程序员：并发下如何保证共享变量安全且不用锁？！

/**
 * @ClassName Cup
 * @Description 杯子 非线程安全
 * @Author MySelf
 * @Date 2019/9/25 21:28
 * @Version 1.0
 **/
public class Cup {

    //直径
    private double diameter;

    //高度
    private double height;

    public double getDiameter() {
        return diameter;
    }

    public double getHeight() {
        return height;
    }

    //非原子操作
    public void setCup(double diameter,double height){
        this.diameter = diameter;
        this.height = height;
    }
}

/**
 * @ClassName Cup
 * @Description 不可变对象，线程安全
 * @Author MySelf
 * @Date 2019/9/25 21:32
 * @Version 1.0
 **/
public final class Cup {

    private final double diameter;

    private final double height;

    public Cup(double diameter,double height){
        this.diameter = diameter;
        this.height = height;
    }

}

/**
 * @ClassName MoldAdapter
 * @Description 模具适配器
 * @Author MySelf
 * @Date 2019/9/25 21:35
 * @Version 1.0
 **/
public class MoldAdapter {
    
    private Map<String,Cup> cupMap = new ConcurrentHashMap<String, Cup>();

    public void updateCup(String version,Cup newCup){
        cupMap.put(version, newCup);
    }

}

/**
 * @ClassName DollMachineInfo
 * @Description 娃娃机不可变对象
 * @Author MySelf
 * @Date 2019/9/25 21:51
 * @Version 1.0
 **/
public final class DollMachineInfo {

    //编号
    private final String number;

    //支付二维码url
    private final String url;

    //机械手频率
    private final int frequency;

    public DollMachineInfo(String number,String url,int frequency){
        this.number = number;
        this.url = url;
        this.frequency = frequency;
    }

    public DollMachineInfo(DollMachineInfo dollMachineInfoType){
        this.number = dollMachineInfoType.number;
        this.url = dollMachineInfoType.url;
        this.frequency = dollMachineInfoType.frequency;
    }

    public String getNumber() {
        return number;
    }

    public String getUrl() {
        return url;
    }

    public int getFrequency() {
        return frequency;
    }
}

/**
 * @ClassName MachineRouter
 * @Description 机器信息表
 * @Author MySelf
 * @Date 2019/9/25 21:57
 * @Version 1.0
 **/
public final class MachineRouter {
    //保证其在并发环境的内存可见性
    private static volatile MachineRouter instance = new MachineRouter();
    //code与机器之间的映射关系
    private final Map<String,DollMachineInfo> routeMap;

    // 2、存储不可变量routeMap
    public MachineRouter(){
        //将数据库表中的数据加载到内存，存为Map
        this.routeMap = MachineRouter.setRouteFromeDB();
    }

    // 3、从db将数据存入Map
    private static Map<String, DollMachineInfo> setRouteFromeDB(){
        Map<String, DollMachineInfo> map = new HashMap<String, DollMachineInfo>();
        //DB 代码
        return map;
    }

    // 1、初始化实例
    public static MachineRouter getInstance(){
        return instance;
    }

    /**
     * 根据code获取对应的机器信息
     * @param code 对应编码
     * @return 机器信息
     */
    public DollMachineInfo getMacheine(String code){
        return routeMap.get(code);
    }

    /**
     * 修改当前MachineRouter实例
     * @param newInstance 新的实例
     */
    public static void setInstance(MachineRouter newInstance){
        instance = newInstance;
    }


    private static Map<String, DollMachineInfo> deepCopy(Map<String,DollMachineInfo> d){
        Map<String, DollMachineInfo> result = new HashMap<String, DollMachineInfo>();
        for (String key : d.keySet()){
            result.put(key, new DollMachineInfo(d.get(key)));
        }
        return result;
    }


    public Map<String, DollMachineInfo> getRouteMap() {
        //防御性复制
        return Collections.unmodifiableMap(deepCopy(routeMap));
    }
}

/**
 * @ClassName Worker
 * @Description 通讯对接类
 * @Author MySelf
 * @Date 2019/9/25 22:13
 * @Version 1.0
 **/
public class Worker extends Thread {

    @Override
    public void run(){
        boolean isRouterModification = false;
        String updateMachineInfo = null;
        while (true){
            //其余业务代码
            /**
             * 在通讯的Socket信息中解析，并更新数据表信息，再重置MachineRouter实例
             */
            if (isRouterModification){
                if ("DollMachineInfo".equals(updateMachineInfo)){
                    MachineRouter.setInstance(new MachineRouter());
                }
            }
            //其余业务代码
        }
    }

}