ReadWriteLock

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/*
独占锁（写锁） 一次只能被一个线程占用
共享锁（读锁） 多个线程可以同时占有
读-读 可以共存
读-写 不能共存
写-写 不能共存
 */
public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache myCache = new MyCache();
        for (int i = 1; i <= 5; i++) {
            final int tmp = i;
            new Thread(()->{
                myCache.put(tmp + "", tmp + "");
            }, String.valueOf(i)).start();
        }

        for (int i = 1; i <= 5; i++) {
            final int tmp = i;
            new Thread(()->{
                myCache.get(tmp + "");
            }, String.valueOf(i)).start();
        }
    }
}

class MyCache{
    private volatile Map<String, Object> map = new HashMap<>();
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();

    public void put(String key, Object value){
        readWriteLock.writeLock().lock();
        try{
            System.out.println(Thread.currentThread().getName() + "写入" + key);
            map.put(key, value);
            System.out.println(Thread.currentThread().getName() + "写入完毕");
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            readWriteLock.writeLock().unlock();
        }
    }

    public void get(String key){
        readWriteLock.readLock().lock();
        try{
            System.out.println(Thread.currentThread().getName() + "读取" + key);
            map.get(key);
            System.out.println(Thread.currentThread().getName() + "读取完毕");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            readWriteLock.readLock().unlock();
        }
    }
}