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java读写锁实现数据同步访问
锁机制最大的改进之一就是ReadWriteLock接口和它的唯一实现类ReentrantReadWriteLock。这个类有两个锁，一个是读操作锁，另一个是写操作锁。使用读操作锁时可以允许多个线程同时访问，但是使用写操作锁时只允许一个线程进行。在一个线程执行写操作时，其他线程不能够执行读操作。
下面我们将通过范例学习如何使用ReadWriteLock接口编写程序。这个范例将使用ReadWriteLock接口控制对价格对象的访问，价格对象存储了两个产品的价格。
1. 创建一个价格信息类PricesInfo，并且存放两个产品的价格。
import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;public class PricesInfo { //两个价格 private double price1; private double price2; //声明读写锁ReadWriteLock对象lock private ReadWriteLock lock; public PricesInfo(){ price1 = 1.0; price2 = 2.0; lock = new ReentrantReadWriteLock(); } public double getPrice1(){ lock.readLock().lock(); double value = http://www.mamicode.com/price1;>2. 创建读取类Reader，它实现了Runnable接口。
public class Reader implements Runnable { private PricesInfo pricesInfo; public Reader(PricesInfo pricesInfo){ this.pricesInfo = pricesInfo; } @Override public void run() { // 循环读取连个价格10次 for(int i=0;i<10;i++){ System.out.printf("%s: Price1: %f\n", Thread.currentThread().getName(), pricesInfo.getPrice1()); System.out.printf("%s: Price2: %f\n", Thread.currentThread().getName(), pricesInfo.getPrice2()); } }}3. 创建写入类Writer，它实现了Runnable接口。
public class Writer implements Runnable { private PricesInfo pricesInfo; public Writer(PricesInfo pricesInfo){ this.pricesInfo = pricesInfo; } @Override public void run() { // 循环修改两个价格3次 try { 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.println("Writer: Prices have been modified."); Thread.sleep(2); } } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } }}4. 创建范例的主类Main
public class Main { 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(); }}5. 程序运行结果如下
Thread-1: Price1: 1.000000Thread-4: Price1: 1.000000Thread-2: Price1: 1.000000Thread-2: Price2: 2.000000Thread-2: Price1: 1.000000Thread-2: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-0: Price1: 1.000000Thread-0: Price2: 2.000000Thread-2: Price1: 1.000000Thread-2: Price2: 2.000000Writer: Attempt to modify the prices.Writer: Prices have been modified.Thread-3: Price1: 1.000000Thread-3: Price2: 4.840562Thread-1: Price2: 2.000000Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Thread-1: Price1: 6.220535Thread-1: Price2: 4.840562Writer: Attempt to modify the prices.Writer: Prices have been modified.Thread-4: Price2: 2.000000Thread-4: Price1: 5.640719Thread-4: Price2: 1.872038Thread-4: Price1: 5.640719Thread-4: Price2: 1.872038Thread-2: Price1: 6.220535Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-2: Price1: 5.640719Thread-2: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Thread-3: Price1: 5.640719Thread-3: Price2: 1.872038Writer: Attempt to modify the prices.Writer: Prices have been modified.Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420Thread-4: Price1: 5.491746Thread-4: Price2: 2.729420
java读写锁实现数据同步访问
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