swift_concurrency

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Swift Concurrency

Swift并发编程

This skill covers Swift's modern concurrency features from Swift 5.5 through Swift 6, including async/await, structured concurrency, actors, and Swift 6's strict data-race safety.

本技能涵盖了Swift 5.5到Swift 6的现代并发特性，包括async/await、结构化并发、Actor以及Swift 6的严格数据竞争安全机制。

Overview

概述

Swift's modern concurrency model provides a safer, more intuitive way to write asynchronous code. Swift 6 takes this further with compile-time data-race safety, turning potential concurrency bugs into compiler errors.

Swift的现代并发模型提供了一种更安全、更直观的异步代码编写方式。Swift 6更进一步，引入了编译期数据竞争安全机制，将潜在的并发bug转化为编译错误。

Available References

可用参考资料

Swift 6 & Strict Concurrency

Swift 6 & 严格并发

Swift 6 Strict Mode - Complete concurrency checking, data race prevention
Sendable Protocol - Sendable conformance, @Sendable closures, thread safety
Isolation & Actors - @MainActor, global actors, region-based isolation

Swift 6严格模式 - 完整并发检查、数据竞争预防
Sendable协议 - Sendable合规性、@Sendable闭包、线程安全
隔离机制与Actor - @MainActor、全局Actor、基于区域的隔离

Core Concurrency

核心并发特性

Async/Await - Asynchronous functions, Task, TaskGroup, Actor basics

Async/Await - 异步函数、Task、TaskGroup、Actor基础

Swift 6 Highlights

Swift 6核心亮点

Strict Concurrency by Default

默认启用严格并发

Swift 6 enforces data-race safety at compile time:

swift

// ❌ Compile-time error in Swift 6
var globalCounter = 0

func increment() {
    globalCounter += 1  // Error: concurrent access
}

// ✅ Safe with actor isolation
actor Counter {
    private var value = 0
    func increment() { value += 1 }
}

Swift 6在编译期强制实施数据竞争安全：

swift

// ❌ Swift 6中会触发编译错误
var globalCounter = 0

func increment() {
    globalCounter += 1  // 错误：并发访问
}

// ✅ 用Actor隔离实现安全访问
actor Counter {
    private var value = 0
    func increment() { value += 1 }
}

Sendable Protocol

Sendable协议

Mark types safe to share across concurrency boundaries:

swift

struct User: Sendable {
    let id: Int
    let name: String
}

@Sendable func process() async {
    // Captures must be Sendable
}

标记可在并发边界安全共享的类型：

swift

struct User: Sendable {
    let id: Int
    let name: String
}

@Sendable func process() async {
    // 捕获的变量必须符合Sendable
}

MainActor & Global Actors

MainActor与全局Actor

swift

@MainActor
class ViewModel: ObservableObject {
    @Published var items = [Item]()
}

@globalActor
actor DatabaseActor {
    static let shared = DatabaseActor()
    private init() {}
}

swift

@MainActor
class ViewModel: ObservableObject {
    @Published var items = [Item]()
}

@globalActor
actor DatabaseActor {
    static let shared = DatabaseActor()
    private init() {}
}

Quick Reference

快速参考

Async/Await Basics

Async/Await基础

swift

func fetchData() async throws -> Data {
    let (data, _) = try await URLSession.shared.data(from: url)
    return data
}

swift

func fetchData() async throws -> Data {
    let (data, _) = try await URLSession.shared.data(from: url)
    return data
}

Swift 6 Migration Checklist

Swift 6迁移检查清单

Running Async Code

运行异步代码

swift

// Fire-and-forget
Task {
    let result = await asyncOperation()
}

// With priority
Task(priority: .background) {
    await heavyComputation()
}

// With cancellation
let task = Task {
    try await longRunningOperation()
}
task.cancel()

swift

// 即发即弃
Task {
    let result = await asyncOperation()
}

// 带优先级
Task(priority: .background) {
    await heavyComputation()
}

// 支持取消
let task = Task {
    try await longRunningOperation()
}
task.cancel()

Concurrent Operations

并发操作

swift

// Async let (parallel await)
async let task1 = fetchUser()
async let task2 = fetchSettings()
let (user, settings) = try await (task1, task2)

// TaskGroup
try await withThrowingTaskGroup(of: Item.self) { group in
    for id in ids {
        group.addTask { try await fetchItem(id: id) }
    }
    return try await group.reduce(into: []) { $0.append($1) }
}

swift

// Async let（并行等待）
async let task1 = fetchUser()
async let task2 = fetchSettings()
let (user, settings) = try await (task1, task2)

// TaskGroup
try await withThrowingTaskGroup(of: Item.self) { group in
    for id in ids {
        group.addTask { try await fetchItem(id: id) }
    }
    return try await group.reduce(into: []) { $0.append($1) }
}

Actor Thread Safety

Actor线程安全

swift

actor BankAccount {
    private var balance: Double = 0
    
    func deposit(_ amount: Double) {
        balance += amount
    }
    
    func getBalance() -> Double {
        return balance
    }
}

let account = BankAccount()
await account.deposit(100)

swift

actor BankAccount {
    private var balance: Double = 0
    
    func deposit(_ amount: Double) {
        balance += amount
    }
    
    func getBalance() -> Double {
        return balance
    }
}

let account = BankAccount()
await account.deposit(100)

Isolation Boundaries

隔离边界

swift

// Crossing isolation boundaries
@MainActor
func updateUI() async {
    // On main thread
    let data = await fetchData()  // Switch to non-isolated
    label.text = data  // Back to main thread
}

