Swift Concurrency Resources: DevForums tags: Concurrency The Swift Programming Language > Concurrency documentation Migrating to Swift 6 documentation WWDC 2022 Session 110351 Eliminate data races using Swift Concurrency — This ‘sailing on the sea of concurrency’ talk is a great introduction to the fundamentals. WWDC 2021 Session 10134 Explore structured concurrency in Swift — The table that starts rolling out at around 25:45 is really helpful. Swift Async Algorithms package Swift Concurrency Proposal Index DevForum post Why is flow control important? DevForums post Matt Massicotte’s blog Dispatch Resources: DevForums tags: Dispatch Dispatch documentation — Note that the Swift API and C API, while generally aligned, are different in many details. Make sure you select the right language at the top of the page. Dispatch man pages — While the standard Dispatch documentation is good, you can still find some great tidbits in the man pages. See Reading UNIX Manual Pages. Start by reading dispatch in section 3. WWDC 2015 Session 718 Building Responsive and Efficient Apps with GCD [1] WWDC 2017 Session 706 Modernizing Grand Central Dispatch Usage [1] Avoid Dispatch Global Concurrent Queues DevForums post Share and Enjoy — Quinn “The Eskimo!” @ Developer Technical Support @ Apple let myEmail = "eskimo" + "1" + "@" + "apple.com" [1] These videos may or may not be available from Apple. If not, the URL should help you locate other sources of this info.

Hi, In the WWDC25 session Elevate an app with Swift concurrency (timestamps: 8:04 and later), the StickerViewModel is shown annotated with @Observable but not @MainActor. The narration mentions that updates happen on the main thread, but that guarantee is left implicit in the calling code. In Swift 6, though, one of the major benefits is stronger compiler enforcement against data races and isolation rules. If a view model were also annotated with @MainActor, then the compiler could enforce that observable state is only updated on the main actor, preventing accidental background mutations or updates that can cause data races between nonisolated and main actor-isolated uses. Since @Observable already signals that state changes are intended to be observed (and in practice, usually by views), it seems natural that such types should also be main-actor isolated. Otherwise, we’re left with an implicit expectation that updates will always come from the main thread, but without the compiler’s help in enforcing that rule. This also ties into the concept of local reasoning that was emphasized in other Swift 6 talks (e.g. Beyond the basics of structured concurrency). With @MainActor, I can look at a view model and immediately know that all of its state is main-actor isolated. With only @Observable, that guarantee is left out, which feels like it weakens the clarity that Swift 6 is trying to promote. Would it be considered a best practice in Swift 6 to use both @Observable and @MainActor for UI-facing view models? Or is the intention that SwiftUI developers should rely on calling context to ensure main-thread updates, even if that means the compiler cannot enforce isolation? Thanks!

Hi, Are there rules around using Foundation Models: In a background task/session? Concurrently, i.e. a bunch simultaneously using Swift Concurrency? I couldn't find this in the docs (sorry if I missed it) so wondering what's supported and what the best practice is here. In case it matters, my primary platform is Vision Pro (so, M2).

Hello, While watching WWDC25: Code-along: Elevate an app with Swift concurrency at timestamp 25:48, I noticed something in the slide/diagram that might be incorrect. The diagram shows ExtractSticker twice, but based on the code context and spoken explanation, I think it was meant to be ExtractSticker and ExtractColor. Reasoning: The surrounding code and narration describe the use of async let and a Sendable Data object. From the flow, one task extracts a sticker while the other extracts a color, so it seems like the diagram is inconsistent. I do understand that with @concurrent, having two ExtractSticker operations on the same Data is technically possible (with two concurrent process executing their respective ExtractSticker) — but that would be a different meaning than what the talk was describing. Since concurrency is already a subtle and error-prone topic, I thought it was worth pointing this out. If I’m mistaken, I’d love clarification. Otherwise, this could be a small correction to keep things aligned and clearer for everyone. Minor point overall, but Swift 6’s concurrency model is doing a fantastic job at helping us write safer code—so thank you to the team for that! (Attaching screenshots for reference)

