Swift non actor isolated closures-CodePudding

Do escaping closure that are passed to actor method inherit actor isolation? Or they are non isolated?

For instance:

actor MyActor {
   func method(_ closure: @escaping () async -> Void) {
      await closure()
   }
}

With what isolation will closure be created? In my simple test, seems that closure inherit it's context isolation on allocation

actor MyActor {
   func method(_ closure: @escaping () async -> Void) async {
       print("in actor method: ", Thread.current)
       await closure()
       print("in actor method: ", Thread.current)
   }
}

func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

        let actor = MyActor()
        Task {
            print("in task closure: ", Thread.current)
            await actor.method {
                print("in actor closure: ", Thread.current)
                try? await Task.sleep(nanoseconds: 1_000_000_000)
                print("in actor closure: ", Thread.current)
            }
            print("in task closure: ", Thread.current)
        }
        
        return true
}

Outputs:

in task closure:  <_NSMainThread: 0x283604380>{number = 1, name = main}
in actor method:  <NSThread: 0x283654400>{number = 5, name = (null)}
in actor closure:  <_NSMainThread: 0x283604380>{number = 1, name = main}
in actor closure:  <_NSMainThread: 0x283604380>{number = 1, name = main}
in actor method:  <NSThread: 0x283654400>{number = 5, name = (null)}
in task closure:  <_NSMainThread: 0x283604380>{number = 1, name = main}

I know that it's it proper proof of hypothesis, therefore I'm asking: Is there are any proposals or statements, which describe what isolation async closure do get?

CodePudding user response：

Yes, the closure will use the same actor context from which it was formed (the main actor in this example):

As SE-0306 says

A closure that is not @Sendable cannot escape the concurrency domain in which it was formed. Therefore, such a closure will be actor-isolated if it is formed within an actor-isolated context.