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();        }

    }}－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－－

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;    }}