Swift多线程：使用Thread进行多线程间通讯，协调子线程任务1. Thread的三种建立方式2. Thread的基本使用3. 使用NSCondition实现线程间通讯4. pthread

Thread.detachNewThread {
    print("A new thread,name:\(Thread.current)")
}


//带一个Selector
       Thread.detachNewThreadSelector(#selector(threadPrint), toTarget: self, with: nil)

Thread(block: <#T##() -> Void#>)
Thread(target: <#T##Any#>, selector: <#T##Selector#>, object: <#T##Any?#>)

   let customThread = Thread(target: self, selector: #selector(threadPrint), object: nil)
    customThread.start()

extension NSObject {

    
    open func performSelector(onMainThread aSelector: Selector, with arg: Any?, waitUntilDone wait: Bool, modes array: [String]?)

    open func performSelector(onMainThread aSelector: Selector, with arg: Any?, waitUntilDone wait: Bool)

    
    @available(iOS 2.0, *)
    open func perform(_ aSelector: Selector, on thr: Thread, with arg: Any?, waitUntilDone wait: Bool, modes array: [String]?)

    @available(iOS 2.0, *)
    open func perform(_ aSelector: Selector, on thr: Thread, with arg: Any?, waitUntilDone wait: Bool)

    
    @available(iOS 2.0, *)
    open func performSelector(inBackground aSelector: Selector, with arg: Any?)
}

- 不要在主线程中调用啊，会让UI线程退出的。退出之后看你怎么搞！
- 退出之后，这个线程剩下的所有代码都不会被执行。
- 调用这个方法之前，**一定要注意释放之前由C语言创建的对象**，不然会造成内存泄漏等问题。取消：这个

class ViewController: UIViewController {
    var downImages: Thread?
    var downArticles: Thread?
    
    let imageCondition = NSCondition()
    let articleCondition = NSCondition()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        downImages = Thread(target: self, selector: #selector(downloadImages), object: nil)
        downArticles = Thread(target: self, selector: #selector(downloadArticles), object: nil)
        downImages?.start()
        
    }
    
    @objc private func threadPrint() {
        Thread.sleep(forTimeInterval: 2)
        print("After 2 seconds, I have been performed. I am \(Thread.current)")
    }
    
    @objc fileprivate func downloadImages() {
        for index in 1...5 {
            print("Downloading No.\(index) image.")
            Thread.sleep(forTimeInterval: 1)
            
            if index == 2 {
                //start downArticles.开启下载文章的线程
                downArticles?.start()
                
                //Lock the image thread.加锁，让下载图片的线程进入等待状态
                imageCondition.lock()
                imageCondition.wait()
                imageCondition.unlock()
            }
        }
        print("All images have been completed.")
        
        //Signaling the article when all images completed.
//        等图片都下载完成之后，激活下载文章的进程
        articleCondition.signal()
    }
    
    @objc fileprivate func downloadArticles() {
        for index in 1...5 {
            print("The No.\(index) article will be downloading.")
            Thread.sleep(forTimeInterval: 1)
            if index == 3 {
                //Signaling the image thread, let it continue to down.
                //激活图片的线程，让它继续下载图片
                imageCondition.signal()
                
                //Lock the article thread.加锁，让下载文章的线程进入等待状态
                articleCondition.lock()
                articleCondition.wait()
                articleCondition.unlock()
                
            }
        }
        print("There are 5 articles.")
        
    }
}