4

有人知道如何在 iOS 10 中制作原子布尔值吗？

当前代码：

import UIKit

struct AtomicBoolean {
    fileprivate var val: UInt8 = 0

    /// Sets the value, and returns the previous value.
    /// The test/set is an atomic operation.
    mutating func testAndSet(_ value: Bool) -> Bool {
       if value {
           return OSAtomicTestAndSet(0, &val)
       } else {
           return OSAtomicTestAndClear(0, &val)
       }
    }

    /// Returns the current value of the boolean.
    /// The value may change before this method returns.
    func test() -> Bool {
      return val != 0
    }
}

代码按预期工作，但我不断收到警告：

'OSAtomicTestAndSet' was deprecated in iOS 10.0: Use atomic_fetch_or_explicit(memory_order_relaxed) from <stdatomic.h> instead

我无法让它与 atomic_fetch_or_explicit(memory_order_relaxed) 一起使用。

有谁知道如何将我当前的代码转换为 iOS 10，以消除此警告？

谢谢！

4

3 回答 3

4

更好的方法是避免它......如果你想模仿它只是为了同步对你的 AtomicBoolean 的访问，请使用 GCD 中可用的同步

例如

import PlaygroundSupport
import Foundation
import Dispatch

PlaygroundPage.current.needsIndefiniteExecution = true

let q = DispatchQueue(label: "print")

struct AtomicBoolean {
    private var semaphore = DispatchSemaphore(value: 1)
    private var b: Bool = false
    var val: Bool  {
        get {
            q.async {
                print("try get")
            }
            semaphore.wait()
            let tmp = b
            q.async {
                print("got", tmp)
            }
            semaphore.signal()
            return tmp
        }
        set {
            q.async {
                print("try set", newValue)
            }
            semaphore.wait()
            b = newValue
            q.async {
                print("did", newValue)
            }
            semaphore.signal()
        }
    }

}
var b = AtomicBoolean()

DispatchQueue.concurrentPerform(iterations: 10) { (i) in
    if (i % 4 == 0) {
        _ = b.val
    }
    b.val = (i % 3 == 0)
}

印刷

try get
try set false
try set false
try set true
did false
got false
try get
try set true
did false
try set false
did true
did true
try set true
try set false
got false
try set false
did false
try get
did true
try set true
did false
did false
got false
try set false
did true
did false
于 2017-06-21T21:59:52.243 回答
0

Apple 确认 Bool 值的读取和写入在 Swift 中不是原子操作。

但是有很多方法可以同步。

例子

在某处添加以下全局功能逻辑：

func synchronized<T>(_ lock: AnyObject, _ body: () throws -> T) rethrows -> T {
    objc_sync_enter(lock)
    defer { objc_sync_exit(lock) }
    return try body()
}

并使用如下：

let myLock = NSObject();

// ...

synchronized(myLock) {
    // Something not thread safe here...
}
于 2021-09-29T21:51:09.760 回答
0

你的第一个选择是...

  1. 只需使用普通锁并保护您的价值访问，另一个是......
  2. 使用Swift Atomics

然后你可以说

var value = ManagedAtomic<UInt8>(0)

// Atomic store
value.store(2, ordering: .relaxed)

// Atomic load
value.load(ordering: .relaxed)
于 2021-12-03T11:46:03.420 回答