高并发-原子性-AtomicInteger

线程不安全：

//请求总次数
private static int totalCount = 10000;
//最大并发数
private static int totalCurrency = 100;
//计数初始值
private static int count = 0;

public static void main(String[] args) throws InterruptedException {
    final CountDownLatch countDownLatch = new CountDownLatch(totalCount);
    final Semaphore semaphore = new Semaphore(totalCurrency);
    ExecutorService executorService = Executors.newCachedThreadPool();
    for (int i = 0; i < totalCount; i++) {
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    semaphore.acquire();
                    //本身线程不安全
                    count++;
                    semaphore.release();
                    countDownLatch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }
    //其他线程运行完成执行下面操作
    countDownLatch.await();
    executorService.shutdown();
    System.out.println(count);
}

线程安全：

 //总共请求次数10000次 数值给大点 不然效果不明显
    private static int totalCount = 10000;
    //最大并发数 100个 数值给大点 不然效果不明显
    private static int totalCurrency = 100;
//    private static int count = 0;
    //使用原子类修饰
    private static AtomicInteger atomicInteger = new AtomicInteger(0);

    public static void main(String[] args) throws InterruptedException {

        final CountDownLatch countDownLatch = new CountDownLatch(totalCount);
        final Semaphore semaphore = new Semaphore(totalCurrency);
        ExecutorService executorService = Executors.newCachedThreadPool();
        for (int i = 0; i < totalCount; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    atomicInteger.incrementAndGet();
                    semaphore.release();
                    countDownLatch.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            });
        }
        //其他线程完成各自任务 countDownLatch.count==0
        countDownLatch.await();
        executorService.shutdown();
        System.out.println(atomicInteger);

    }