线程3--线程安全

线程安全指的是当多个线程可能会访问同一块资源

比如多个线程访问同一个对象、同一个变量、同一个文件

当多个线程访问同一块资源时，很容易引发数据错乱和数据安全问题

 

- (void)viewDidLoad {
    //默认有20张票
    self.leftTicketsCount=20;
    //开启多个线程，模拟售票员售票
    
    self.thread1=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
    
    self.thread1.name=@"售票员A";
    
    self.thread2=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
    
    self.thread2.name=@"售票员B";
    
    self.thread3=[[NSThread alloc]initWithTarget:self selector:@selector(sellTickets) object:nil];
    
    self.thread3.name=@"售票员C";
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}
-(void)sellTickets
{
    while (1) {
        @synchronized(self){//只能加一把锁,下面为同步代码块；
            //1.先检查票数
            int count=self.leftTicketsCount;
            if (count>0) {
                //暂停一段时间
                [NSThread sleepForTimeInterval:0.002];
                //2.票数-1
                self.leftTicketsCount= count-1;
                //获取当前线程
                NSThread *current=[NSThread currentThread];
                NSLog(@"%@--卖了一张票，还剩余%d张票",current,self.leftTicketsCount);
            }else
            {
                //退出线程
                [NSThread exit];
            }
        }
    }
}


-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    
    //开启线程
    [self.thread1 start];
    [self.thread2 start];
    [self.thread3 start];
}