object-c 多线程 加锁

object-c的多线程如java的多线程一样方便可靠。

一、线程创建与启动
线程创建主要有二种方式：
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- (id)init; // designated initializer
- (id)initWithTarget:(id)target selector:(SEL)selector object:(id)argument;

当然，还有一种比较特殊，就是使用所谓的convenient method，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。这个方法的接口是：
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+ (void)detachNewThreadSelector:(SEL)aSelector toTarget:(id)aTarget withObject：(id)anArgument

前两种方法创建后，需要手机启动，启动的方法是：
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- (void)start;

二、线程的同步与锁
要说明线程的同步与锁，最好的例子可能就是多个窗口同时售票的售票系统了。我们知道在java中，使用synchronized来同步，而iphone虽 然没有提供类似java下的synchronized关键字，但提供了NSCondition对象接口。查看NSCondition的接口说明可以看 出，NSCondition是iphone下的锁对象，所以我们可以使用NSCondition实现iphone中的线程安全。这是来源于网上的一个例 子：

SellTicketsAppDelegate.h 文件
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// SellTicketsAppDelegate.h
import
@interface SellTicketsAppDelegate : NSObject {
int tickets;
int count;
NSThread* ticketsThreadone;
NSThread* ticketsThreadtwo;
NSCondition* ticketsCondition;
UIWindow *window;
}
@property (nonatomic, retain) IBOutlet UIWindow *window;
@end

SellTicketsAppDelegate.m 文件
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// SellTicketsAppDelegate.m
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

三、线程的交互
线程在运行过程中，可能需要与其它线程进行通信，如在主线程中修改界面等等，可以使用如下接口：
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- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait

由于在本过程中，可能需要释放一些资源，则需要使用NSAutoreleasePool来进行管理,如：
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- (void)startTheBackgroundJob {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
// to do something in your thread job
…
[self performSelectorOnMainThread:@selector(makeMyProgressBarMoving) withObject:nil waitUntilDone:NO];
[pool release];
}

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