Swift

1，Swift继续使用Object-C原有的一套线程，包括三种多线程编程技术：

（1）NSThread

（2）Cocoa NSOperation（NSOperation和NSOperationQueue）

（3）Grand Central Dispath（GCD）

2，本文着重介绍NSThread

NSTread在三种多线程技术中是最轻量级的，但需要自己管理线程的生命周期和线程同步。线程同步对数据的加锁会有一定的系统开销。

3，NSThread的两种创建方式

（1）直接创建线程并且自动运行线程

（2）先创建一个线程对象，然后手动运行线程，在运行线程操作之前可以设置线程的优先级等线程信息。

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import UIKit   class ViewController: UIViewController {       override func viewDidLoad() {         super.viewDidLoad()                   //方式1：使用类方法         NSThread.detachNewThreadSelector("downloadImage", toTarget: self, withObject: nil)                   //方式2：实例方法-便利构造器         var myThread:NSThread = NSThread(target: self, selector: "downloadImage", object: nil)         myThread.start()     }           //定义一个下载图片的方法，线程调用     func downloadImage(){         var imageUrl = "http://hangge.com/blog/images/logo.png"         var data = NSData(contentsOfURL: NSURL(string: imageUrl)!, options: nil, error: nil)         println(data?.length)     }           override func didReceiveMemoryWarning() {         super.didReceiveMemoryWarning()         // Dispose of any resources that can be recreated.     } }

4，线程同步

线程同步方法通过锁来实现，每个线程都只用一个锁，这个锁与一个特定的线程关联。下面演示两个线程之间的同步。

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import UIKit   class ViewController: UIViewController {           //定义两个线程     var thread1:NSThread?     var thread2:NSThread?           //定义两个线程条件，用于锁住线程     let condition1 = NSCondition()     let condition2 = NSCondition()       override func viewDidLoad() {         super.viewDidLoad()                   thread2 = NSThread(target: self, selector: "method2:", object: nil)         thread1 = NSThread(target: self, selector: "method1:", object: nil)         thread1?.start()     }           //定义两方法，用于两个线程调用     func method1(sender:AnyObject){         for var i=0; i<10; i++ {             print("NSThread 1 running (i)")             sleep(1)                           if i == 2 {                 thread2?.start() //启动线程2                                   //本线程（thread1）锁定                 condition1.lock()                 condition1.wait()                 condition1.unlock()             }         }                       print("NSThread 1 over")                   //线程2激活         condition2.signal()     }           //方法2     func method2(sender:AnyObject){         for var i=0; i<10; i++ {             print("NSThread 2 running (i)")             sleep(1)                           if i == 2 {                 //线程1激活                 condition1.signal()                                   //本线程（thread2）锁定                 condition2.lock()                 condition2.wait()                 condition2.unlock()             }         }                    print("NSThread 2 over")     }           override func didReceiveMemoryWarning() {         super.didReceiveMemoryWarning()         // Dispose of any resources that can be recreated.     } }

输出结果：

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NSThread 1 running 0 NSThread 1 running 1 NSThread 1 running 2 NSThread 2 running 0 NSThread 2 running 1 NSThread 2 running 2 NSThread 1 running 3 NSThread 1 running 4 NSThread 1 running 5 NSThread 1 running 6 NSThread 1 running 7 NSThread 1 running 8 NSThread 1 running 9 NSThread 1 over NSThread 2 running 3 NSThread 2 running 4 NSThread 2 running 5 NSThread 2 running 6 NSThread 2 running 7 NSThread 2 running 8 NSThread 2 running 9 NSThread 2 over