// Region transfer
func process() async {
    let data = Data()  // Disconnected
    await save(data)   // Transfer to actor
    // ❌ Can't use data here anymore
}

swift

// 跨越隔离边界
@MainActor
func updateUI() async {
    // 处于主线程
    let data = await fetchData()  // 切换到非隔离环境
    label.text = data  // 回到主线程
}

// 区域转移
func process() async {
    let data = Data()  // 无关联隔离
    await save(data)   // 转移到Actor环境
    // ❌ 此处无法再使用data
}

Swift 6 vs Swift 5.x

Swift 6与Swift 5.x对比

Feature	Swift 5.x	Swift 6
Concurrency checking	Warnings	Errors
Data race safety	Runtime	Compile-time
Sendable enforcement	Opt-in	Required
Global variable safety	Warning	Error
Strict mode	Experimental	Default

特性	Swift 5.x	Swift 6
并发检查	警告	错误
数据竞争安全	运行时	编译期
Sendable强制	可选启用	必填
全局变量安全	警告	错误
严格模式	实验性	默认

Best Practices

最佳实践

Swift 6 Best Practices

Swift 6最佳实践

Enable Swift 6 mode early - Start migration now
Use actors for shared state - Default to actors over locks
Design Sendable types - Make types Sendable from the start
Isolate UI with @MainActor - All UI code on main thread
Respect isolation regions - Don't use values after transfer
Leverage compile-time safety - Let compiler catch data races
Create domain actors - Custom global actors for heavy work

尽早启用Swift 6模式 - 现在就开始迁移
用Actor管理共享状态 - 优先使用Actor而非锁
设计Sendable类型 - 从一开始就让类型支持Sendable
用@MainActor隔离UI代码 - 所有UI代码在主线程执行
遵守隔离区域规则 - 转移后不再使用原数据
利用编译期安全 - 让编译器捕获数据竞争问题
创建领域Actor - 为繁重工作自定义全局Actor

General Concurrency

通用并发最佳实践

Prefer async/await - Over completion handlers
Use structured concurrency - Clear task hierarchies
Handle cancellation - Check Task.isCancelled
Use value types - Immutable data is thread-safe
Avoid shared mutable state - Or protect with actors

优先使用async/await - 替代完成处理闭包
使用结构化并发 - 清晰的任务层级
处理取消操作 - 检查Task.isCancelled
使用值类型 - 不可变数据天生线程安全
避免共享可变状态 - 或用Actor保护

Migration from Completion Handlers

从完成处理闭包迁移

swift

// Before (Swift 5)
func fetchUser(completion: @escaping (Result<User, Error>) -> Void) {
    URLSession.shared.dataTask(with: url) { data, response, error in
        // Handle result
        completion(result)
    }.resume()
}

// After (Swift 6)
func fetchUser() async throws -> User {
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode(User.self, from: data)
}

swift

// 之前（Swift 5）
func fetchUser(completion: @escaping (Result<User, Error>) -> Void) {
    URLSession.shared.dataTask(with: url) { data, response, error in
        // 处理结果
        completion(result)
    }.resume()
}

// 之后（Swift 6）
func fetchUser() async throws -> User {
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode(User.self, from: data)
}

Common Swift 6 Errors

Swift 6常见错误

Error	Quick Fix
Concurrent access to global	Wrap in actor
Non-Sendable in @Sendable	Make type Sendable
Actor isolation violation	Add await or change isolation
Use after transfer	Use before transfer or copy value
Main actor isolation	Add @MainActor annotation

错误	快速修复方案
全局变量并发访问	用Actor封装
@Sendable中存在非Sendable类型	让类型支持Sendable
违反Actor隔离规则	添加await或修改隔离设置
转移后使用数据	在转移前使用或复制数据
主线程Actor隔离问题	添加@MainActor注解

Resources

资源链接

Swift Evolution: https://github.com/apple/swift-evolution
SE-0412: Strict concurrency for global variables
SE-0471: SerialExecutor isolation checking
SE-0430: Sending parameters
SE-0414: Region-based isolation
Apple Docs: https://developer.apple.com/documentation/swift/concurrency
SwiftZilla: https://swiftzilla.dev

Swift Evolution: https://github.com/apple/swift-evolution
SE-0412: 全局变量的严格并发
SE-0471: 串行执行器隔离检查
SE-0430: 参数传递
SE-0414: 基于区域的隔离
Apple Docs: https://developer.apple.com/documentation/swift/concurrency
SwiftZilla: https://swiftzilla.dev

swift_concurrency

Original

Translation

Swift Concurrency

Swift并发编程

Overview

概述

Available References

可用参考资料

Swift 6 & Strict Concurrency

Swift 6 & 严格并发

Core Concurrency

核心并发特性

Swift 6 Highlights

Swift 6核心亮点

Strict Concurrency by Default

默认启用严格并发

Sendable Protocol

Sendable协议

MainActor & Global Actors

MainActor与全局Actor

Quick Reference

快速参考

Async/Await Basics

Async/Await基础

Swift 6 Migration Checklist

Swift 6迁移检查清单

Running Async Code

运行异步代码

Concurrent Operations

并发操作

Actor Thread Safety

Actor线程安全

Isolation Boundaries

隔离边界

Swift 6 vs Swift 5.x

Swift 6与Swift 5.x对比

Best Practices

最佳实践

Swift 6 Best Practices

Swift 6最佳实践

General Concurrency

通用并发最佳实践

Migration from Completion Handlers

从完成处理闭包迁移

Common Swift 6 Errors

Swift 6常见错误

Resources

资源链接

For More Information

更多信息