java多线程编程——显示锁ReadWriteLock（二）

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当需要对集合同时进行写入和读取操作时，如果多线程同时操作会出现异常，那么现在利用ReadWriteLock显示锁，可以在写入量比较小，读取量比较大的场景中，方便的实现上述功能。

package test;import java.util.Calendar;import java.util.Map;import java.util.TreeMap;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantReadWriteLock;/** * 可重入读写锁 * * @author Administrator * */@SuppressWarnings("all")public class ReadWriteLockDemo {private ReentrantReadWriteLock lock = null;// 读锁private Lock readLock = null;// 写锁private Lock writeLock = null;public int key = 100;public int index = 100;// 线程共享数据public Map<Integer, String> dataMap = null;public ReadWriteLockDemo() {// 创建公平的可重入读写锁lock = new ReentrantReadWriteLock(true);readLock = lock.readLock();writeLock = lock.writeLock();dataMap = new TreeMap<Integer, String>();}public static void main(String[] args) {ReadWriteLockDemo test = new ReadWriteLockDemo();// 第一次获取写入锁test.writeLock.lock();System.out.println("线程" + Thread.currentThread().getName() + "第一次获取写入锁");// 第二次获取写入锁（这就是可重入的含义）test.writeLock.lock();System.out.println("线程" + Thread.currentThread().getName() + "第二次获取写入锁");test.readLock.lock();System.out.println("线程" + Thread.currentThread().getName() + "第一次获取读取锁");test.readLock.lock();System.out.println("线程" + Thread.currentThread().getName() + "第二次获取读取锁");test.readLock.lock();System.out.println("线程" + Thread.currentThread().getName() + "第三次获取读取锁");test.writeLock.unlock();test.writeLock.unlock();test.readLock.unlock();test.readLock.unlock();test.readLock.unlock();test.test();}public void test() {for (int i = 0; i < 10; i++) {new Thread(new reader(this)).start();}for (int i = 0; i < 3; i++) {new Thread(new writer(this)).start();}}public void read() {readLock.lock();try {if (dataMap.isEmpty()) {Calendar now = Calendar.getInstance();System.out.println("线程" + Thread.currentThread().getName() + "在" + now.getTime().getTime() + "读取数据，但是dataMap为空");}String value = dataMap.get(index);Calendar now = Calendar.getInstance();System.out.println("线程" + Thread.currentThread().getName() + "在" + now.getTime().getTime() + "读取数据，key=" + index + "，value=" + value + "，dataMap大小为" + dataMap.size());if (value != null) {index++;}} finally {readLock.unlock();}try {Thread.sleep(3000);} catch (Exception e) {e.printStackTrace();}}public void write() {writeLock.lock();try {String value = "value" + key;dataMap.put(new Integer(key), value);Calendar now = Calendar.getInstance();System.out.println("线程" + Thread.currentThread().getName() + "在" + now.getTime().getTime() + "写入数据，key=" + key + "，value=" + value + "，dataMap大小为" + dataMap.size());key++;try {Thread.sleep(500);} catch (Exception e) {e.printStackTrace();}} finally {writeLock.unlock();}}class reader implements Runnable {private ReadWriteLockDemo test = null;public reader(ReadWriteLockDemo test) {this.test = test;}@Overridepublic void run() {Calendar now = Calendar.getInstance();System.out.println("读取线程" + Thread.currentThread().getName() + "在" + now.getTime().getTime() + "开始执行");for (int i = 0; i < 10; i++) {test.read();}}}class writer implements Runnable {private ReadWriteLockDemo test = null;public writer(ReadWriteLockDemo test) {this.test = test;}@Overridepublic void run() {Calendar now = Calendar.getInstance();System.out.println("写入线程" + Thread.currentThread().getName() + "在" + now.getTime().getTime() + "开始执行");for (int i = 0; i < 10; i++) {test.write();}}}}

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