I filed the following issue on swiftlang/swift on GitHub (Aug 8th), and a followup the swift.org forums, but not getting any replies. As we near the release of Swift 6.2, I want to know if what I'm seeing below is expected, or if it's another case where the compiler needs a fix. protocol P1: Equatable { } struct S1: P1 { } // Error: Conformance of 'S1' to protocol 'P1' crosses into main actor-isolated code an can cause data races struct S1Workaround: @MainActor P1 { } // OK // Another potential workaround if `Equatable` conformance can be moved to the conforming type. protocol P2 { } struct S2: Equatable, P2 { } // OK There was a prior compiler bug fix which addressed inhereted protocols regarding @MainActor. For Equatable, one still has to use @MainActoreven when the default actor isolation is MainActor. Also affects Hashable and any other protocol inheriting from Equatable.

I have some code which handles doing some computation on a background thread before updating Core Data NSManagedObjects by using the NSManagedObjectContext.perform functions. This code is covered in Sendable warnings in Xcode 26 (beta 6) because my NSManagedObject subclasses (autogenerated) are non-Sendable and NSManagedObjectContext.perform function takes a Sendable closure. But I can't really figure out what I should be doing. I realize this pattern is non-ideal for Swift concurrency, but it's what Core Data demands AFAIK. How do I deal with this? let moc = object.managedObjectContext! try await moc.perform { object.completed = true // Capture of 'object' with non-Sendable type 'MySpecialObject' in a '@Sendable' closure try moc.save() } Thanks in advance for your help!

I have a UIKit app where I've adopted SwiftData and I'm struggling with a crash coming in from some of my users. I'm not able to reproduce it myself and as it only happens to a small fraction of my user base, it seems like a race condition of some sort. This is the assertion message: SwiftData/DefaultStore.swift:453: Fatal error: API Contract Violation: Editors must register their identifiers before invoking operations on this store SwiftData.DefaultStore: 00CF060A-291A-4E79-BEC3-E6A6B20F345E did not. (ID is unique per crash) This is the ModelActor that crashes: @available(iOS 17, *) @ModelActor actor ConsumptionDatabaseStorage: ConsumptionSessionStorage { struct Error: LocalizedError { var errorDescription: String? } private let sortDescriptor = [SortDescriptor(\SDConsumptionSession.startTimeUtc, order: .reverse)] static func createStorage(userId: String) throws -> ConsumptionDatabaseStorage { guard let appGroupContainer = FileManager.default.containerURL(forSecurityApplicationGroupIdentifier: UserDefaults.defaultAppGroupIdentifier) else { throw Error(errorDescription: "Invalid app group container ID") } func createModelContainer(databaseUrl: URL) throws -> ModelContainer { return try ModelContainer(for: SDConsumptionSession.self, SDPriceSegment.self, configurations: ModelConfiguration(url: databaseUrl)) } let databaseUrl = appGroupContainer.appendingPathComponent("\(userId).sqlite") do { return self.init(modelContainer: try createModelContainer(databaseUrl: databaseUrl)) } catch { // Creating the model storage failed. Remove the database file and try again. try? FileManager.default.removeItem(at: databaseUrl) return self.init(modelContainer: try createModelContainer(databaseUrl: databaseUrl)) } } func isStorageEmpty() async -> Bool { (try? self.modelContext.fetchCount(FetchDescriptor<SDConsumptionSession>())) ?? 0 == 0 // <-- Crash here! } func sessionsIn(interval: DateInterval) async throws -> [ConsumptionSession] { let fetchDescriptor = FetchDescriptor(predicate: #Predicate<SDConsumptionSession> { sdSession in if let startDate = sdSession.startTimeUtc { return interval.start <= startDate && interval.end > startDate } else { return false } }, sortBy: self.sortDescriptor) let consumptionSessions = try self.modelContext.fetch(fetchDescriptor) // <-- Crash here! return consumptionSessions.map { ConsumptionSession(swiftDataSession: $0) } } func updateSessions(sessions: [ConsumptionSession]) async throws { if #unavailable(iOS 18) { // Price segments are duplicated if re-inserted so unfortunately we have to delete and reinsert sessions. // On iOS 18, this is enforced by the #Unique macro on SDPriceSegment. let sessionIds = Set(sessions.map(\.id)) try self.modelContext.delete(model: SDConsumptionSession.self, where: #Predicate<SDConsumptionSession> { sessionIds.contains($0.id) }) } for session in sessions { self.modelContext.insert(SDConsumptionSession(consumptionSession: session)) } if self.modelContext.hasChanges { try self.modelContext.save() } } func deleteAllSessions() async { if #available(iOS 18, *) { try? self.modelContainer.erase() } else { self.modelContainer.deleteAllData() } } } The actor conforms to this protocol: protocol ConsumptionSessionStorage { func isStorageEmpty() async -> Bool func hasCreditCardSessions() async -> Bool func sessionsIn(interval: DateInterval) async throws -> [ConsumptionSession] func updateSessions(sessions: [ConsumptionSession]) async throws func deleteAllSessions() async } The crash is coming in from line 30 and 41, in other words, when trying to fetch data from the database. There doesn't seem to be any common trait for the crashes. They occur across iOS versions and device types. Any idea what might cause this?

