1. 概述

執行緒是非常有用的，當執行一個比較耗時的操作，但是又不想影響到主執行緒的時候，這個時候就需要多執行緒了，從而提高應用程式的效能，增強使用者體驗。
本篇文章將講述iOS多執行緒中的一種Thread，下面來具體看一下。

作為一個開發者，有一個學習的氛圍跟一個交流圈子特別重要，這是一個我的iOS交流群：196800191，加群密碼：112233，不管你是小白還是大牛歡迎入駐 ，分享BAT,阿里面試題、面試經驗，討論技術， 大家一起交流學習成長！

2. Thread的建立

	@available(iOS 2.0, *)
    public convenience init(target: Any, selector: Selector, object argument: Any?)

    @available(iOS 10.0, *)
    public convenience init(block: @escaping () -> Void)

	@available(iOS 10.0, *)
    open class func detachNewThread(_ block: @escaping () -> Void)

    open class func detachNewThreadSelector(_ selector: Selector, toTarget target: Any, with argument: Any?)
 

上面的方法中，前兩個是物件的初始化方法，返回一個Thread物件，而後兩個則是類方法，直接開啟了一個子執行緒。

下面看一組測試：

	func createThread() {
        let thread1 = Thread(target: self, selector: #selector(threadMethod1), object: nil)
        let thread2 = Thread {
            print("thread2 \(Thread.current)")
        }
        thread1.start()
        thread2.start()
        
        Thread.detachNewThreadSelector(#selector(threadMethod3), toTarget: self, with: nil)
        Thread.detachNewThread {
            print("thread4 \(Thread.current)")
        }
    }
    @objc func threadMethod1() {
        print("thread1 \(Thread.current)")
    }
    @objc func threadMethod3() {
        print("thread3 \(Thread.current)")
    }
 

執行後得到：

thread4 <NSThread: 0x600002284600>{number = 9, name = (null)}
thread2 <NSThread: 0x600002284540>{number = 7, name = (null)}
thread1 <NSThread: 0x600002284500>{number = 6, name = (null)}
thread3 <NSThread: 0x600002284580>{number = 8, name = (null)}

通過初始化物件得到的Thread物件，需要呼叫start()方法來開啟子執行緒，即將該子執行緒設定為就緒的狀態，等待CPU的排程。
而通過類方法開闢的兩個子執行緒，不返回Thread物件，建立後即就緒狀態，無需start()方法。

3. Thread常用屬性及方法

常見屬性列表：

常見類方法及例項方法列表：

4. Thread常用屬性及方法示例

override func viewDidLoad() {
        super.viewDidLoad()
        // 設定主執行緒名稱
        Thread.main.name = "MainThread"
        threadTestDemo()
    }
    
    func threadTestDemo() {
        // 建立子執行緒
        myThread = Thread(target: self, selector: #selector(myThreadMethod), object: nil)
        // 設定子執行緒名稱
        myThread?.name = "MyThread"
        // 設定子執行緒優先順序
        myThread?.threadPriority = 1.0
        // 開啟子執行緒
        myThread?.start()
        // 主執行緒阻塞3秒
        Thread.sleep(forTimeInterval: 3)
        // 列印子執行緒執行狀態
        if let thread = myThread {
            print("3 seconds later, myThread is executing :  \(thread.isExecuting)")
            print("3 seconds later, myThread is finished :  \(thread.isFinished)")
        }
    }
    // 子執行緒方法
    @objc func myThreadMethod() {
        // 列印主執行緒
        print("Main thread is :  \(Thread.main)")
        // 列印當前執行緒
        print("Current thread is :  \(Thread.current)")
        // 判斷當前執行緒是否是主執行緒
        print("Current thread is main thread :  \(Thread.isMainThread)")

        if let thread = myThread {
            // 列印子執行緒名稱
            print("myThread name is :  \(String(describing: thread.name))")
            // 列印子執行緒優先順序
            print("myThread priority is :  \(thread.threadPriority)")
            // 列印子執行緒是否是主執行緒
            print("myThread is main thread :  \(thread.isMainThread)")
            // 子執行緒是否正在執行
            print("myThread is executing :  \(thread.isExecuting)")
            // 子執行緒是否標記取消
            print("myThread is cancelled :  \(thread.isCancelled)")
            // 子執行緒是否已經結束。
            print("myThread is finished :  \(thread.isFinished)")
        }
        /*
        // 在子執行緒中新增一個定時器
        Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { (timer) in
            print("Timer is running")
        }
        // 預設子執行緒的runloop是不開啟的，如果不開啟，timer無法執行，所以這裡需要手動開啟。
        RunLoop.current.run()
        */
    }

上面子執行緒方法中註釋了Timer的方法，其執行結果如下：

Main thread is :  <NSThread: 0x600000d80400>{number = 1, name = MainThread}
Current thread is :  <NSThread: 0x600000dcd040>{number = 7, name = MyThread}
Current thread is main thread :  false
myThread name is :  Optional("MyThread")
myThread priority is :  1.0
myThread is main thread :  false
myThread is executing :  true
myThread is cancelled :  false
myThread is finished :  false
3 seconds later, myThread is executing :  false
3 seconds later, myThread is finished :  true

上面結果中：3秒後子執行緒執行結束。

如果將Timer註釋程式碼開啟後，執行後結果如下:

Main thread is :  <NSThread: 0x600002c6c980>{number = 1, name = MainThread}
Current thread is :  <NSThread: 0x600002c5f000>{number = 7, name = MyThread}
Current thread is main thread :  false
myThread name is :  Optional("MyThread")
myThread priority is :  1.0
myThread is main thread :  false
myThread is executing :  true
myThread is cancelled :  false
myThread is finished :  false
Timer is running
Timer is running
Timer is running
3 seconds later, myThread is executing :  true
3 seconds later, myThread is finished :  false
Timer is running
Timer is running

兩次的執行結果在於3秒後執行緒是否還在執行。

5. NSObject關於Thread的擴充套件方法

一些NSObject關於Thread的擴充套件方法：

	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)

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

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

    open func performSelector(inBackground aSelector: Selector, with arg: Any?)

6. 結束語

Thread是iOS中一個比較輕量級的多執行緒方法，使用起來也比較簡單，另外還有兩種主要的多執行緒方法GCD和Operation，後續文章將會依次介紹這兩個，敬請關注哦！
原文作者：Daniel_Coder
原文地址：https://blog.csdn.net/guoyongming925/article/details/109459607