为什么操作一个对象中的AtomicInteger不是原子操作

Question

代码如下：
import com.dcy.pojo.Prize;
import java.util.ArrayList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicInteger;

public class TestPrize {
static AtomicInteger atomicInteger = new AtomicInteger(30);
static AtomicInteger atomicInteger1 = new AtomicInteger(0);

static ExecutorService pool = Executors.newFixedThreadPool(5);
static ArrayList<Prize> prizes = new ArrayList<>();
public static void main(String[] args) throws InterruptedException {
    Prize p = new Prize();
    p.setActId(74);
    p.setSiteId(1001l);
    p.setPrizeLeft(30);
    prizes.add(p);
    for (int i=0;i<100;i++) {
       pool.execute(new TestCAS());
    }
    Thread.sleep(3000);
    System.out.println("atomicInteger1="+atomicInteger1.get());
}
static class TestCAS implements Runnable {
    @Override
    public void run() {
        for (Prize prize : prizes) {
            if (prize.getActId()==74) {
                int left =-1;
                if( (left=prize.getPrizeLeft().decrementAndGet())>=0){
                    atomicInteger1.incrementAndGet();
                    System.out.println("atomicInteger:"+atomicInteger.decrementAndGet()+"---"+Thread.currentThread().getName()+"left="+left);
                    prize.setPrizeLeft(left);
                }
            }
        }
    }
}

}
代码最后打印出来的atomicInteger1 多半都大于30，并且注意到left有多次打印重复的情况。为什么prize.getPrizeLeft().decrementAndGet()会返回相同的值？

Answer 1

在Prize中给prizeLeft属性加上volatile关键字也不行，必须得这样用
AtomicInteger prizeLeft = prize.getPrizeLeft();
if( (prizeLeft.decrementAndGet())>=0){
atomicInteger1.incrementAndGet();
才不会有问题