I'm working with SwiftData and SwiftUI and it's not clear to me if it is good practice to have a @ModelActor directly populate a SwiftUI view. For example when having to combine manual lab results and clinial results from HealthKit. The Clinical lab results are an async operation: @ModelActor actor LabResultsManager { func fetchLabResultsWithHealthKit() async throws -> [LabResultDto] { let manualEntries = try modelContext.fetch(FetchDescriptor<LabResult>()) let clinicalLabs = (try? await HealthKitService.getLabResults()) ?? [] return (manualEntries + clinicalLabs).sorted { $0.date > $1.date }.map { return LabResultDto(from: $0) } } } struct ContentView: View { @State private var labResults: [LabResultDto] = [] var body: some View { List(labResults, id: \.id) { result in VStack(alignment: .leading) { Text(result.testName) Text(result.date, style: .date) } } .task { do { let labManager = LabResultsManager() labResults = try await labManager.fetchLabResultsWithHealthKit() } catch { // Handle error } } } } EDIT: I have a few views that would want to use these labResults so I need an implementation that can be reused. Having to fetch and combine in each view will not be good practice. Can I pass a modelContext to a viewModel?

I'm struggling to convert Swift 5 to Swift 6. As advised in doc, I first turned strict concurrency ON. I got no error. Then, selected swift6… and problems pop up. I have a UIViewController with IBOutlets: eg a TextField. computed var eg duree func using UNNotification: func userNotificationCenter I get the following error in the declaration line of the func userNotificationCenter: Main actor-isolated instance method 'userNotificationCenter(_:didReceive:withCompletionHandler:)' cannot be used to satisfy nonisolated requirement from protocol 'UNUserNotificationCenterDelegate' So, I declared the func as non isolated. This func calls another func func2, which I had also to declare non isolated. Then I get error on the computed var used in func2 Main actor-isolated property 'duree' can not be referenced from a nonisolated context So I declared duree as nonsilated(unsafe). Now comes the tricky part. The computed var references the IBOutlet dureeField if dureeField.text == "X" leading to the error Main actor-isolated property 'dureeField' can not be referenced from a nonisolated context So I finally declared the class as mainActor and the textField as nonisolated @IBOutlet nonisolated(unsafe) weak var dureeField : UITextField! That silences the error (but declaring unsafe means I get no extra robustness with swift6) just to create a new one when calling dureeField.text: Main actor-isolated property 'text' can not be referenced from a nonisolated context Question: how to address properties inside IBOutlets ? I do not see how to declare them non isolated and having to do it on each property of each IBOutlet would be impracticable. The following did work, but will make code very verbose: if MainActor.assumeIsolated({dureeField.text == "X"}) { So I must be missing something.

