AtomicInteger 并发加加

atomic并发加加    用的是硬件的cas  原子性操作 不会有并发问题  速度还快

下面的代码是从《深入理解java虚拟机弄出来的》

import java.util.concurrent.atomic.AtomicInteger;

public  class volatileTest {

    public static AtomicInteger race = new AtomicInteger();

    public static void increase(){
        race.incrementAndGet();
    }

    private static final int THREAD_COUNT = 20;

    public static void main(String[] args) throws InterruptedException {

        Thread[] threads = new Thread[THREAD_COUNT];

        for (int i = 0; i < THREAD_COUNT; i++) {
            threads[i] = new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0;i<10000;i++){
                        increase();
                    }
                }
            });

            threads[i].start();
        }

        System.out.println(Thread.activeCount());
//这里如果改打  结果就不准确了
        while (Thread.activeCount()>1){
            Thread.yield();
        }


        System.out.println(race);

    }
}

 

atomic并发加是准确的

我直接跑不准确是因为主线程跑完了，其他加的线程还没跑完
改为下面代码

import java.util.concurrent.atomic.AtomicInteger;

public  class volatileTest {

    public static AtomicInteger race = new AtomicInteger();

    public static void increase(){
        race.incrementAndGet();
    }

    private static final int THREAD_COUNT = 20;

    public static void main(String[] args) throws InterruptedException {

        Thread[] threads = new Thread[THREAD_COUNT];

        for (int i = 0; i < THREAD_COUNT; i++) {
            threads[i] = new Thread(new Runnable() {
                @Override
                public void run() {
                    for (int i = 0;i<10000;i++){
                        increase();
                    }
                }
            });

            threads[i].start();
        }

        System.out.println(Thread.activeCount());
        while (Thread.activeCount()>10){
            //这里如果加race  那么只会跑一次 不知道什么情况
            System.out.println("来了"+"此时是："+race);
            //System.out.println("来了"+"此时是：");
            Thread.yield();
        }


        System.out.println(race);
        Thread.sleep(200);
        System.out.println(race);
    }
}

　　

先这样吧 我的水平太差里