code would then result in a compilation error when trying to use a parameter named `nonisolated`. |
sophiapoirier
approved these changes
Apr 3, 2024
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