I have a TVTopShelfContentProvider that implements func loadTopShelfContent() async -&gt; (any TVTopShelfContent)? When running on Xcode 26 b5 I am seeing the following error in swift 6 mode. Non-Sendable type '(any TVTopShelfContent)?' cannot be returned from nonisolated override to caller of superclass instance method 'loadTopShelfContent()' I'm not sure exactly what's changed here as it used to compile just fine but it's unclear now how I can work-around this error or how the API is supposed to be used. The following definition is enough to trigger the error in Swift 6 language mode. import TVServices class ContentProvider: TVTopShelfContentProvider { override func loadTopShelfContent() async -&gt; (any TVTopShelfContent)? { return nil } } I can "fix" it by adding @preconcurrency to the TVServices import but it seems like this API is unusable currently? Or maybe it's user error on my part?

When attempting to compile an existing project with Swift 6, default isolation set to MainActor and approachable concurrency enabled, all awakeFromNib functions lead to the following compile error: "Main actor-isolated instance method 'awakeFromNib()' has different actor isolation from nonisolated overridden declaration" I've seen articles before approachable concurrency stating that one remedy is to wrap code within the function with MainActor.assumeIsolated{ }. However, that no longer addresses the error. One combination of changes that removes the error is doing the following: nonisolated override func awakeFromNib() { super.awakeFromNib() MainActor.assumeIsolated { ... } } Honestly, that's a mess. Long term, we are looking to remove all these functions, but does anyone have a better solution?

I'm running into a weird SwiftUI concurrency issue that only seems to happen on a real device (iOS 18.5 in my case), and not in simulator. I have a NavigationSplitView where the Detail view uses .task(id:_:) to perform some async work upon appearance (in my real-world case, a map snapshot). When running this on a real device, the first execution of the task works as expected. However, any task subsequent executions, even ones for the same id, always start in the Task.isCancelled state. Is there something about .task(id:_:) that I'm misunderstanding, or have I stumbled upon a serious bug here? import SwiftUI struct ContentView: View { var body: some View { TaskBugSplitView() } } struct TestItem: Identifiable, Hashable { var id: Int var name: String } struct TaskBugSplitView: View { @State private var selectedItemIndex: [TestItem].Index? @State private var testItems: [TestItem] = [ TestItem(id: 1, name: "First Item"), TestItem(id: 2, name: "Second Item"), TestItem(id: 3, name: "Third Item"), TestItem(id: 4, name: "Fourth Item"), TestItem(id: 5, name: "Fifth Item") ] var body: some View { NavigationSplitView { List(testItems.indices, id: \.self, selection: $selectedItemIndex) { item in Text(testItems[item].name) } } detail: { if let selectedItemIndex { TaskBugDetailView(item: testItems[selectedItemIndex]) } else { Text("Select an item") .foregroundStyle(.secondary) } } } } struct TaskBugDetailView: View { @State var item: TestItem @State private var taskResult = "Not started" var body: some View { VStack(spacing: 20) { Text("Item: \(item.name)") .font(.title2) Text("Task Result:") .font(.headline) Text(taskResult) .foregroundStyle(taskResult.contains("CANCELLED") ? .red : .primary) Spacer() } .padding() .navigationTitle(item.name) .task(id: item.id) { // BUG: On real devices, Task.isCancelled is true immediately for all tasks // after the first successful one, even though the ID has changed if Task.isCancelled { taskResult = "CANCELLED at start" print("Task cancelled at start for item \(item.id)") return } taskResult = "SUCCESS" print("Task completed successfully for item \(item.id)") } } }

Every time macOS goes to sleep the processes get suspended which is expected. But during the sleep period, all processes keep coming back and they all get a small execution window where they make some n/w requests. Regardless of what power settings i have. It also does not matter whether my app is a daemon or not Is there any way that i can disable this so that when system is in sleep, it stays in suspended, no intermittent execution window? I have tried disabling Wake for network access setting but processes still keep getting intermittent execution window. Is there any way that i can prevent my app from coming back while in sleep. I don't want my app to get execution window, perform some executions and then get suspended not knowing when it will get execution window again?

