[转]iOS多线程编程之NSThread的使用

你的名字 2021-12-20 02:04 219阅读 0赞

## 1、简介： ##

### 1.1 iOS有三种多线程编程的技术，分别是： ###

1.、[NSThread][]

2、[Cocoa NSOperation][] （[iOS多线程编程之NSOperation和NSOperationQueue的使用][iOS_NSOperation_NSOperationQueue]）

3、[GCD][] 全称：Grand Central Dispatch（ [iOS多线程编程之Grand Central Dispatch(GCD)介绍和使用][iOS_Grand Central Dispatch_GCD]）

这三种编程方式从上到下，抽象度层次是从低到高的，抽象度越高的使用越简单，也是Apple最推荐使用的。

这篇我们主要介绍和使用NSThread，后面会继续2、3 的讲解和使用。

### 1.2 三种方式的有缺点介绍： ###

NSThread:

优点：NSThread 比其他两个轻量级

缺点：需要自己管理线程的生命周期，线程同步。线程同步对数据的加锁会有一定的系统开销

NSThread实现的技术有下面三种：

<table style="color:#000000;font-family:'Lucida Grande', Geneva, Helvetica, Arial, sans-serif;font-size:13px;border-top-color:#9bb3cd;border-left-color:#9bb3cd;border-top-width:1px;border-left-width:1px;border-top-style:solid;border-left-style:solid;"> 
 <tbody> 
 <tr> 
 <th style="color:#ffffff;font-size:13px;font-weight:normal;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Technology </th> 
 <th style="color:#ffffff;font-size:13px;font-weight:normal;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Description </th> 
 </tr> 
 <tr> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Cocoa threads </td> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Cocoa implements threads using the&nbsp;<code style="color:#666666;font-family:Courier, Consolas, monospace;"><a style="color:#003366;text-decoration:none;" href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSThread_Class/Reference/Reference.html#//apple_ref/occ/cl/NSThread" rel="nofollow">NSThread</a></code>&nbsp;class. Cocoa also provides methods on&nbsp;<code style="color:#666666;font-family:Courier, Consolas, monospace;"><a style="color:#003366;text-decoration:none;" href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/cl/NSObject" rel="nofollow">NSObject</a></code>&nbsp;for spawning new threads and executing code on already-running threads. For more information, see&nbsp;<a style="color:#003366;text-decoration:none;" href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW11" rel="nofollow">“Using NSThread”</a>&nbsp;and&nbsp;<a style="color:#003366;text-decoration:none;" href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW13" rel="nofollow">“Using NSObject to Spawn a Thread.”</a> </td> 
 </tr> 
 <tr> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> POSIX threads </td> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> POSIX threads provide a C-based interface for creating threads. If you are not writing a Cocoa application, this is the best choice for creating threads. The POSIX interface is relatively simple to use and offers ample flexibility for configuring your threads. For more information, see&nbsp;<a style="color:#003366;text-decoration:none;" href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW12" rel="nofollow">“Using POSIX Threads”</a> </td> 
 </tr> 
 <tr> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Multiprocessing Services </td> 
 <td style="font-size:13px;vertical-align:middle;border-right-color:#9bb3cd;border-bottom-color:#9bb3cd;border-right-width:1px;border-bottom-width:1px;border-right-style:solid;border-bottom-style:solid;"> Multiprocessing Services is a legacy C-based interface used by applications transitioning from older versions of Mac OS. This technology is available in OS X only and should be avoided for any new development. Instead, you should use the&nbsp;<code style="color:#666666;font-family:Courier, Consolas, monospace;">NSThread</code>&nbsp;class or POSIX threads. If you need more information on this technology, see&nbsp;Multiprocessing Services Programming Guide. </td> 
 </tr> 
 </tbody> 
</table>

一般使用cocoa thread 技术。

**Cocoa operation**

优点：不需要关心线程管理，数据同步的事情，可以把精力放在自己需要执行的操作上。

Cocoa operation 相关的类是 NSOperation ，NSOperationQueue。NSOperation是个抽象类，使用它必须用它的子类，可以实现它或者使用它定义好的两个子类：NSInvocationOperation 和 NSBlockOperation。创建NSOperation子类的对象，把对象添加到NSOperationQueue队列里执行。

