线程安全测试--共享nacos配置--线程池定时心跳

CopyOnWriteArrayList集合
是一个线程安全的List集合,允许多个线程执行并发更新,但是只能有一个更新成功

双重校验锁机制：

package com.jt.common.thread;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Vector;
import java.util.concurrent.CopyOnWriteArrayList;

public class SyncTests {
    //private static List cache=new Vector<>();
    //CopyOnWriteArrayList是一个线程安全的List集合,允许多个线程执行并发更新,但是只能有一个更新成功.
    private static List cache=new CopyOnWriteArrayList<>();//CAS(比较和交换)

    //    public synchronized static List selectAll(){
//        if (cache.isEmpty()) {
//              System.out.println("Get Data From Database");
//              List data = Arrays.asList("A", "B", "C");
//              cache.addAll(data);
//        }
//        return cache;
//    }
    public static List selectAll(){
        if(cache.isEmpty()) {//A,B,C,D
            synchronized (cache) {
                if (cache.isEmpty()) {
                    System.out.println("Get Data From Database");
                    List data = Arrays.asList("A", "B", "C");
                    cache.addAll(data);
                }
            }
        }
        return cache;
    }

    public static void main(String[] args) {
        //System.out.println(Thread.currentThread().getName());
        Thread t1=new Thread(){
            @Override
            public void run() {
                System.out.println(selectAll());
            }
        };
        Thread t2=new Thread(){
            @Override
            public void run() {
                System.out.println(selectAll());
            }
        };
        Thread t3=new Thread(){
            @Override
            public void run() {
                System.out.println(selectAll());
            }
        };
        Thread t4=new Thread(){
            @Override
            public void run() {
                System.out.println(selectAll());
            }
        };
        Thread t5=new Thread(){
            @Override
            public void run() {
                System.out.println(selectAll());
            }
        };
        t1.start();
        t2.start();
        t3.start();
        t4.start();
        t5.start();
    }
}

双层锁保证本地缓存安全

@RefreshScope
@RestController
public class ProviderCacheController {
    @Value("${useLocalCache:false}")
    private boolean useLocalCache;

    @RequestMapping("/provider/cache01")
    public String doUseLocalCache01() {
        return "useLocalCache'value is   " + useLocalCache;
    }

    //---------------------------------------------------------
    //构建一个本地(Local)缓存对象(基于jvm中的一个对象存储从数据库获取的数据).
    private List cache = new ArrayList<>();

    @RequestMapping("/provider/cache02")
    public List doUseLocalCache02() {
        if (cache.isEmpty()) {
            synchronized (cache) {
                if (cache.isEmpty()) {//Thread-A,Thread-B,...
                    System.out.println("==Get data from database==");
                    //假设这部分分类信息是从数据库获取的,但是,我不希望每次获取分类信息都要从数据库查
                    List cates = Arrays.asList("Category-A", "Category-B", "Category-C");
                    cache.addAll(cates);
                }
            }
        }
        return cache;
        }//生产层面
    }

共享nacos配置

server:
  port: 8081
spring:
  application:
    name: sca-provider
  cloud:
    nacos:
      discovery:
        server-addr: localhost:8848
      config:
        server-addr: localhost:8848 #配置中心地址
        file-extension: yml
        namespace: 67d8daf6-d1a2-4796-a367-bd54bd58bc7a
        group: DEFAULT_GROUP
        shared-configs[0]: #共享配置
          data-id: app-public.yml
          refresh: true

测试配置

@RefreshScope
@RestController
public class ProviderSecretController {
    @Value("${app.secret:123456}")
    private String secret;
    @GetMapping("/provider/secret")
    public String doGetSecret(){
        return "the secret is "+secret;
    }
}

基于ScheduledExecutorService对象完成
一个多线程的任务调度,在nacos注册中心发送定时心跳
以及nacos配置中心数据定时拉取(pull),底层都是通过
这个对象完成的.

public class ScheduledExecutorServiceUtils {
    public static void main(String[] args) {
        //......
        ScheduledExecutorService ses = Executors.newScheduledThreadPool(3);
        Runnable task=new Runnable() {
            @Override
            public void run() {
                String tName = Thread.currentThread().getName();
                System.out.println(tName+"->"+System.currentTimeMillis());
            }
        };
        ses.scheduleAtFixedRate(task,
                1,
                1,
                TimeUnit.SECONDS);
    }
}