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Martin Hope
user2828120
Asked: 2025-04-07 20:50:54 +0800 CST
  • 5

有一个用于读写字典数据的数据存储。我使用了一个全局 Actor，它可以保证操作的串行执行。

代码示例：

@globalActor
struct DataStorageActor {
    actor ActorType { }
    static let shared: ActorType = ActorType()
}

@DataStorageActor
class CustomDataStorage {
    private var storage: [String: String] = [:]
    
    func write(key: String, value: String) async throws {
        print("\(Date()): Write started")
        try await Task.sleep(nanoseconds: 5_000_000_000)
        storage[key] = value
        print("\(Date()): Write completed for key: \(key)")
    }
    
    func read(key: String) async throws -> String? {
        print("\(Date()): Read started")
        let value = storage[key]
        print("\(Date()): Read completed for key: \(key)")
        return value
    }
}

并编写了一个单元测试：

    @Test(arguments: ["Very long string"])
    func testSerialExecution(input: String) async throws {
        let storage = CustomDataStorage()

        let task1 = Task {
            try await storage.write(key: "test", value: input)
        }

        let task2 = Task {
            try await Task.sleep(nanoseconds: 2_000_000_000)
            
            let value = try await storage.read(key: "test")
            print("\(Date()): Received value: \(value ?? "nil")")
            
            return value
        }
        
        print("wait task 1")
        _ = try await task1.value
        
        print("wait task 2")
        let value: String? = try await task2.value
        
        print("check result")
        #expect(value == input)
    }
  1. 在一个单独的线程中，我启动一个长写入操作（5秒）
  2. 在单独的线程中，我启动了延迟 2 秒的读取操作
  3. 我希望读取操作等待写入操作完成

但读取操作是并行运行的，记录如下：

wait task 1
2025-04-07 12:43:03 +0000: Write started
2025-04-07 12:43:05 +0000: Read started
2025-04-07 12:43:05 +0000: Read completed for key: test
2025-04-07 12:43:05 +0000: Received value: nil
2025-04-07 12:43:08 +0000: Write completed for key: test
wait task 2
check result

为什么它会这样工作？

swift