**GCD**

Grand Central Dispatch (GCD)是Apple开发的一个多核编程的解决方法。在iOS4.0开始之后才能使用。GCD是一个替代诸如NSThread, NSOperationQueue, NSInvocationOperation等技术的很高效和强大的技术。现在的iOS系统都升级到6了，所以不用担心该技术不能使用。

介绍完这三种多线程编程方式，我们这篇先介绍NSThread的使用。

## 2、NSThread的使用 ##

### 2.1 NSThread 有两种直接创建方式： ###

\- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument

\+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject:(id)anArgument

第一个是实例方法，第二个是类方法

**\[cpp\]** [view plain][] [copy][view plain] [print][view plain] [?][view plain]

1.  1、\[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil\];
2.  2、NSThread\* myThread = \[\[NSThread alloc\] initWithTarget:self
3.  selector:@selector(doSomething:)
4.  object:nil\];
5.  \[myThread start\];

1、[NSThread detachNewThreadSelector:@selector(doSomething:) toTarget:self withObject:nil];
    2、NSThread* myThread = [[NSThread alloc] initWithTarget:self
                                            selector:@selector(doSomething:)
                                            object:nil];
    [myThread start];

### 2.2参数的意义： ###

selector ：线程执行的方法，这个selector只能有一个参数，而且不能有返回值。

target ：selector消息发送的对象

argument:传输给target的唯一参数，也可以是nil

第一种方式会直接创建线程并且开始运行线程，第二种方式是先创建线程对象，然后再运行线程操作，在运行线程操作前可以设置线程的优先级等线程信息

### 2.3 PS:不显式创建线程的方法： ###

用NSObject的类方法 performSelectorInBackground:withObject: 创建一个线程： \[Obj performSelectorInBackground:@selector(doSomething) withObject:nil\];

### 2.4 下载图片的例子： ###

#### 2.4.1 新建singeView app ####

新建项目，并在xib文件上放置一个imageView控件。按住control键拖到viewControll

er.h文件中创建imageView IBOutlet

ViewController.m中实现：

**\[cpp\]** [view plain][] [copy][view plain] [print][view plain] [?][view plain]

1.  //
2.  // ViewController.m
3.  // NSThreadDemo
4.  //
5.  // Created by rongfzh on 12-9-23.
6.  // Copyright (c) 2012年 rongfzh. All rights reserved.
7.  //
8.  
9.  \#import "ViewController.h"
10. \#define kURL @"http://avatar.csdn.net/2/C/D/1\_totogo2010.jpg"
11. @interface ViewController ()
12. 
13. @end
14. 
15. @implementation ViewController
16. 
17. \-(void)downloadImage:(NSString \*) url\{
18. NSData \*data = \[\[NSData alloc\] initWithContentsOfURL:\[NSURL URLWithString:url\]\];
19. UIImage \*image = \[\[UIImage alloc\]initWithData:data\];
20. if(image == nil)\{
21. 
22. \}else\{
23. \[self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES\];
24. \}
25. \}
26. 
27. \-(void)updateUI:(UIImage\*) image\{
28. self.imageView.image = image;
29. \}
30. 
31. 
32. \- (void)viewDidLoad
33. \{
34. \[super viewDidLoad\];
35. 
36. // \[NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL\];
37. NSThread \*thread = \[\[NSThread alloc\]initWithTarget:self selector:@selector(downloadImage:) object:kURL\];
38. \[thread start\];
39. \}
40. 
41. \- (void)didReceiveMemoryWarning
42. \{
43. \[super didReceiveMemoryWarning\];
44. // Dispose of any resources that can be recreated.
45. \}
46. 
47. @end

//
    //  ViewController.m
    //  NSThreadDemo
    //
    //  Created by rongfzh on 12-9-23.
    //  Copyright (c) 2012年 rongfzh. All rights reserved.
    //
    
    #import "ViewController.h"
    #define kURL @"http://avatar.csdn.net/2/C/D/1_totogo2010.jpg"
    @interface ViewController ()
    
