Atomic bool flag in Swift 3

class Request {
    // DTO that can be accessed from different threads

    // Note: this is faster/better/approved by Apple instead of @synchronized and
    // other constructs (even tho' its a bit more verbose).  DispatchQueue by
    // default is Serial so this synchronizes accesses.
    private var requestStateQueue = DispatchQueue(label: "requestStateQueue")
    private var _cancelled = false
    /** Set to true to cancel this request - atomic/threadsafe */
    var cancelled: Bool {
        get {
            var result = false
            requestStateQueue.sync {
                result = _cancelled
            }
            return result
        }
        set {
            requestStateQueue.sync {
                _cancelled = newValue
            }
        }
    }
}