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import “ViewController.h”

@interface ViewController ()

{

UILabel *showTicket;

int curtTicketNum; //当前票数

int saleTicketNum; // 销售票数

NSString *windowName; //窗口名字

NSCondition *condition;//线程锁

}

@end

@implementation ViewController

(void)viewDidLoad {

[super viewDidLoad];

curtTicketNum = 100;

self.view.backgroundColor = [UIColor brownColor];

// 卖票系统 分三个窗口同时销售

UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];
button.frame = CGRectMake(100, 100, 100, 50);
[button setTitle:@"开始卖票" forState:UIControlStateNormal];
[button addTarget:self action:@selector(startSale) forControlEvents:UIControlEventTouchUpInside];
[self.view addSubview:button];

showTicket = [[UILabel alloc]init];
showTicket.frame = CGRectMake(200, 100, 100, 500);
showTicket.text = @"余票:100张";
showTicket.textAlignment = NSTextAlignmentCenter;
showTicket.numberOfLines = 5;
showTicket.textColor = [UIColor redColor];
[self.view addSubview:showTicket];

}

//三个窗口同时卖票

-(void)startSale

{

//初始化三个线程 每一个线程都是一个售票窗口

NSThread *window1 = [[NSThread alloc]initWithTarget:self selector:@selector(saleTicket) object:nil];

window1.name = @”售票窗口1”;

[window1 start];

NSThread *window2 = [[NSThread alloc]initWithTarget:self selector:@selector(saleTicket) object:nil];
window2.name = @"售票窗口2";
[window2 start];

NSThread *window3 = [[NSThread alloc]initWithTarget:self selector:@selector(saleTicket) object:nil];
window3.name = @"售票窗口3";
[window3 start];

// 线程锁 NSCondition 是一个线程锁（条件锁）

condition = [[NSCondition alloc]init];

}

-(void)saleTicket

{

// 没有使用线程锁 三个线程（窗口）会同时访问这个方法（卖票的方法） 所以 当剩余票数是0的时候 有可能其他两个线程 不知道剩余票数是0 还会同时访问，此事剩余票数会出现负数的情况

// 解决这个问题 可以使用线程锁

// 只允许一个线程访问完毕之后，另外一个线程再去访问

// 使用线程锁 值允许一个线程去访问

while (curtTicketNum>0) {
[condition lock];//锁住
[NSThread sleepForTimeInterval:0.1];

// 当前票数(剩余)

curtTicketNum -=1;

// 卖的票数

saleTicketNum = 100-curtTicketNum;

windowName = [NSThread currentThread].name;

if (curtTicketNum>0) {

[condition unlock]; //当一个窗口卖完票后在解锁

}

[self performSelectorOnMainThread:@selector(upDataUI) withObject:nil waitUntilDone:YES];

}
curtTicketNum = 100;

}

//更新界面

-(void)upDataUI

{

showTicket.text = [NSString stringWithFormat:@”已经销售%d 还剩%d 当前窗口是%@”,saleTicketNum,curtTicketNum,windowName];

}

- (void)didReceiveMemoryWarning {

[super didReceiveMemoryWarning];

// Dispose of any resources that can be recreated.

}

@end