数据竞争

多线程数据竞争demo~~~

数据竞争代码举例以及用互斥锁解决

// ViewController.m
//售票员卖票demo

@interface ViewController() 
   
@property(nonatomic, strong) NSThread *threadA;
@property(nonatomic, strong) NSThread *threadB;
@property(nonatomic, strong) NSThread *threadC;
    
@end
    
@implementation ViewController

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
    
    self.ticketCount = 100;
    //开启三个售票员线程
    self.threadA = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
    self.threadB = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
    self.threadC = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
    
    //线程属性设置
    self.threadA.name = @"售票员A";
    self.threadB.name = @"售票员B";
    self.threadC.name = @"售票员C";
    
    //启动线程
    [self.threadA start];
    [self.threadB start];
    [self.threadC start];
    
}

- (void)saleTicket {
    while(1) {
        @synchronized (self) {
            //对于每一次卖票的模块上锁，保证同一时间只有一位售票员在卖票
            if(self.ticketCount > 0) {
                //卖出去一张票
                for(int i = 1; i <= 100000; i++); //增加程序执行时间，方便观察结果
                NSLog(@"%@卖出去一张，还剩下%zd张", [NSThread currentThread].name, self.ticketCount - 1);
                self.ticketCount--;
            } else {
                NSLog(@"票已售罄");
                break;
            }
        }
    }
}

@end