iPhone开发之多线程之NSInvocationOperation

多线程编程是防止主线程堵塞，增加运行效率等等的最佳方法。而原始的多线程方法存在很多的毛病，包括线程锁死等。在Cocoa中，Apple提供了NSOperation这个类，提供了一个优秀的多线程编程方法。

本次介绍NSOperation的子集，简易方法的NSInvocationOperation： 
@implementation MyCustomClass 
- (void)launchTaskWithData:(id)data 
{ 
//创建一个NSInvocationOperation对象，并初始化到方法 
//在这里，selector参数后的值是你想在另外一个线程中运行的方法（函数，Method） 
//在这里，object后的值是想传递给前面方法的数据 
NSInvocationOperation* theOp = [[NSInvocationOperation alloc] initWithTarget:self 
selector:@selector(myTaskMethod:) object:data];

// 下面将我们建立的操作“Operation”加入到本地程序的共享队列中（加入后方法就会立刻被执行） 
// 更多的时候是由我们自己建立“操作”队列 
[[MyAppDelegate sharedOperationQueue] addOperation:theOp]; 
}

// 这个是真正运行在另外一个线程的“方法” 
- (void)myTaskMethod:(id)data 
{ 
// Perform the task. 
}

@end一个NSOperationQueue 操作队列，就相当于一个线程管理器，而非一个线程。因为你可以设置这个线程管理器内可以并行运行的的线程数量等等。下面是建立并初始化一个操作队列：

@interface MyViewController : UIViewController {

NSOperationQueue *operationQueue; 
//在头文件中声明该队列 
} 
@end

@implementation MyViewController

- (id)init 
{ 
self = [super init]; 
if (self) { 
operationQueue = [[NSOperationQueue alloc] init]; //初始化操作队列 
[operationQueue setMaxConcurrentOperationCount:1]; 
//在这里限定了该队列只同时运行一个线程 
//这个队列已经可以使用了 
} 
return self; 
}

- (void)dealloc 
{ 
[operationQueue release]; 
//正如Alan经常说的，我们是程序的好公民，需要释放内存！ 
[super dealloc]; 
}

@end简单介绍之后，其实可以发现这种方法是非常简单的。很多的时候我们使用多线程仅仅是为了防止主线程堵塞，而NSInvocationOperation就是最简单的多线程编程，在iPhone编程中是经常被用到的。

 

/////////////////////////////////////////////////////////////////////////////////////////////////// 
1 在主线程里加入一个loading画面…… 
2 { 
3 [window addSubview:view_loading]; 
4 [NSThread detachNewThreadSelector:@selector(init_backup:) toTarget:self withObject:nil]; 
5 } 
可以通过performSelectorOnMainThread更新UI元素，比如设置进度条等等。最后消除loading画面，载入主View。 
7 - (void)init_backup:(id)sender 
8 { 
9 NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; 
10 
11 // ... 
12 int i = status; 
13 [self performSelectorOnMainThread:@selector(show_loading:) withObject:[NSNumber numberWithInt:i] waitUntil Done:NO]; 
14 
15 [view_loading removeFromSuperview]; 
16 [window addSubview:tabcontroller_main.view]; 
17 [pool release]; 
18 }

///////////////////////////////////////////////////////

利用iphone的多线程实现和线程同步

从接口的定义中可以知道，NSThread和大多数iphone的接口对象一样，有两种方式可以初始化：

一种使用initWithTarget:(id)target selector:(SEL)selector object:(id)argument，但需要负责在对象的retain count为0时调用对象的release方法清理对象。

另一种则使用所谓的convenient method,这个方便接口就是detachNewThreadSelector，这个方法可以直接生成一个线程并启动它，而且无需为线程的清理负责。

#import <UIKit/UIKit.h> 
@interface SellTicketsAppDelegate : NSObject <UIApplicationDelegate> { 
int tickets; 
int count; 
NSThread* ticketsThreadone; 
NSThread* ticketsThreadtwo; 
NSCondition* ticketsCondition; 
UIWindow *window; 
}

@property (nonatomic, retain) IBOutlet UIWindow *window; 
@end

然后在实现中添加如下代码： 
// SellTicketsAppDelegate.m 
// SellTickets 
// 
// 
#import "SellTicketsAppDelegate.h" 
@implementation SellTicketsAppDelegate 
@synthesize window; 
- (void)applicationDidFinishLaunching:(UIApplication *)application { 
tickets = 100; 
count = 0; 
// 锁对象 
ticketCondition = [[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 detachNewThreadSelector:@selector(run) toTarget:self withObject:nil]; 
// Override point for customization after application launch 
[window makeKeyAndVisible]; 
} 
- (void)run{ 
while (TRUE) { 
// 上锁 
[ticketsCondition lock]; 
if(tickets > 0) 
{ 
[NSThread sleepForTimeInterval:0.5]; 
count = 100 - tickets; 
NSLog(@"当前票数是:%d,售出:%d,线程名:%@",tickets,count,[[NSThread currentThread] name]); 
tickets--; 
}else 
{ 
break; 
} 
[ticketsCondition unlock]; 
} 
} 
- (void)dealloc { 
[ticketsThreadone release]; 
[ticketsThreadtwo release]; 
[ticketsCondition release]; 
[window release]; 
[super dealloc]; 
} 
@end

