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。

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。

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：

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