并发问题演示

/**
 * 多次执行，每次count的值都不同，说明不支持并发
 */
public class ConcurrencyTest {

    public static int clientTotal = 5000;

    public static int threadTotal = 200;

    public static int count = 0;

    public static void main(String[] args) throws InterruptedException {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        CountDownLatch countDownLatch = new CountDownLatch(clientTotal);

        for (int i = 0; i < clientTotal; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    add();
                    semaphore.release();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        System.out.println("count:" + count);
    }

    private static void add() {
        count++;
    }
}