    @end
    
    @implementation ViewController
    
    -(void)downloadImage:(NSString *) url{
        NSData *data = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:url]];
        UIImage *image = [[UIImage alloc]initWithData:data];
        if(image == nil){
            
        }else{
            [self performSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES];
        }
    }
    
    -(void)updateUI:(UIImage*) image{
        self.imageView.image = image;
    }
    
    
    - (void)viewDidLoad
    {
        [super viewDidLoad];
        
    //    [NSThread detachNewThreadSelector:@selector(downloadImage:) toTarget:self withObject:kURL];
        NSThread *thread = [[NSThread alloc]initWithTarget:self selector:@selector(downloadImage:) object:kURL];
        [thread start];
    }
    
    - (void)didReceiveMemoryWarning
    {
        [super didReceiveMemoryWarning];
        // Dispose of any resources that can be recreated.
    }
    
    @end

#### 2.4.2线程间通讯 ####

线程下载完图片后怎么通知主线程更新界面呢？

\[selfperformSelectorOnMainThread:@selector(updateUI:) withObject:image waitUntilDone:YES\];

performSelectorOnMainThread是NSObject的方法，除了可以更新主线程的数据外，还可以更新其他线程的比如：

用：performSelector:onThread:withObject:waitUntilDone:

运行下载图片：

![1348412756_8445.png][]

图片下载下来了。

### 2.3 线程同步 ###

我们演示一个经典的卖票的例子来讲NSThread的线程同步：

**\[cpp\]** [view plain][] [copy][view plain] [print][view plain] [?][view plain]

1. \#import <UIKit/UIKit.h>
2. 
3. @class ViewController;
4. 
5. @interface AppDelegate : UIResponder <UIApplicationDelegate>
6. \{
7. int tickets;
8. int count;
9. NSThread\* ticketsThreadone;
10. NSThread\* ticketsThreadtwo;
11. NSCondition\* ticketsCondition;
12. NSLock \*theLock;
13. \}
14. @property (strong, nonatomic) UIWindow \*window;
15. 
16. @property (strong, nonatomic) ViewController \*viewController;
17. 
18. @end

#import <UIKit/UIKit.h>
 
 @class ViewController;
 
 @interface AppDelegate : UIResponder <UIApplicationDelegate>
 {
 int tickets;
 int count;
 NSThread* ticketsThreadone;
 NSThread* ticketsThreadtwo;
 NSCondition* ticketsCondition;
 NSLock *theLock;
 }
 @property (strong, nonatomic) UIWindow *window;
 
 @property (strong, nonatomic) ViewController *viewController;
 
 @end

**\[cpp\]** [view plain][] [copy][view plain] [print][view plain] [?][view plain]

1.  \- (BOOL)application:(UIApplication \*)application didFinishLaunchingWithOptions:(NSDictionary \*)launchOptions
2.  \{
3.  
4.  tickets = 100;
5.  count = 0;
6.  theLock = \[\[NSLock alloc\] init\];
7.  // 锁对象
8.  ticketsCondition = \[\[NSCondition alloc\] init\];
9.  ticketsThreadone = \[\[NSThread alloc\] initWithTarget:self selector:@selector(run) object:nil\];
10. \[ticketsThreadone setName:@"Thread-1"\];
11. \[ticketsThreadone start\];
12. 
13. 
14. ticketsThreadtwo = \[\[NSThread alloc\] initWithTarget:self selector:@selector(run) object:nil\];
15. \[ticketsThreadtwo setName:@"Thread-2"\];
16. \[ticketsThreadtwo start\];
17. 
18. self.window = \[\[UIWindow alloc\] initWithFrame:\[\[UIScreen mainScreen\] bounds\]\];
19. // Override point for customization after application launch.
20. self.viewController = \[\[ViewController alloc\] initWithNibName:@"ViewController" bundle:nil\];
21. self.window.rootViewController = self.viewController;
22. \[self.window makeKeyAndVisible\];
23. return YES;
24. \}
25. 
26. \- (void)run\{
27. while (TRUE) \{
28. // 上锁
29. // \[ticketsCondition lock\];
30. \[theLock lock\];
31. if(tickets >= 0)\{
32. \[NSThread sleepForTimeInterval:0.09\];
33. count = 100 - tickets;
34. NSLog(@"当前票数是:%d,售出:%d,线程名:%@",tickets,count,\[\[NSThread currentThread\] name\]);
35. tickets--;
36. \}else\{
37. break;
38. \}
39. \[theLock unlock\];
40. // \[ticketsCondition unlock\];
41. \}
42. \}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
        
