数据竞争

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//售票员卖票demo
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@interface ViewController()
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@property(nonatomic, strong) NSThread *threadA;
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@property(nonatomic, strong) NSThread *threadB;
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@property(nonatomic, strong) NSThread *threadC;
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@end
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@implementation ViewController
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- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event {
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    self.ticketCount = 100;
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    //开启三个售票员线程
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    self.threadA = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
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    self.threadB = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
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    self.threadC = [[NSThread alloc] initWithTarget:self selector:@selector(saleTicket) object:nil];
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    //线程属性设置
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    self.threadA.name = @"售票员A";
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    self.threadB.name = @"售票员B";
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    self.threadC.name = @"售票员C";
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    //启动线程
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    [self.threadA start];
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    [self.threadB start];
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    [self.threadC start];
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}
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- (void)saleTicket {
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    while(1) {
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        @synchronized (self) {
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            //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
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            if(self.ticketCount > 0) {
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                //卖出去一张票
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                for(int i = 1; i <= 100000; i++); //增加程序执行时间，方便观察结果
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                NSLog(@"%@卖出去一张，还剩下%zd张", [NSThread currentThread].name, self.ticketCount - 1);
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                self.ticketCount--;
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            } else {
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                NSLog(@"票已售罄");
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                break;
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            }
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        }
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    }
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}
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@end