Java多线程之~~~ReadWriteLock 读写分离的多线程实现

在多线程开发中，经常会出现一种情况，我们希望读写分离。就是对于读取这个动作来说，可以同时有多个线程同

时去读取这个资源，但是对于写这个动作来说，只能同时有一个线程来操作，而且同时，当有一个写线程在操作这个资

源的时候，其他的读线程是不能来操作这个资源的，这样就极大的发挥了多线程的特点，能很好的将多线程的能力发挥

出来。

在Java中，ReadWriteLock这个接口就为我们实现了这个需求，通过他的实现类ReentrantReadWriteLock我们可

以很简单的来实现刚才的效果，下面我们使用一个例子来说明这个类的用法。

 package com.bird.concursey.charpet3;

 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;

 public class PricesInfo {

     private double price1;

     private double price2;

     private ReadWriteLock lock;

     public PricesInfo() {
         price1 = 1.0;
         price2 = 2.0;
         lock = new ReentrantReadWriteLock();
     }

     public double getPrice1() {
         //读取资源锁定
         lock.readLock().lock();
         double value = price1;
         lock.readLock().unlock();
         return value;
     }

     public double getPrice2() {
         lock.readLock().lock();
         double value = price2;
         lock.readLock().unlock();
         return value;
     }

     public void setPrices(double price1, double price2) {
         lock.writeLock().lock();
         this.price1 = price1;
         this.price2 = price2;
         lock.writeLock().unlock();
     }


 }

下面是读和写两个不同的类

 package com.bird.concursey.charpet3;

 public class Reader implements Runnable {

     private PricesInfo pricesInfo;

     public Reader(PricesInfo pricesInfo) {
         this.pricesInfo = pricesInfo;
     }

     @Override
     public void run() {
         for (int i = 0; i < 10; i++) {
             System.out.printf("%s: Price 1: %f\n", Thread.currentThread()
                     .getName(), pricesInfo.getPrice1());
             System.out.printf("%s: Price 2: %f\n", Thread.currentThread()
                     .getName(), pricesInfo.getPrice2());
         }
     }

 }

 package com.bird.concursey.charpet3;

 public class Writer implements Runnable {

     private PricesInfo pricesInfo;

     public Writer(PricesInfo pricesInfo) {
         this.pricesInfo = pricesInfo;
     }

     @Override
     public void run() {
         for (int i = 0; i < 3; i++) {
             System.out.printf("Writer: Attempt to modify the prices.\n");
             pricesInfo.setPrices(Math.random() * 10, Math.random( ) * 8);
             System.out.printf("Writer: Prices have been modified.\n");
             try {
                 Thread.sleep(2);
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }
         }
     }

     public static void main(String[] args) {
         PricesInfo pricesInfo = new PricesInfo();
         Reader readers[] = new Reader[5];
         Thread threadsReader[] = new Thread[5];
         for (int i = 0; i < 5; i++){
             readers[i] = new Reader(pricesInfo);
             threadsReader[i] = new Thread(readers[i]);
         }
         Writer writer = new Writer(pricesInfo);
         Thread threadWriter = new Thread(writer);
         for (int i = 0; i < 5; i++){
             threadsReader[i].start();
         }
         threadWriter.start();
     }
 }