参考地址

以抢票或秒杀为例

  1. 错误示例1：
  • Service
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    class Service implements Runnable {
        private int remain = 100;

        public AtomicInteger count = new AtomicInteger(0);

        @Override
        public void run() {
            while (remain > 0) {
                System.out.println(Thread.currentThread().getName() + " 剩余：" + this.remain--);
                count.addAndGet(1);
            }
        }
    }
  • 测试方法：
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    public class Main {

        public static int buy() throws InterruptedException {
            Service service = new Service();

            Thread[] threads = new Thread[100];
            for (int i = 0; i < threads.length; i++) {
                threads[i] = new Thread(service);
            }
            for (int i = 0; i < threads.length; i++) {
                threads[i].start();
            }
            Thread.sleep(50);
            return service.count.get();
        }

        public static void main(String[] args) throws InterruptedException {
            int[] array = new int[100];
            for (int i = 0; i < array.length; i++) {
                array[i] = buy();
            }
            long a = Arrays.stream(array).filter(i -> i > 100).count();
            System.out.println("执行次数大于100的个数：" + a);
        }
    }
  • 测试结果：

截图
执行100次中出现了13次下单次数大于100次的情况

  • 原因分析:
    在上述方法中，多个线程共享一个变量，会存在并发争抢资源的问题，可能多买票的现象。