        tickets = 100;
        count = 0;
        theLock = [[NSLock alloc] init];
        // 锁对象
        ticketsCondition = [[NSCondition alloc] init];
        ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
        [ticketsThreadone setName:@"Thread-1"];
        [ticketsThreadone start];
        
        
        ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
        [ticketsThreadtwo setName:@"Thread-2"];
        [ticketsThreadtwo start];
        
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        // Override point for customization after application launch.
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.window.rootViewController = self.viewController;
        [self.window makeKeyAndVisible];
        return YES;
    }
    
    - (void)run{
        while (TRUE) {
            // 上锁
    //        [ticketsCondition lock];
            [theLock lock];
            if(tickets >= 0){
                [NSThread sleepForTimeInterval:0.09];
                count = 100 - tickets;
                NSLog(@"当前票数是:%d,售出:%d,线程名:%@",tickets,count,[[NSThread currentThread] name]);
                tickets--;
            }else{
                break;
            }
            [theLock unlock];
    //        [ticketsCondition unlock];
        }
    }

如果没有线程同步的lock，卖票数可能是-1.加上lock之后线程同步保证了数据的正确性。 上面例子我使用了两种锁，一种NSCondition ，一种是：NSLock。 NSCondition我已经注释了。

#### 线程的顺序执行 ####

他们都可以通过

\[ticketsConditionsignal\]; 发送信号的方式，在一个线程唤醒另外一个线程的等待。

比如：

**\[cpp\]** [view plain][] [copy][view plain] [print][view plain] [?][view plain]

1.  \#import "AppDelegate.h"
2.  
3.  \#import "ViewController.h"
4.  
5.  @implementation AppDelegate
6.  
7.  \- (BOOL)application:(UIApplication \*)application didFinishLaunchingWithOptions:(NSDictionary \*)launchOptions
8.  \{
9.  
10. tickets = 100;
11. count = 0;
12. theLock = \[\[NSLock alloc\] init\];
13. // 锁对象
14. ticketsCondition = \[\[NSCondition alloc\] init\];
15. ticketsThreadone = \[\[NSThread alloc\] initWithTarget:self selector:@selector(run) object:nil\];
16. \[ticketsThreadone setName:@"Thread-1"\];
17. \[ticketsThreadone start\];
18. 
19. ticketsThreadtwo = \[\[NSThread alloc\] initWithTarget:self selector:@selector(run) object:nil\];
20. \[ticketsThreadtwo setName:@"Thread-2"\];
21. \[ticketsThreadtwo start\];
22. 
23. NSThread \*ticketsThreadthree = \[\[NSThread alloc\] initWithTarget:self selector:@selector(run3) object:nil\];
24. \[ticketsThreadthree setName:@"Thread-3"\];
25. \[ticketsThreadthree start\];
26. self.window = \[\[UIWindow alloc\] initWithFrame:\[\[UIScreen mainScreen\] bounds\]\];
27. // Override point for customization after application launch.
28. self.viewController = \[\[ViewController alloc\] initWithNibName:@"ViewController" bundle:nil\];
29. self.window.rootViewController = self.viewController;
30. \[self.window makeKeyAndVisible\];
31. return YES;
32. \}
33. 
34. \-(void)run3\{
35. while (YES) \{
36. \[ticketsCondition lock\];
37. \[NSThread sleepForTimeInterval:3\];
38. \[ticketsCondition signal\];
39. \[ticketsCondition unlock\];
40. \}
41. \}
42. 
43. \- (void)run\{
44. while (TRUE) \{
45. // 上锁
46. \[ticketsCondition lock\];
47. \[ticketsCondition wait\];
48. \[theLock lock\];
49. if(tickets >= 0)\{
50. \[NSThread sleepForTimeInterval:0.09\];
51. count = 100 - tickets;
52. NSLog(@"当前票数是:%d,售出:%d,线程名:%@",tickets,count,\[\[NSThread currentThread\] name\]);
53. tickets--;
54. \}else\{
55. break;
56. \}
57. \[theLock unlock\];
58. \[ticketsCondition unlock\];
59. \}
60. \}

