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:selfselector:@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

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// 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:30target:selfselector:@selector(threadTester)userInfo:nilrepeats: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 orientationsreturn (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];}@end