基本概念

維護了一對鎖,read lock 可以由多個執行緒執行,只要沒有作者那麼write lock就是獨家的

簡單例子

package com.jie.rw;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockDemo {
    public static void main(String[] args) {
        MyCache myCache=new MyCache();

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

        //讀取
        for (int i = 1; i <= 5; i++) {
            final int temp=i;
            new Thread(()->{
                myCache.get(temp+"");
            },String.valueOf(i)).start();
        }
    }
}
class MyCache{
    private volatile Map<String,Object> map=new HashMap<>();
    //讀寫鎖
    ReentrantReadWriteLock lock=  new ReentrantReadWriteLock();
    //模擬寫
    public void put(String key,Object value){
        lock.writeLock().lock();
        try{
            System.out.println(Thread.currentThread().getName()+"寫入"+key);
            map.put(key,value);
            System.out.println(Thread.currentThread().getName()+"寫入完畢");
        }
        catch (Exception e){
            e.printStackTrace();
        }
        finally {
            lock.writeLock().unlock();
        }
    }
    //模擬讀
    public void get(String key){
        lock.readLock().lock();
        try{
            System.out.println(Thread.currentThread().getName()+"讀取"+key);
            Object o=map.get(key);
            System.out.println(Thread.currentThread().getName()+"讀取完畢");
        }
        catch (Exception e){
            e.printStackTrace();
        }
        finally {
            lock.readLock().unlock();
        }
    }
}
 

執行可以看到寫入是一個一個寫完 但是讀取可以插隊