#import "AppDelegate.h"
    
    #import "ViewController.h"
    
    @implementation AppDelegate
    
    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    {
        
        tickets = 100;
        count = 0;
        theLock = [[NSLock alloc] init];
        // 锁对象
        ticketsCondition = [[NSCondition alloc] init];
        ticketsThreadone = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
        [ticketsThreadone setName:@"Thread-1"];
        [ticketsThreadone start];
        
        ticketsThreadtwo = [[NSThread alloc] initWithTarget:self selector:@selector(run) object:nil];
        [ticketsThreadtwo setName:@"Thread-2"];
        [ticketsThreadtwo start];
        
        NSThread *ticketsThreadthree = [[NSThread alloc] initWithTarget:self selector:@selector(run3) object:nil];
        [ticketsThreadthree setName:@"Thread-3"];
        [ticketsThreadthree start];    
        self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
        // Override point for customization after application launch.
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
        self.window.rootViewController = self.viewController;
        [self.window makeKeyAndVisible];
        return YES;
    }
    
    -(void)run3{
        while (YES) {
            [ticketsCondition lock];
            [NSThread sleepForTimeInterval:3];
            [ticketsCondition signal];
            [ticketsCondition unlock];
        }
    }
    
    - (void)run{
        while (TRUE) {
            // 上锁
            [ticketsCondition lock];
            [ticketsCondition wait];
            [theLock lock];
            if(tickets >= 0){
                [NSThread sleepForTimeInterval:0.09];
                count = 100 - tickets;
                NSLog(@"当前票数是:%d,售出:%d,线程名:%@",tickets,count,[[NSThread currentThread] name]);
                tickets--;
            }else{
                break;
            }
            [theLock unlock];
            [ticketsCondition unlock];
        }
    }

wait是等待，我加了一个 线程3 去唤醒其他两个线程锁中的wait

#### 其他同步 ####

我们可以使用指令 @synchronized 来简化 NSLock的使用，这样我们就不必显示编写创建NSLock,加锁并解锁相关代码。 - (void)doSomeThing:(id)anObj \{ @synchronized(anObj) \{ // Everything between the braces is protected by the @synchronized directive. \} \} 还有其他的一些锁对象，比如：循环锁NSRecursiveLock，条件锁NSConditionLock，分布式锁NSDistributedLock等等,可以自己看官方文档学习

NSThread下载图片的例子代码：[http://download.csdn.net/detail/totogo2010/4591149][http_download.csdn.net_detail_totogo2010_4591149]

著作权声明：本文由[http://blog.csdn.net/totogo2010/][http_blog.csdn.net_totogo2010]原创，欢迎转载分享。请尊重作者劳动，转载时保留该声明和作者博客链接，谢谢!

转载于:https://www.cnblogs.com/haibosoft/p/3723408.html

[NSThread]: https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSThread_Class/Reference/Reference.html
[Cocoa NSOperation]: https://developer.apple.com/documentation/Cocoa/Reference/NSOperation_class/Reference/Reference.html
[iOS_NSOperation_NSOperationQueue]: http://blog.csdn.net/totogo2010/article/details/8013316
[GCD]: http://developer.apple.com/library/ios/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html%23//apple_ref/doc/uid/TP40008079
[iOS_Grand Central Dispatch_GCD]: http://blog.csdn.net/totogo2010/article/details/8016129
[view plain]: http://blog.csdn.net/totogo2010/article/details/8010231
[1348412756_8445.png]: https://img-my.csdn.net/uploads/201209/23/1348412756_8445.png
[http_download.csdn.net_detail_totogo2010_4591149]: http://download.csdn.net/detail/totogo2010/4591149
[http_blog.csdn.net_totogo2010]: http://blog.csdn.net/totogo2010/