读写锁

package unsafe;

import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * @author klr
 * @create 2020-07-27-15:48
 */
public class RWL {
    public static void main(String[] args) {
//        MyCache myCache = new MyCache();
        MyCacheLock myCache = new MyCacheLock();
        //写入
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                myCache.put(temp+"",temp+"");
            },String.valueOf(i)).start();
        }

        //读取
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                myCache.get(temp+"");
            },String.valueOf(i)).start();
        }
    }
}

//自定义缓存，不加锁时
class MyCache{

    private volatile Map<String,Object> map = new HashMap<>();//保证可见性

    //写
    public void put(String s, Object o){
        System.out.println(Thread.currentThread()+"开始写"+s);
        map.put(s,o);
        System.out.println(Thread.currentThread()+"写完");
    }

    //读
    public void get(String s){
        System.out.println(Thread.currentThread()+"读到"+map.get(s));
        System.out.println(Thread.currentThread()+"读完");
    }
}

//使用读写锁，更加细粒度的操作
class MyCacheLock{

    private volatile Map<String,Object> map = new HashMap<>();//保证可见性

    private ReadWriteLock lock = new ReentrantReadWriteLock();


    //写入的时候只希望同时只有一个线程写
    public void put(String s, Object o){
        lock.writeLock().lock();
        System.out.println(Thread.currentThread()+"开始写"+s);
        map.put(s,o);
        System.out.println(Thread.currentThread()+"写完");
        lock.writeLock().unlock();
    }

    //读
    public void get(String s){
        lock.readLock().lock();
        System.out.println(Thread.currentThread()+"读到"+map.get(s));
        System.out.println(Thread.currentThread()+"读完");
        lock.readLock().unlock();
    }
}