In my Xcode app, I was attempting to use the #Playground macro to play around with some of the Foundation Model features to see if they would work for my iOS app. However, every time I used a #Playground macro, even if it was empty, it would receive the following error: /var/folders/q2/x5b9x0y161bb2l_0yj1_j6wm0000gn/T/swift-generated-sources/@__swiftmacro_20PlaygroundMacroIssue0022ContentViewswift_tiAIefMX26_0_33_B691877350F20F2DFC040B9E585F4D10Ll0A0fMf_.swift:51:5 Main actor-isolated let '$s20PlaygroundMacroIssue0022ContentViewswift_tiAIefMX26_0_33_B691877350F20F2DFC040B9E585F4D10Ll0A0fMf_23PlaygroundContentRecordfMu_' can not be referenced from a nonisolated context Here are my Xcode and system versions: Mac is running the first public beta of Tahoe. iOS Simulator is running 26.0 dev beta 4. Xcode is Xcode 26 beta 4. So, I went to try to reproduce the error in a blank iOS app project (the error above is the one that I reproduced in that project). Here are the steps that I took. I created a new iOS project in Xcode 26. I went into the ContentView.swift that was created for me and imported the Playgrounds module and created a blank #Playground at the bottom of the file. I then compiled the project and it ran just fine. To try to find out what the issue was, I looked at the concurrency settings. In my real app, Strict Concurrency Checking was set to Complete but was Minimal in my test project. So I went and changed that setting in my real app and it didn't fix anything. Next, I looked at the Swift Version, which turned out to be the culprit. My test app was running Swift 5 whereas the real app was running Swift 6. It seems to have crashed while running Swift 6, not 5. I have trouble understanding what the error is saying. I have tried using the Code Intelligence feature to fix the bug but it hasn't helped. Has anyone here experienced a similar bug? Is there something I can do to fix it or is this an error in Xcode that should be reported? I have attached an iCloud link to my test project if anybody wants to see if they can reproduce the issue: here Thanks!

I'm having trouble dealing with concurrency with the SFAuthorizationPluginView. Does anybody know how this can be solved? https://developer.apple.com/documentation/securityinterface/sfauthorizationpluginview The crux of it is: If I inherit an object as part of an API, and the API is preconcurrency, and thus is nonisolated (but in reality is @MainActor), how do I return a @MainActor GUI element? https://developer.apple.com/documentation/securityinterface/sfauthorizationpluginview/firstresponder() The longer story: I made my view class inherit SFAuthorizationPluginView. The API is preconcurrency (but not marked as preconcurrency) I started using concurrency in my plugin to retrieve data over XPC. (https://developer.apple.com/documentation/xpc/xpcsession + https://developer.apple.com/documentation/swift/withcheckedthrowingcontinuation(isolation:function:_:)) Once I retrieve the data over XPC, I need to post it on GUI, hence I've set my view class as @MainActor in order to do the thread switch. Swift compiler keeps complaining: override func firstResponder() -&gt; NSResponder? { return usernameField } "Main actor-isolated property 'usernameField' can not be referenced from a nonisolated context; this is an error in the Swift 6 language mode" override func firstResponder() -&gt; NSResponder? { MainActor.assumeIsolated { return usernameField } } "Sending 'self' risks causing data races; this is an error in the Swift 6 language mode" I think fundamentally, the API is forcing me to give away a @MainActor variable through a nonisolated function, and there is no way to shut up the compiler. I've tried @preconcurrency and it has no effect as far as I can tell. I've also tried marking the function explicitly as nonisolated. The rest of the API are less problematic, but returning a GUI variable is exceptionally difficult.

AsyncStream { continuation in Task { let response = await getResponse() continuation.yield(response) continuation.finish() } } In this WWDC video https://developer.apple.com/videos/play/wwdc2025/231/ at 8:20 the presenter mentions that if the "Task gets cancelled, the Task inside the function will automatically get cancelled too". The documentation does not mention anything like this. From my own testing on iOS 18.5, this is not true.

