1.延时器

// 主线程调用
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + 5.0) {
    print("5 秒后输出", Thread.current.isMainThread)
}
// 5 秒后输出 true

2.异步执行回主线程写法

DispatchQueue.global().async {
    print("async do something\(Thread.current)")
    DispatchQueue.main.async {
        print("come back to main thread\(Thread.current)")
    }
}
/*
async do something<NSThread: 0x600002f7e6c0>{number = 3, name = (null)}
come back to main thread<NSThread: 0x600002f27c80>{number = 1, name = main}
*/

3. DispatchGroup(线程组)

let group = DispatchGroup()
// 第一组
group.enter()
AlamofireTools().getAlamofireData(url: "topic/list/jingxuan/1/bs02-iphone-4.6/0-500.json", success: { (json) in
    group.leave()
    print("第一组成功")
}) { (error) in
     group.leave()
    print("第一组失败")
}

// 第二组
group.enter()
AlamofireTools().getAlamofireData(url: "topic/list/jingxuan/1/bs02-iphone-4.6/0-10.json", success: { (json) in
    group.leave()
    print("第二组成功")
}) { (error) in
    group.leave()
    print("第二组失败")
}

// 结束
group.notify(queue: DispatchQueue.main) {
     print("全部执行完成")
}
/*
第二组成功
第一组成功
全部执行完成
*/

4.信号量(DispatchSemaphore)

let semaphore = DispatchSemaphore(value: 1)
let queue = DispatchQueue(label: "L?II")


// 第一组
queue.async {
     semaphore.wait()
    AlamofireTools().getAlamofireData(url: "topic/list/jingxuan/1/bs02-iphone-4.6/0-100.json", success: { (json) in
        semaphore.signal()
        print("第一组成功")
    }) { (error) in
        semaphore.signal()
        print("第一组失败")
    }
}


// 第二组
queue.async {
    semaphore.wait()
    AlamofireTools().getAlamofireData(url: "topic/list/jingxuan/1/bs02-iphone-4.6/0-100000.json", success: { (json) in
        semaphore.signal()
        print("第二组成功")
    }) { (error) in
        semaphore.signal()
        print("第二组失败")
    }
}


// 结束
queue.async {
    semaphore.wait()

    AlamofireTools().getAlamofireData(url: "topic/list/jingxuan/1/bs02-iphone-4.6/0-1.json", success: { (json) in
        semaphore.signal()
        print("全部执行完成")
    }) { (error) in
        semaphore.signal()
        print("全部执行完成")
    }
}
/*
queue.async {
    semaphore.wait()
    DispatchQueue.main.async {
        print("全部执行完成")
        semaphore.signal()
    }
}
*/
/*
第一组成功
第二组成功
全部执行完成
*/