Swift Concurrency Resources: DevForums tags: Concurrency The Swift Programming Language Concurrency > Concurrency 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. 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.

I'm trying to convert my project to use Swift 6 with Complete Concurrency in Xcode 16 beta 1. The project uses TipKit, but I'm getting compile errors when trying to use the TipKit Parameters feature. Here is an example of the type of error I'm seeing (Note that this code from https://developer.apple.com/documentation/tipkit/highlightingappfeatureswithtipkit): struct ParameterRuleTip: Tip { // Define the app state you want to track. @Parameter static var isLoggedIn: Bool = false Static property '$isLoggedIn' is not concurrency-safe because it is non-isolated global shared mutable state. Is there a new pattern for supporting TipKit Parameters in Swift 6 with Complete Concurrency enabled? There is no obvious suggestion for how to fix this. The latest WWDC 2024 TipKit doesn't appear to have any solution(s).

I suspect this will be a "wait for the next beta" item, but thought I'd throw it out here in case anyone knows of a workaround. Mac app compiling under Xcode 16 beta 1. Trying to get rid of all warning that would stop the adoption of Swift 6 -- Strict Concurrency Checking is set to Complete. I'm down to one warning before I can enable swift 6. SwiftUI.Commands Main actor-isolated static method '_makeCommands(content:inputs:)' cannot be used to satisfy nonisolated protocol requirement; this is an error in the Swift 6 language mode That's because I've added menu commands to the app. It's very easy to reproduce. import SwiftUI @main struct CommandApp: App { var body: some Scene { WindowGroup { ContentView() } .commands { HelpCommand() } } } struct HelpCommand: Commands { var body: some Commands { CommandGroup(replacing: .help) { Button("Help me") { // } } } } The suggested fix is telling me what change I should make ot _makeCommands. At least that is how I'm reading it.

Hi, When using Swift Concurrency blocking tasks like file I/O, GPU work and networking can prevent forward moving progress and have the potential to exhaust the cooperative thread pool and under utilize the CPU. It's been recommended to offload these tasks from the cooperative thread pool. Is my understanding correct that the preferred way to do this is by creating async tasks via Dispatch or OperationQueue? And combining these with Continuations if a return value from the task is required? Or should I always be using Continuations in combination with Dispatch/OperationQueue? There are also Executors but the documentation seems a bit limited on how to use these. The new TaskExecutor is also only available on the latest beta's. My question is basically what is the recommend way to offload a task? Thanks!

Hi, Introducing Swift Concurrency to my Metal app has been a bit challenging as Swift Concurrency is limited by the cooperative thread pool. GPU work is obviously not CPU bound and can block forward moving progress, especially when using waitUntilCompleted on the command buffer. For concurrent render work this has the potential of under utilizing the CPU and even creating dead locks. My question is, what is the Metal's teams general recommendation when it comes to concurrency? It seems to me that Dispatch or OperationQueues are still the preferred way for Metal bound tasks in order to gain maximum performance? To integrate with Swift Concurrency my idea is to use continuations that kick off render jobs via Dispatch or Queues? Would this be the best solution to bridge async tasks with Metal work? Thanks!

I have the following var in an @Observable class: var displayResult: String { if let currentResult = currentResult, let decimalResult = Decimal(string: currentResult) { let result = decimalResult.formatForDisplay() UIAccessibility.post(notification: .announcement, argument: "Current result \(result)") return result } else { return "0" } } The UIAccessiblity.post gives me this warning: Reference to static property 'announcement' is not concurrency-safe because it involves shared mutable state; this is an error in Swift 6 How can I avoid this?

I'm trying to migrate my fairly large application to Swift Concurrency. I've have a class marked as @MainActor that sub-classes a 3rd party abstract class that is not migrated to Swift Concurrency. I get the following error: Main actor-isolated class 'MyClass' has different actor isolation from nonisolated superclass 'OtherAbstractClass'; this is an error in the Swift 6 language mode My class needs to be MainActor as it uses other code that is required to be on the MainActor. I can't see how to suppress this warning, I know as a guarantee that the abstract class will always be on the main thread so I need a way of telling the compiler that when I don't own the 3rd party code. import OtherAbstractModule @MainActor class MyClass: OtherAbstractClass { .... } How can I satisfy the compiler in this case?

