iOS-Swift 信号量

let semaphore = DispatchSemaphore(value: 1)
queue1.async {
    semaphore.wait()
    user.setName("1")
    print(user.name)
    semaphore.signal()
}
queue2.async {
    semaphore.wait()
    user.setName("2")
    print(user.name)
    semaphore.signal()
}