ExecutorService,Semaphore,CountDownLatch测是不是线程安全

public class StringExample1 {

    // 请求总数
    public static int clientTotal = 5000;

    // 同时并发执行的线程数
    public static int threadTotal = 200;

    public static StringBuilder stringBuilder = new StringBuilder();

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        final Semaphore semaphore = new Semaphore(threadTotal);
        final CountDownLatch countDownLatch = new CountDownLatch(clientTotal);
        for (int i = 0; i < clientTotal ; i++) {
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    //调用被测类的修改方法
                    update();
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
               
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        //打印结果
        log.info("size:{}", stringBuilder.length());
    }

    private static void update() {
        //被测的方法
        stringBuilder.append("1");
    }
}