I'm starting to work on updating my code for Swift 6. I have a number of pieces of code that look like this: private func updateModel() async throws { try await context.perform { [weak self] in // do some work } } After turning on strict concurrency checking, I get warnings on blocks like that saying "Sending 'self.context' risks causing data races; this is an error in the Swift 6 language mode." What's the best way for me to update this Core Data code to work with Swift 6?

I've just tried to update a project that uses SwiftData to Swift 6 using Xcode 16 beta 1, and it's not working due to missing Sendable conformance on a couple of types (MigrationStage and Schema.Version): struct LocationsMigrationPlan: SchemaMigrationPlan { static let schemas: [VersionedSchema.Type] = [LocationsVersionedSchema.self] static let stages: [MigrationStage] = [] } struct LocationsVersionedSchema: VersionedSchema { static let models: [any PersistentModel.Type] = [ Location.self ] static let versionIdentifier = Schema.Version(1, 0, 0) } This code results in the following errors: error: static property 'stages' is not concurrency-safe because non-'Sendable' type '[MigrationStage]' may have shared mutable state static let stages: [MigrationStage] = [] ^ error: static property 'versionIdentifier' is not concurrency-safe because non-'Sendable' type 'Schema.Version' may have shared mutable state static let versionIdentifier = Schema.Version(1, 0, 0) ^ Am I missing something, or is this a bug in the current seed? I've filed this as FB13862584.

I have a Safari Web Extension for visionOS that reads from UIDevice.current.systemVersion in order to provide the OS version number back to the JavaScript context utilizing beginRequest(with:). When switching my project to use Swift 6, I received this obscure error: Main actor-isolated class property 'current' can not be referenced from a non-isolated context Class property declared here (UIKit.UIDevice) Add '@MainActor' to make instance method 'beginRequest(with:)' part of global actor 'MainActor' Adding @MainActor causes another issue (Main actor-isolated instance method 'beginRequest(with:)' cannot be used to satisfy nonisolated protocol requirement) which suggests adding @preconcurrency to NSExtensionRequestHandling which then breaks at Non-sendable type 'NSExtensionContext' in parameter of the protocol requirement satisfied by main actor-isolated instance method 'beginRequest(with:)' cannot cross actor boundary. What's the proper solution here? Here's a simplified snippet of my code: class SafariWebExtensionHandler: NSObject, NSExtensionRequestHandling { func beginRequest(with context: NSExtensionContext) { // ... var systemVersionNumber = "" systemVersionNumber = UIDevice.current.systemVersion // ... } }

How are SwiftUI Shapes supposed to work with Swift 6? Shape conforms to View which uses @MainActor but the path function and animatableData are both nonisolated. How can they access animatable properties that have to be a var on the main actor? Below is a simple Shape that will show these warnings: struct SimpleShape: Shape { var width: Double var animatableData: Double { get { width } set { width = newValue } } func path(in rect: CGRect) -> Path { var path = Path() let width = self.width path.addRect(.init(origin: rect.origin, size: .init(width: width, height: rect.height))) return path } }

Attaching several crash traces: 2024-02-29_22-48-33.6864_-0600-3f948243e21b4c68d77a38d9cf1cecfdfe2c1565.crash 2024-03-04_15-00-02.9335_-0600-75000cd5acd63ba1434f2ffb3648b97259dddb88.crash 2024-03-05_08-55-47.2097_-0500-f682b25663107ad46f091d65f402f2be31f3f3c6.crash 2024-03-11_08-09-00.4057_-0400-e37d1a635d51afbb67ac38b42dd79c1718a408e8.crash 2024-03-15_16-20-22.6446_-0600-d4ebccf455e8305038ca564a39a5661a1dce6231.crash The final code: - (NSObject*)objectAtIndex:(NSUInteger)index { if (index < self.count) { return [self.embeddedArray objectAtIndex:index]; } else { [PNDErrorReporting reportError:PNDErrorReasonTypeSafeCollectionCrashPrevented message:@"Error msg"]; return nil; } } We subclass NSMutableArray to prevent potential crashes. but we encounter a new crash in our sdk for one of the clients. Also we noticed the stack trace skipped one of the frames (stack calls) in the crash report, in which cases the stack trace wont be identical to the actual code (beside inline)?

