使用volatile简单实现happen-before功能

首先解释appen-before，其作用就是保证两个操作的顺序性，特别是多线程中，确保数据的准确性，对于执行顺序会有一定的要求

这里引入volatile手动设置

类似的synchronized也可以实现happen-before

测试代码

package com.java.test.happer.before.volatiles;

/**
 * @Description:
 * @Author: Yourheart
 * @Create: 2022/11/3 22:54
 */
public class VolatileTest {


    int x = 0;
    volatile int y = 0;
    int a = 0;
    int b = 0;

    public void set() {
        a = 1;
        x = b;
    }

    public int get() {
        b = 1;
        y = a;
        return y;
    }

    @Override
    public String toString() {
        return "VolatileTest{" +
                "x=" + x +
                ", y=" + y +
                ", a=" + a +
                ", b=" + b +
                '}';
    }
}

package com.java.test.happer.before.volatiles;

import lombok.extern.slf4j.Slf4j;

/**
 * @Description:
 * @Author: Yourheart
 * @Create: 2022/11/3 23:24
 */
@Slf4j
public class ThreadDemoOne implements Runnable {

    private VolatileTest volatileTest;

    public ThreadDemoOne(VolatileTest volatileTest) {
        this.volatileTest = volatileTest;
    }

    @Override
    public void run() {
        this.volatileTest.set();
        log.info("【线程一】volatileTest:{}",volatileTest.toString());
    }
}

package com.java.test.happer.before.volatiles;

import lombok.extern.slf4j.Slf4j;

/**
 * @Description:
 * @Author: Yourheart
 * @Create: 2022/11/3 23:25
 */
@Slf4j
public class ThreadDemoTwo implements Runnable {


    private VolatileTest volatileTest;

    public ThreadDemoTwo(VolatileTest volatileTest) {
        this.volatileTest = volatileTest;
    }

    @Override
    public void run() {
        int i = this.volatileTest.get();
        log.info("获取到的y的数据:{}",i);
        log.info("【线程二】volatileTest:{}",volatileTest.toString());

    }
}

package com.java.test.happer.before.volatiles;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

/**
 * @Description:
 * @Author: Yourheart
 * @Create: 2022/11/3 23:28
 */
public class ThreadPoolExecutorDemo {
    /**
     * 核心线程数
     */
    static int corePoolSize = 3;
    /**
     * 最大线程数
     */
    static int maximumPoolSize = 6;
    /**
     * 超过 corePoolSize 线程数量的线程最大空闲时间
     */
    static long keepAliveTime = 2;
    /**
     * 以秒为时间单位
     */
    static TimeUnit unit = TimeUnit.SECONDS;
    /**
     * 创建工作队列，用于存放提交的等待执行任务
     */
    static BlockingQueue<Runnable> workQueue = new ArrayBlockingQueue<Runnable>(2);

    static ThreadPoolExecutor threadPoolExecutor = null;

    private static void initThreadPool() {
        threadPoolExecutor = new ThreadPoolExecutor(corePoolSize,
                maximumPoolSize,
                keepAliveTime,
                unit,
                workQueue,
                new ThreadPoolExecutor.AbortPolicy());
    }

    public static void executed(Runnable runnable){
        if (threadPoolExecutor==null){
            initThreadPool();
        }
        threadPoolExecutor.execute(runnable);
    }
}

package com.java.test.happer.before.volatiles;

import lombok.extern.slf4j.Slf4j;
import org.junit.Test;

/**
 * @Description:
 * @Author: Yourheart
 * @Create: 2022/11/3 23:27
 */
@Slf4j
public class ThreadTest {


    @Test
    public void test(){
       while (true){
           try {
               Thread.sleep(2000);
           } catch (InterruptedException e) {
               e.printStackTrace();
           }
           VolatileTest volatileTest=new VolatileTest();
           ThreadPoolExecutorDemo.executed(new ThreadDemoOne(volatileTest));
           ThreadPoolExecutorDemo.executed(new ThreadDemoTwo(volatileTest));

       }
    }
}

　　pom文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.java</groupId>
    <artifactId>test-study</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.2.1.RELEASE</version>
        <relativePath/>
    </parent>

    <dependencies>
        <!--tomcat容器-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--lombok依赖-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.16</version>
        </dependency>
        <!--引入junit单元测试依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <!--判断空的用法  -->
        <dependency>
            <groupId>commons-lang</groupId>
            <artifactId>commons-lang</artifactId>
            <version>2.6</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/com.oracle.database.jdbc/ojdbc8 -->
        <dependency>
            <groupId>com.oracle.database.jdbc</groupId>
            <artifactId>ojdbc8</artifactId>
            <version>12.2.0.1</version>
        </dependency>
        <!--springboot整合mybatis-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.2</version>
        </dependency>

        <!--添加fastjson依赖-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.70</version>
        </dependency>
        <!-- 热部署模块 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional> <!-- 这个需要为 true 热部署才有效 -->
        </dependency>
    </dependencies>


    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
        <finalName>study</finalName>
    </build>


</project>

　　在单线程中，执行顺序即使有变化，最终结果不会错乱，但是多线程中就会出现数据错乱的问题