JAVA ReentrantReadWriteLock AND 缓存系统

package cn.itcast.hemai2;import java.util.Random;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;//notify和wait必须 在同步代码块里面写，而不能存在某个普通的代码或者代码块中。public class ReadWriteLockTest {public static void main(String[] args) {final Queue3 q3 = new Queue3();for(int i=0;i<3;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();}}}/** * 在写的情况 下就不能再读。 * @author admin * */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() + " be ready to read data!");Thread.sleep((long)(Math.random()*1000));System.out.println(Thread.currentThread().getName() + "have read data :" + data);} catch (InterruptedException e) {e.printStackTrace();}finally{rwl.readLock().unlock();}}public void put(Object data){rwl.writeLock().lock();try {System.out.println(Thread.currentThread().getName() + " be ready to write data!");Thread.sleep((long)(Math.random()*1000));this.data = data;System.out.println(Thread.currentThread().getName() + " have write data: " + data);} catch (InterruptedException e) {e.printStackTrace();}finally{rwl.writeLock().unlock();}}}

package cn.itcast.hemai2;import java.util.HashMap;import java.util.Map;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;public class CacheDemo {private Map<String, Object> cache = new HashMap<String, Object>();public static void main(String[] args) {// TODO Auto-generated method stub}/** * 读写互斥。多线程 并发读取，写读取互斥 。 */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;}}


	
				
	
				   		  
	  	   
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