JAVA 读写锁ReentrantReadWriteLock()

package com.test.rw;

import java.util.HashMap;
import java.util.Hashtable;
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有
  共享锁(读锁) 多规格线程可以同时占有
  ReadWriteLock
  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) {
    
    
        MyCache2 myCache = new MyCache2();
        for (int i = 1; i <=5 ; i++) {
    
    
            final int temp = i;
            new Thread(()->{
    
    
                myCache.put(temp+ "",temp+ "");
            },String.valueOf(i)).start();
        }

        for (int i = 1; i <=5 ; i++) {
    
    
            final int temp = i;
            new Thread(()->{
    
    
                myCache.get(temp + "");
            },String.valueOf(i)).start();
        }
    }
}
// 加锁的
class MyCache2 {
    
    
    private volatile Map<String,Object> map = new HashMap<>();
    // 读写锁  更加细粒度的控制
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    // 存，写入的时候，只希望同时只有一个线程写
    public void put(String key,Object value){
    
    
        readWriteLock.writeLock().lock();
        try {
    
    
            System.out.println(Thread.currentThread().getName() + "write key :" + key);
            map.put(key,value);
            System.out.println(Thread.currentThread().getName() + "write Ok");
        }catch (Exception e){
    
    
            e.getStackTrace();
        }finally {
    
    
            readWriteLock.writeLock().unlock();
        }
    }
    // 取，读，所有人都可以读
    public void get(String key){
    
    
        readWriteLock.readLock().lock();
        try {
    
    
            System.out.println(Thread.currentThread().getName() + "Read key " + key);
            map.get(key);
            System.out.println(Thread.currentThread().getName() + "Read Ok");
        }catch (Exception e){
    
    
            e.getStackTrace();
        }finally {
    
    
            readWriteLock.readLock().unlock();
        }

    }

}

// 无锁的
class MyCache {
    
    
    private volatile Map<String,Object> map = new HashMap<>();

    public void put(String key,Object value){
    
    
        System.out.println(Thread.currentThread().getName() + "write key :" + key);
        map.put(key,value);
        System.out.println(Thread.currentThread().getName() + "write Ok");
    }

    public void get(String key){
    
    
        System.out.println(Thread.currentThread().getName() + "Read key " + key);
        map.get(key);
        System.out.println(Thread.currentThread().getName() + "Read Ok");
    }

}