iOS多线程编程之NSThread的使用

秒速五厘米 2022-08-05 15:03 186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:rgb(0,0,0); line-height:25.98958396911621px; border-top-width:1px; border-top-style:solid; border-top-color:rgb(155,179,205); border-left-width:1px; border-left-style:solid; border-left-color:rgb(155,179,205); margin-bottom:4em; font-family:'Lucida Grande',Geneva,Helvetica,Arial,sans-serif; font-size:13px"> 
 <tbody> 
 <tr> 
 <th style="font-weight:normal; background-color:rgb(147,165,187); padding:0.3em 0.667em; font-size:13px; color:rgb(255,255,255); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> Technology </th> 
 <th style="font-weight:normal; background-color:rgb(147,165,187); padding:0.3em 0.667em; font-size:13px; color:rgb(255,255,255); border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> Description </th> 
 </tr> 
 <tr> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> Cocoa threads </td> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> Cocoa implements threads using the&nbsp;<code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)"><a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSThread_Class/Reference/Reference.html#//apple_ref/occ/cl/NSThread" style="color:rgb(0,51,102); text-decoration:none" rel="nofollow">NSThread</a></code>&nbsp;class. Cocoa also provides methods on&nbsp;<code style="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)"><a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/cl/NSObject" style="color:rgb(0,51,102); text-decoration:none" rel="nofollow">NSObject</a></code>&nbsp;for spawning new threads and executing code on already-running threads. For more information, see&nbsp;<a href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW11" style="color:rgb(0,51,102); text-decoration:none" rel="nofollow">“Using NSThread”</a>&nbsp;and&nbsp;<a href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW13" style="color:rgb(0,51,102); text-decoration:none" rel="nofollow">“Using NSObject to Spawn a Thread.”</a> </td> 
 </tr> 
 <tr> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> POSIX threads </td> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> 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 href="https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/CreatingThreads.html#//apple_ref/doc/uid/10000057i-CH15-SW12" style="color:rgb(0,51,102); text-decoration:none" rel="nofollow">“Using POSIX Threads”</a> </td> 
 </tr> 
 <tr> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> Multiprocessing Services </td> 
 <td style="padding:0.667em; font-size:13px; vertical-align:middle; border-bottom-width:1px; border-bottom-style:solid; border-bottom-color:rgb(155,179,205); border-right-width:1px; border-right-style:solid; border-right-color:rgb(155,179,205)"> 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="font-family:Courier,Consolas,monospace; color:rgb(102,102,102)">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]

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.  \[myThread start\];

### 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]

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

#### 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]

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

**\[cpp\]** [view plain][] [copy][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. \}

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]

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. \}

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!

[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#//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/