longAdder.increment()比 atomicLon

为什么需要AtomicInteger原子操作类？

对于Java中的运算操作，例如自增或自减，若没有进行额外的同步操作，在多线程环境下就是线程不安全的。num++解析为num=num+1，明显，这个操作不具备原子性，多线程并发共享这个变量时必然会出现问题。测试代码如下:

/**
 * @description: 压测AtomicLong的原子操作性能
 */
public class AtomicLongTest implements Runnable {


    private static AtomicLong atomicLong = new AtomicLong(0);

    @Override
    public void run() {
        for (int i = 0; i < 10000; i++) {
            atomicLong.incrementAndGet();
        }
    }

    public static void main(String[] args) {
        ExecutorService es = Executors.newFixedThreadPool(30);
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            es.submit(new AtomicLongTest());
        }
        es.shutdown();
        //保证任务全部执行完
        while (!es.isTerminated()) { }
        long end = System.currentTimeMillis();
        System.out.println("AtomicLong add 耗时=" + (end - start));
        System.out.println("AtomicLong add result=" + atomicLong.get());
    }
}

/**
 * @description: 压测LongAdder的原子操作性能
 */
public class LongAdderTest implements Runnable{
    private static LongAdder longAdder = new LongAdder();

    @Override
    public void run() {
        for (int i = 0; i < 10000; i++) {
            longAdder.increment();
        }
    }

    public static void main(String[] args) {
        ExecutorService es = Executors.newFixedThreadPool(30);
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000; i++) {
            es.submit(new LongAdderTest());
        }
        es.shutdown();
        //保证任务全部执行完
        while (!es.isTerminated()) {
        }
        long end = System.currentTimeMillis();
        System.out.println("LongAdder add 耗时=" + (end - start));
        System.out.println("LongAdder add result=" + longAdder.sum());
    }

}

在高并发情况下，LongAdder(累加器)比AtomicLong原子操作效率更高，LongAdder累加器是java8新加入的，参考以下压测代码
https://blog.csdn.net/fanrenxiang/article/details/80623884