Atomic property in Swift using DispatchQueue and OperationQueue. See blog post for more details: http://www.vadimbulavin.com/atomic-properties/

AtomicPropertyWithDispatchAndOperationsQueues.swift

// MARK: - DispatchQueue

class DispatchQueueAtomicProperty {
    private let queue = DispatchQueue(label: "com.vadimbulavin.DispatchQueueAtomicProperty")
    private var underlyingFoo = 0

    var foo: Int {
        get {
            return queue.sync { underlyingFoo }
        }
        set {
            queue.sync { [weak self] in
                self?.underlyingFoo = newValue
            }
        }
    }
}

// MARK: - OperationsQueue

class OperationsQueueAtomicProperty {
    private let queue: OperationQueue = {
        var q = OperationQueue()
        q.maxConcurrentOperationCount = 1
        return q
    }()
    
    private var underlyingFoo = 0

    var foo: Int {
        get {
            var foo: Int!
            execute(on: queue) { [underlyingFoo] in
                foo = underlyingFoo
            }
            return foo
        }
        set {
            execute(on: queue) { [weak self] in
                self?.underlyingFoo = newValue
            }
        }
    }

    private func execute(on q: OperationQueue, block: @escaping () -> Void) {
        let op = BlockOperation(block: block)
        q.addOperation(op)
        op.waitUntilFinished()
    }
}