Crashes: suspend resume partial function

Question

diegoreymendez OP

Created Jun ’23

Replies 1

Boosts 0

Participants 2

After changing our main method to become async, with a logic that looks like the following:

    static func main() async throws {
        // A special startup case that does something in the background and kills the app
        if someCondition {
            try await someAsyncCode()
            exit(0)
        }

        _ = NSApplicationMain(CommandLine.argc, CommandLine.unsafeArgv)
    }

we started seeing several crashes that start like this:

... etc
30	AppKit	_DPSNextEvent
31	AppKit	-[NSApplication(NSEvent) _nextEventMatchingEventMask:untilDate:inMode:dequeue:]
32	AppKit	-[NSApplication run]
33	AppKit	NSApplicationMain
34	MyApp	(1) suspend resume partial function for static AppMain.main() (<compiler-generated>:0)
35	MyApp
[crash.txt](https://developer.apple.com/forums/content/attachment/33f37f09-32be-465b-a2e2-7312fab10597)
	(1) await resume partial function for specialized thunk for @escaping @convention(thin) @async () -> () (<compiler-generated>:0)
36	libswift_Concurrency.dylib	completeTaskAndRelease(swift::AsyncContext*, swift::SwiftError*)

I realize there's not a lot of detail and I'm willing to expand on the code and the errors if needed, but I'm wondering if anyone has seen this type of issue after making their main method async.

Boost

Answer 1

DTS Engineer OP

Apple

Jun ’23

Accepted Answer

After changing our main method to become async

Gosh, that seems like a bad idea. NSApplicationMain was not designed to be called from an async function. Try something like this instead:

import Cocoa

func main() {
    if UserDefaults.standard.bool(forKey: "RunInSpecialMode") {
        Task {
            for _ in 0..<3 {
                print("sleep")
                fflush(stdout)
                try? await Task.sleep(for: .seconds(1))
            }
            print("done")
            fflush(stdout)
            exit(0)
        }
        dispatchMain()
    }
    
    _ = NSApplicationMain(CommandLine.argc, CommandLine.unsafeArgv)
}

main()

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