I'm encountering a crash on app launch. The crash is observed in iOS version 17.6 but not in iOS version 18.5. The only new notable thing I added to this app version was migrate to store kit 2. Below is the error message from Xcode: Referenced from: &lt;DCC68597-D1F6-32AA-8635-FB975BD853FE&gt; /private/var/containers/Bundle/Application/6FB3DDE4-6AD5-4778-AD8A-896F99E744E8/callbreak.app/callbreak Expected in: &lt;A0C8B407-0ABF-3C28-A54C-FE8B1D3FA7AC&gt; /usr/lib/swift/libswift_Concurrency.dylib Symbol not found: _$sScIsE4next9isolation7ElementQzSgScA_pSgYi_tYa7FailureQzYKFTu Referenced from: &lt;DCC68597-D1F6-32AA-8635-FB975BD853FE&gt; /private/var/containers/Bundle/Application/6FB3DDE4-6AD5-4778-AD8A-896F99E744E8/callbreak.app/callbreak Expected in: &lt;A0C8B407-0ABF-3C28-A54C-FE8B1D3FA7AC&gt; /usr/lib/swift/libswift_Concurrency.dylib dyld config: DYLD_LIBRARY_PATH=/usr/lib/system/introspection DYLD_INSERT_LIBRARIES=/usr/lib/libLogRedirect.dylib:/usr/lib/libBacktraceRecording.dylib:/usr/lib/libMainThreadChecker.dylib:/usr/lib/libRPAC.dylib:/System/Library/PrivateFrameworks/GPUToolsCapture.framework/GPUToolsCapture:/usr/lib/libViewDebuggerSupport.dylib``` and Stack Trace: ```* thread #1, stop reason = signal SIGABRT * frame #0: 0x00000001c73716f8 dyld`__abort_with_payload + 8 frame #1: 0x00000001c737ce34 dyld`abort_with_payload_wrapper_internal + 104 frame #2: 0x00000001c737ce68 dyld`abort_with_payload + 16 frame #3: 0x00000001c7309dd4 dyld`dyld4::halt(char const*, dyld4::StructuredError const*) + 304 frame #4: 0x00000001c73176a8 dyld`dyld4::prepare(...) + 4088 frame #5: 0x00000001c733bef4 dyld`start + 1748``` Note: My app is a Godot App and uses objc static libraries. I am using swift with bridging headers for interoperability. This issue wasn't observed until my last version in which the migration to storekit2 was the only notable change.

Hi, I am experiencing main thread freezes from fetching on Main Actor. Attempting to move the function to a background thread, but whenever I reference the TestModel in a nonisolated context or in another model actor, I get this warning: Main actor-isolated conformance of 'TestModel' to 'PersistentModel' cannot be used in actor-isolated context; this is an error in the Swift 6 language mode Is there a way to do this correctly? Recreation, warning on line 13: class TestModel { var property: Bool = true init() {} } struct SendableTestModel: Sendable { let property: Bool } @ModelActor actor BackgroundActor { func fetch() throws -> [SendableTestModel] { try modelContext.fetch(FetchDescriptor<TestModel>()).map { SendableTestModel(property: $0.property) } } }

