线程安全-并发容器

@Slf4j
@ThreadSafe
public class CopyOnWriteArrayListExample {

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

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

    private static CopyOnWriteArrayList<Integer> list = new CopyOnWriteArrayList<>();

    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++) {
            final int count = i;
            executorService.execute(() -> {
                try {
                    semaphore.acquire();
                    update(count);
                    semaphore.release();
                } catch (Exception e) {
                    log.error("exception", e);
                }
                countDownLatch.countDown();
            });
        }
        countDownLatch.await();
        executorService.shutdown();
        log.info("size:{}", list.size());
    }

    private static void update(int i) {
        list.add(i);
    }
}

线程安全：CopyOnWriteArrayList(写操作时先加锁，再创建新list，然后拷贝回原来数组，尽量使用于读多写少的操作中，读操作同arraylist)、

add，remove操作时线程安全的；
在并发环境下，addAll removeAll 不能保证整个的原子操作，只能保证每一次操作是原子性的，整个操作有可能被其他线程打断，需要手动加锁解决

1. ConcurrentSkipListMap和ConcurrentHashMap的区别：
2. ConcurrentHashMap在不高线程并发下性能比ConcurrentSkipListMap较好
3. ConcurrentSkipListMap在高并发下性能更好，且key是有序的