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
原文地址：http://www.cnblogs.com/q202105271618/p/16856219.html
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