Hello, We have been encountering a persistent crash in our application, which is deployed exclusively on iPad devices. The crash occurs in the following code block: let requestHandler = ImageRequestHandler(paddedImage) var request = CoreMLRequest(model: model) request.cropAndScaleAction = .scaleToFit let results = try await requestHandler.perform(request) The client using this code is wrapped inside an actor, following Swift concurrency principles. The issue has been consistently reproduced across multiple iPadOS versions, including: iPad OS - 18.4.0 iPad OS - 18.4.1 iPad OS - 18.5.0 This is the crash log - Crashed: com.apple.VN.detectorSyncTasksQueue.VNCoreMLTransformer 0 libobjc.A.dylib 0x7b98 objc_retain + 16 1 libobjc.A.dylib 0x7b98 objc_retain_x0 + 16 2 libobjc.A.dylib 0xbf18 objc_getProperty + 100 3 Vision 0x326300 -[VNCoreMLModel predictWithCVPixelBuffer:options:error:] + 148 4 Vision 0x3273b0 -[VNCoreMLTransformer processRegionOfInterest:croppedPixelBuffer:options:qosClass:warningRecorder:error:progressHandler:] + 748 5 Vision 0x2ccdcc __119-[VNDetector internalProcessUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:]_block_invoke_5 + 132 6 Vision 0x14600 VNExecuteBlock + 80 7 Vision 0x14580 __76+[VNDetector runSuccessReportingBlockSynchronously:detector:qosClass:error:]_block_invoke + 56 8 libdispatch.dylib 0x6c98 _dispatch_block_sync_invoke + 240 9 libdispatch.dylib 0x1b584 _dispatch_client_callout + 16 10 libdispatch.dylib 0x11728 _dispatch_lane_barrier_sync_invoke_and_complete + 56 11 libdispatch.dylib 0x7fac _dispatch_sync_block_with_privdata + 452 12 Vision 0x14110 -[VNControlledCapacityTasksQueue dispatchSyncByPreservingQueueCapacity:] + 60 13 Vision 0x13ffc +[VNDetector runSuccessReportingBlockSynchronously:detector:qosClass:error:] + 324 14 Vision 0x2ccc80 __119-[VNDetector internalProcessUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:]_block_invoke_4 + 336 15 Vision 0x14600 VNExecuteBlock + 80 16 Vision 0x2cc98c __119-[VNDetector internalProcessUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:]_block_invoke_3 + 256 17 libdispatch.dylib 0x1b584 _dispatch_client_callout + 16 18 libdispatch.dylib 0x6ab0 _dispatch_block_invoke_direct + 284 19 Vision 0x2cc454 -[VNDetector internalProcessUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:] + 632 20 Vision 0x2cd14c __111-[VNDetector processUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:]_block_invoke + 124 21 Vision 0x14600 VNExecuteBlock + 80 22 Vision 0x2ccfbc -[VNDetector processUsingQualityOfServiceClass:options:regionOfInterest:warningRecorder:error:progressHandler:] + 340 23 Vision 0x125410 __swift_memcpy112_8 + 4852 24 libswift_Concurrency.dylib 0x5c134 swift::runJobInEstablishedExecutorContext(swift::Job*) + 292 25 libswift_Concurrency.dylib 0x5d5c8 swift_job_runImpl(swift::Job*, swift::SerialExecutorRef) + 156 26 libdispatch.dylib 0x13db0 _dispatch_root_queue_drain + 364 27 libdispatch.dylib 0x1454c _dispatch_worker_thread2 + 156 28 libsystem_pthread.dylib 0x9d0 _pthread_wqthread + 232 29 libsystem_pthread.dylib 0xaac start_wqthread + 8 We found an issue similar to us - https://developer.apple.com/forums/thread/770771. But the crash logs are quite different, we believe this warrants further investigation to better understand the root cause and potential mitigation strategies. Please let us know if any additional information would help diagnose this issue.

Hi! I configure proxy for webview like DispatchQueue.main.async { self.webView.configuration.websiteDataStore.proxyConfigurations = [proxyConfiguration] } It is fine in iosiOS 17 however, it crashes in iOS 18.3. And the problem seems to be related to the left side of the equation. I tried to call print(self.webView.configuration.websiteDataStore.proxyConfigurations.count) in async block and got the same bad access error. But if stop at that line of code and call po self.webView.configuration.websiteDataStore.proxyConfigurations in debugger it returns 0 elements. Did anyone have the same problem? What may cause the exception?

My experience with Swift 6 strict concurrency so far doesn't match my understanding of implicit MainActor isolation semantics. This is a cross-post from StackOverflow. I will link answers between both forums. TL;DR Build succeeds when testing a struct declared in the test module, but fails when the struct is moved to the main module: Main actor-isolated property … cannot be accessed from outside the actor. Steps to reproduce Open up Xcode 26 beta 2 on macOS 26 (probably also ok on current stables). Create a new Swift app with Swift testing, no storage. Call it WhatTheSwift. Set the Swift Language Version on all three targets to Swift 6. Update the default test file to be this: import Testing @testable import WhatTheSwift struct WhatTheSwiftTests { @Test func example() async throws { let thing = Thing(foo: "bar") #expect(thing.foo == "bar") } } struct Thing { let foo: String } That should build fine, and the tests should pass. Now, move the Thing declaration into its own Thing.swift file in the WhatTheSwift module, and try running the test again. You should see this: Observations Marking the test @MainActor allows the test to pass, suggesting the compiler actually wants to isolate Thing.foo to the main actor. My question Why? And why only when Thing is in a different module?