SwiftData 中的并发编程

func updateItem(_ item: Item, timestamp: Date?) async throws {
    guard let context = item.managedObjectContext else { throw MyError.noContext }
    try await context.perform {
        item.timestamp = timestamp
        try context.save()
    }
}

// view context - main queue concurrency type
let viewContext = container.viewContext
let mainContext = NSManagedObjectContext(concurrencyType: .mainQueueConcurrencyType)

// private context - private queue concurrency type
let privateContext = container.newBackgroundContext()

let privateContext = NSManagedObjectContext(concurrencyType: .privateQueueConcurrencyType)

container.performBackgroundTask{ context in
    ...
}

Task.detached {
    let privateContext = ModelContext(container)
}

// In SwiftUI View
Button("Create New Context"){
    let container = modelContext.container
    Task{
        // Using main queue, not background context
        let privateContext = ModelContext(container)
    }
}

SomeView()
    .task {
        // Using main queue, not background context
        let privateContext = ModelContext(modelContext.container)
    }

@ModelActor
actor DataHandler {}

extension DataHandler {
    func updateItem(_ item: Item, timestamp: Date) throws {
        item.timestamp = timestamp
        try modelContext.save()
    }

    func newItem(timestamp: Date) throws -> Item {
        let item = Item(timestamp: timestamp)
        modelContext.insert(item)
        try modelContext.save()
        return item
    }
}

let handler = DataHandler(modelContainer: container)
let item = try await handler.newItem(timestamp: .now)

Task.detached {
    // Using private queue
    let handler = DataHandler(modelContainer: container)
    let item = try await handler.newItem(timestamp: .now)   
}

actor DataHandler {
    nonisolated let modelExecutor: any SwiftData.ModelExecutor
    nonisolated let modelContainer: SwiftData.ModelContainer
    init(modelContainer: SwiftData.ModelContainer) {
        let modelContext = ModelContext(modelContainer)
        modelExecutor = DefaultSerialModelExecutor(modelContext: modelContext)
        self.modelContainer = modelContainer
    }
}

extension DataHandler: SwiftData.ModelActor {}

// The code below is not generated by ModelActor
public protocol ModelActor : Actor {
  
    /// The ModelContainer for the ModelActor
    /// The container that manages the app’s schema and model storage configuration
    nonisolated var modelContainer: ModelContainer { get }

    /// The executor that coordinates access to the model actor.
    ///
    /// - Important: Don't use the executor to access the model context. Instead, use the
    /// ``context`` property.
    nonisolated var modelExecutor: ModelExecutor { get }

    /// The optimized, unonwned reference to the model actor's executor.
    nonisolated public var unownedExecutor: UnownedSerialExecutor { get }

    /// The context that serializes any code running on the model actor.
    public var modelContext: ModelContext { get }

    /// Returns the model for the specified identifier, downcast to the appropriate class.
    public subscript<T>(id: PersistentIdentifier, as as: T.Type) -> T? where T : PersistentModel { get }
}

import SwiftDataKit

actor DataHandler {
    nonisolated let modelExecutor: any SwiftData.ModelExecutor
    nonisolated let modelContainer: SwiftData.ModelContainer
    init(modelContainer: SwiftData.ModelContainer) {
        let modelContext = ModelContext(modelContainer)
        modelExecutor = DefaultSerialModelExecutor(modelContext: modelContext)
        self.modelContainer = modelContainer
    }
    
    func checkQueueInfo() {
        // Get Actor run queue label
        let actorQueueLabel = DispatchQueue.currentLabel
        print("Actor queue:",actorQueueLabel)
        modelContext.managedObjectContext?.perform {
            // Get context queue label
            let contextQueueLabel = DispatchQueue.currentLabel
            print("Context queue:",contextQueueLabel)
        }
    }
}

extension DataHandler: SwiftData.ModelActor {}

// get current dispatch queue label
extension DispatchQueue {
    static var currentLabel: String {
        return String(validatingUTF8: __dispatch_queue_get_label(nil)) ?? "unknown"
    }
}

Task.detached {
    // create handler in non-main thread
    let handler = DataHandler(modelContainer: container)
    await handler.checkQueueInfo()
}

// Output
Actor queue: NSManagedObjectContext 0x600003903b50
Context queue: NSManagedObjectContext 0x600003903b50

Task { @MainActor in
    // create handler in main thread
    let handler = DataHandler(modelContainer: container)
    await handler.checkQueueInfo()
}

// Output
Actor queue: com.apple.main-thread
Context queue: com.apple.main-thread

extension DataHandler {
    func updateItem(identifier: PersistentIdentifier, timestamp: Date) throws {
        guard let item = self[identifier, as: Item.self] else {
            throw MyError.objectNotExist
        }
        item.timestamp = timestamp
        try modelContext.save()
    }
}

let handler = DataHandler(container:container)
try await handler.updateItem(identifier: item.id, timestamp: .now )

func updateItemInContext(identifier: PersistentIdentifier, timestamp: Date) throws {
    guard let item = modelContext.registeredModel(for: identifier) as Item? else {
        throw MyError.objectNotInContext
    }
    item.timestamp = timestamp
    try modelContext.save()
}

func updateItemInContextAndRowCache(identifier: PersistentIdentifier,timestamp: Date) throws {
    if let item = modelContext.model(for: identifier) as? Item {
        item.timestamp = timestamp
        try modelContext.save()
    }
}

Button("Modify in Wrong Thread") {
    let item = items.first!
    DispatchQueue.global().async {
        print(Thread.current)
        item.timestamp = .now
    }
}

Button("Modify in Wrong Thread") {
    let item = items.first!
    DispatchQueue.global().async {
        item.persistentBackingData.setValue(forKey: \.timestamp, to: Date.now)
    }
}