If I try to compile the following, I get a compilation error: import Foundation func isolatedPrint<A : Actor>(on actor: isolated A) { print("hello") } Task{ @MainActor in isolatedPrint(on: MainActor.shared) } The error: toto.swift:9:2: error: expression is 'async' but is not marked with 'await' isolatedPrint(on: MainActor.shared) ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ await toto.swift:9:2: note: calls to global function 'isolatedPrint(on:)' from outside of its actor context are implicitly asynchronous isolatedPrint(on: MainActor.shared) ^ I don’t understand why the compiler does not detect the function is called on the MainActor via the actor parameter.

So our back end manages tokens in a strange way. Whenever we try to request a new access token using our refresh token, it invalidates our old refresh token and returns us with a new access + refresh token. The problem with this is that multiple concurrent network requests can see that a user's access token has expired and try to get a new access token, potentially causing us to get a 401 unauthorized error. Is there any way with structured/unstructured concurrency to ensure that our method for grabbing the access token can only at max be run once at a time? Im assuming the only realistic way would be to do something like this: @MyGlobalActor private var tokenTask: Task<String, any Error>? @MyGlobalActor func getAccessToken() async await -> String { if let tokenTask { return try await tokenTask.value } self.tokenTask = Task<String, any Error> { // refresh access token } let token = try await self.tokenTask!.value self.tokenTask = nil return token }

I've been studying the AVCam example and notice that everything pertaining to state transitions for the capture session is performed on a dedicated DispatchQueue. My question is this: Can I use an actor instead?

Two structs from the AppIntents framework should be made Sendable: DisplayRepresentation and IntentDescription.

How can an app obtain the valid range for setting thread_time_constraint_policy_data_t for thread_policy_set()?

Hi, I'm trying to implement a type conforming to WKScriptMessageHandlerWithReply while having Swift's strict concurrency checking enabled. It's not been fun. The protocol contains the following method (there's also one with a callback, but we're in 2024): func userContentController( controller: WKUserContentController, didReceive message: WKScriptMessage ) async -> (Any?, String?) WKScriptMessage's properties like body must be accessed on the main thread. But since WKScriptMessageHandlerWithReply is not @MainActor, neither can this method be so marked (same for the conforming type). At the same time WKScriptMessage is not Sendable, so I can't handle it in Task { @MainActor in this method, because that leads to Capture of 'message' with non-sendable type 'WKScriptMessage' in a `@Sendable` closure That leaves me with @preconcurrency import - is that the way to go? Should I file a feedback for this or is it somehow working as intended?

This is a bug I have been trying to identify and fix for more than 3 weeks. This bug mostly happens in production. The stack trace doesn't help that much, because it looks like the app is crashing due to some SwiftUI internal methods. I tried everything in my power to debug and find this bug, still nothing. Due to the lack of 100% reproducibility, it made me think that this bug is either memory-pressure related or Swift concurrency related. When does it happen: This bug happens when presenting a SwiftUI modal (UIViewControllerRepresentable)[A] which in terms presents a UIHostingController modal[B] which then presents a modally a SwiftUI sheet [C] The bug happens somewhere around staying in [C] or after dismissing it. Context: The app lifecycle is SwiftUI. The main SwiftUI screen in the app body is a UIViewControllerRepresentable containing a UISplitViewController. Here is a screenshot from the crash log in Xcode. Anyone facing a similar issue?

When I build app on Xcode 15.3 with SWIFT_STRICT_CONCURRENCY=complete, there are some warning. Almost warning can be fixed, but not the TipKit code. Here is the example. Are there any good way to solve it?

Is the timeout for session-level authentication challenge handling documented somewhere? For example, if I get the urlSession(_:didReceive:) callback for server trust authentication, how long do I have to invoke the completion handler (or return from the callback if using Swift Concurrency)? Or is this completely dependent on the server's settings?