java 多线程 day12 读写锁

import java.util.Random;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
 * Created by chengtao on 17/12/5.
 * Lock 是替代 sycronized 的，而且sycronized无法实现读写锁
 */


public class Thread1201_ReadWriteLock {
    public static void main(String[] args) {
        final Queue3 q3 = new Queue3();
        for(int i=0;i<30;i++)
        {
            new Thread(){
                public void run(){
                    while(true){
                        q3.get();
                    }
                }

            }.start();

            new Thread(){
                public void run(){
                    while(true){
                        q3.put(new Random().nextInt(10000));
                    }
                }

            }.start();
        }

    }
}

class Queue3{
    private Object data = null;//共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据。
    ReadWriteLock rwl = new ReentrantReadWriteLock();
    public void get(){
        rwl.readLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + " 准备去读 ----- 数据!");
            Thread.sleep((long)(Math.random()*10));
            System.out.println(Thread.currentThread().getName() + " 已经读到 ----- 数据 :" + data);
            System.out.println();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally{
            rwl.readLock().unlock();
        }
    }

    public void put(Object data){

        rwl.writeLock().lock();
        try {
            System.out.println(Thread.currentThread().getName() + " 准备去写数据 !");
            Thread.sleep((long)(Math.random()*1000));
            this.data = data;
            System.out.println(Thread.currentThread().getName() + " 已经写入数据 : " + data);
            System.out.println();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally{
            rwl.writeLock().unlock();
        }


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

/**
 * Created by chengtao on 17/12/5.
 */
public class Thread1202_ReadWriteLock_Cache {
    private Map<String, Object> cache = new HashMap<String, Object>();
    public static void main(String[] args) {

    }

    //读写锁在缓存中的应用
    private ReadWriteLock rwl = new ReentrantReadWriteLock();
    public  Object getData(String key){
        rwl.readLock().lock();
        Object value = null;
        try{
            value = cache.get(key);
            if(value == null){
                rwl.readLock().unlock();
                rwl.writeLock().lock();
                try{
                    if(value==null){
                        value = "aaaa";//实际失去queryDB();
                    }
                }finally{
                    rwl.writeLock().unlock();
                }
                rwl.readLock().lock();
            }
        }finally{
            rwl.readLock().unlock();
        }
        return value;
    }
}