Java多線程之~~~ReadWriteLock 讀寫分離的多線程實現

在多線程開發中，常常會出現一種情況，我們希望讀寫分離。

就是對於讀取這個動作來說，能夠同一時候有多個線程同

時去讀取這個資源，可是對於寫這個動作來說，僅僅能同一時候有一個線程來操作。並且同一時候，當有一個寫線程在操作這個資

源的時候。其它的讀線程是不能來操作這個資源的。這樣就極大的發揮了多線程的特點。能非常好的將多線程的能力發揮

出來。

在Java中，ReadWriteLock這個接口就為我們實現了這個需求。通過他的實現類ReentrantReadWriteLock我們可

以非常easy的來實現剛才的效果，以下我們使用一個樣例來說明這個類的使用方法。

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() {
		//讀取資源鎖定
		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();
	}
	
	
}

以下是讀和寫兩個不同的類

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();
	}
}