------------------------------------------------------------------------------------- 
// 定义 
#import <UIKit/UIKit.h>

@interface ThreadSyncSampleViewController : UIViewController { 
int _threadCount; 
NSCondition *_myCondition; 
}

@end

//实现文件如下:

#import "ThreadSyncSampleViewController.h"

@implementation ThreadSyncSampleViewController

/* 
// The designated initializer. Override to perform setup that is required before the view is loaded. 
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil { 
if (self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil]) { 
// Custom initialization 
} 
return self; 
} 
*/

/* 
// Implement loadView to create a view hierarchy programmatically, without using a nib. 
- (void)loadView { 
} 
*/

// Implement viewDidLoad to do additional setup after loading the view, typically from a nib. 
- (void)viewDidLoad { 
[super viewDidLoad]; 
// 
//_myCondition = nil; 
// 
_myCondition = [[NSCondition alloc] init]; 
// 
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:30 
target:self 
selector:@selector(threadTester) 
userInfo:nil 
repeats:YES]; 
[timer fire];

}

- (void)threadTester{ 
[_myCondition lock];

_threadCount = -2; 
//如果有n个要等待的thread，这里置成 -n 
[_myCondition unlock]; 
// 
NSLog(@""); 
NSLog(@"------------------------------------------------------------------------------"); 
[NSThread detachNewThreadSelector:@selector(threadOne) toTarget:self withObject:nil]; 
[NSThread detachNewThreadSelector:@selector(threadTwo) toTarget:self withObject:nil]; 
[NSThread detachNewThreadSelector:@selector(threadThree) toTarget:self withObject:nil]; 
return; 
}

- (void)threadOne{ 
NSLog(@"@@@ In thread 111111 start."); 
[_myCondition lock];

int n = rand()%5 + 1; 
NSLog(@"@@@ Thread 111111 Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount); 
sleep(n); 
//[NSThread sleepForTimeInterval:n]; 
_threadCount ++ ; 
NSLog(@"@@@ Thread 111111 has sleep %d seconds ,now _threadCount is : %d",n,_threadCount); 
[_myCondition signal]; 
NSLog(@"@@@ Thread 1111111 has signaled ,now _threadCount is : %d",_threadCount); 
[_myCondition unlock]; 
NSLog(@"@@@ In thread one complete."); 
[NSThread exit]; 
return; 
}

- (void)threadTwo{ 
NSLog(@"### In thread 2222222 start."); 
[_myCondition lock];

int n = rand()%5 + 1; 
NSLog(@"### Thread 2222222 Will sleep %d seconds ,now _threadCount is : %d",n,_threadCount); 
sleep(n); 
// [NSThread sleepForTimeInterval:n]; 
_threadCount ++ ; 
NSLog(@"### Thread 2222222 has sleep %d seconds ,now _threadCount is : %d",n,_threadCount); 
[_myCondition signal]; 
NSLog(@"### Thread 2222222 has signaled ,now _threadCount is : %d",_threadCount); 
[_myCondition unlock]; 
//_threadCount ++ ; 
NSLog(@"### In thread 2222222 complete."); 
[NSThread exit]; 
return; 
}

- (void)threadThree{ 
NSLog(@"<<< In thread 333333 start."); 
[_myCondition lock]; 
while (_threadCount < 0) { 
[_myCondition wait]; 
} 
NSLog(@"<<< In thread 333333 ,_threadCount now is %d ,will start work.",_threadCount); 
[_myCondition unlock]; 
NSLog(@"<<< In thread 333333 complete."); 
[NSThread exit]; 
return; 
}

/* 
// Override to allow orientations other than the default portrait orientation. 
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { 
// Return YES for supported orientations 
return (interfaceOrientation == UIInterfaceOrientationPortrait); 
} 
*/

- (void)didReceiveMemoryWarning { 
// Releases the view if it doesn't have a superview. 
[super didReceiveMemoryWarning];

// Release any cached data, images, etc that aren't in use. 
}

- (void)viewDidUnload { 
// Release any retained subviews of the main view. 
// e.g. self.myOutlet = nil; 
}

- (void)dealloc { 
[_myCondition release]; 
[super dealloc]; 
}