总之，这里给出了更常见的方法，包括返回值或void和throw

import Foundation

extension NSObject {


    func synchronized<T>(lockObj: AnyObject!, closure: () throws -> T) rethrows ->  T
    {
        objc_sync_enter(lockObj)
        defer {
            objc_sync_exit(lockObj)
        }

        return try closure()
    }


}

在Swift4中使用NSLock:

let lock = NSLock()
lock.lock()
if isRunning == true {
        print("Service IS running ==> please wait")
        return
} else {
    print("Service not running")
}
isRunning = true
lock.unlock()

警告 NSLock类使用POSIX线程来实现它的锁定行为。当向NSLock对象发送解锁消息时，必须确保该消息是从发送初始锁定消息的同一个线程发送的。从不同的线程解锁锁可能会导致未定义的行为。

您可以创建propertyWrapper synchronized

这里是NSLock下罩的例子。你可以使用任何你想要的同步GCD, posix_locks等

@propertyWrapper public struct Synchronised<T> {
    private let lock = NSLock()

    private var _wrappedValue: T
    public var wrappedValue: T {
        get {
            lock.lock()
            defer {
                lock.unlock()
            }
            return _wrappedValue
        }
        set {
            lock.lock()
            defer {
                lock.unlock()
            }
            _wrappedValue = newValue
        }
    }

    public init(wrappedValue: T) {
        self._wrappedValue = wrappedValue
    }
}

@Synchronised var example: String = "testing"

基于@drewster的答案

斯威夫特4

在Swift 4中，你可以使用gcd调度队列来锁定资源。

class MyObject {
    private var internalState: Int = 0
    private let internalQueue: DispatchQueue = DispatchQueue(label:"LockingQueue") // Serial by default

    var state: Int {
        get {
            return internalQueue.sync { internalState }
        }

        set (newState) {
            internalQueue.sync { internalState = newState }
        }
    }
} 

使用Swift的属性包装器，这是我现在使用的:

@propertyWrapper public struct NCCSerialized<Wrapped> {
    private let queue = DispatchQueue(label: "com.nuclearcyborg.NCCSerialized_\(UUID().uuidString)")

    private var _wrappedValue: Wrapped
    public var wrappedValue: Wrapped {
        get { queue.sync { _wrappedValue } }
        set { queue.sync { _wrappedValue = newValue } }
    }

    public init(wrappedValue: Wrapped) {
        self._wrappedValue = wrappedValue
    }
}

然后你可以这样做:

@NCCSerialized var foo: Int = 10

or

@NCCSerialized var myData: [SomeStruct] = []

然后像往常一样访问变量。

在现代Swift 5中，具有返回功能:

/**
Makes sure no other thread reenters the closure before the one running has not returned
*/
@discardableResult
public func synchronized<T>(_ lock: AnyObject, closure:() -> T) -> T {
    objc_sync_enter(lock)
    defer { objc_sync_exit(lock) }

    return closure()
}

像这样使用它，以利用返回值功能:

let returnedValue = synchronized(self) { 
     // Your code here
     return yourCode()
}

或者像这样:

synchronized(self) { 
     // Your code here
    yourCode()
}