NSThread 售票员售票问题

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

self.tickets = 20;

NSThread *threadA = [[NSThread alloc] initWithTarget:self selector:@selector(saleTickets) object:nil];
threadA.name = @"售票员 A";
[threadA start];
NSThread *threadB = [[NSThread alloc] initWithTarget:self selector:@selector(saleTickets) object:nil];
threadB.name = @"售票员 B";
[threadB start];
}

- (void)saleTickets
{
while (YES)
{
// 模拟休眠
[NSThread sleepForTimeInterval:1.0f];
//枷锁 防止资源抢夺错误
@synchronized(self) {
if (self.tickets > 0)
{
self.tickets--;
NSLog(@"剩余票数 %@ %d", [NSThread currentThread], self.tickets);

}
else
{
break;
}
}
}
}