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();
	}
}