JDK1.5中的多线程升级方案

JDK1.5中提供了多线程升级解决方案，将synchronized替换为了显示的Lock操作。将Object中的wait、notify、notifyAll替换为了condition对象（该对象可以通过Lock锁进行获取）。

有关Lock接口以及condition对象的详细介绍请查找官方API，这里不做详细介绍，我只是想通过两个例子来对比一下synchronized和Lock。

使用synchronized的生产者和消费者关系：

class Resource {// 产品名称private String name;// 计数器private int count = 0;// 标志位，标志 生产或消费private boolean flag = false;// 生产活动public synchronized void set(String name) {// 如果flag为true，则说明已经生产还未消费，使线程进入等待状态// 循环判断，线程被唤醒后也进行判断确保产品已经消费while (flag)try {wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}this.name = name + "---" + ++count;System.out.println(Thread.currentThread().getName() + "...生产者..."+ this.name);// 产品已生产，flag置为trueflag = true;// 唤醒所有线程this.notifyAll();}// 消费活动public synchronized void out() {// 如果flag为false，则说明还已经消费还未生产，使线程进入等待状态// 循环判断，线程被唤醒后也进行判断确保产品已经生产while (!flag)try {wait();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}System.out.println(Thread.currentThread().getName() + "...消费者..."+ this.name);// 产品已消费，flag置为falseflag = false;// 唤醒所有线程this.notifyAll();}}// 生产者class Producer implements Runnable {private Resource res;public Producer(Resource res) {this.res = res;}@Overridepublic void run() {// TODO Auto-generated method stubwhile (true) {res.set("++商品++");}}}// 消费者class Consumer implements Runnable {private Resource res;public Consumer(Resource res) {this.res = res;}@Overridepublic void run() {// TODO Auto-generated method stubwhile (true) {res.out();}}}public class ProducerConsumer {public static void main(String[] args) {// TODO Auto-generated method stubResource resource = new Resource();Producer producer = new Producer(resource);Consumer consumer = new Consumer(resource);Thread t1 = new Thread(producer);Thread t2 = new Thread(producer);Thread t3 = new Thread(consumer);Thread t4 = new Thread(consumer);t1.start();t2.start();t3.start();t4.start();}}

使用Lock锁的生产者和消费者关系：

import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;class Resource {// 产品名称private String name;// 计数器private int count;// 标志位，标志 生产或消费private boolean flag = false;// 创建Lock锁private Lock lock = new ReentrantLock();// 创建condition对象private Condition condition_pro = lock.newCondition();private Condition condition_Con = lock.newCondition();// 生产活动public void set(String name) {// 上锁lock.lock();try {// 如果flag为true，则说明已经生产还未消费，使线程进入等待状态// 循环判断，线程被唤醒后也进行判断确保产品已经消费while (flag)// 线程休眠condition_pro.await();this.name = name + "---" + ++count;System.out.println(Thread.currentThread().getName() + "...生产者..."+ this.name);// 产品已生产，flag置为trueflag = true;// 唤醒所有线程condition_Con.signalAll();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();} finally {// 解锁，该动作一定要执行lock.unlock();}}// 消费活动public void out() {// 上锁lock.lock();try {// 如果flag为false，则说明还已经消费还未生产，使线程进入等待状态// 循环判断，线程被唤醒后也进行判断确保产品已经生产while (!flag)// 线程休眠condition_Con.await();System.out.println(Thread.currentThread().getName() + "...消费者..."+ this.name);// 产品已消费，flag置为falseflag = false;// 唤醒所有线程condition_pro.signalAll();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();} finally {// 解锁，该动作一定要执行lock.unlock();}}}// 生产者class Producer implements Runnable {private Resource res;public Producer(Resource res) {this.res = res;}@Overridepublic void run() {// TODO Auto-generated method stubwhile (true) {res.set("++商品++");}}}// 消费者class Consumer implements Runnable {private Resource res;public Consumer(Resource res) {this.res = res;}@Overridepublic void run() {// TODO Auto-generated method stubwhile (true) {res.out();}}}public class ProducerConsumer {public static void main(String[] args) {// TODO Auto-generated method stubResource resource = new Resource();Producer producer = new Producer(resource);Consumer consumer = new Consumer(resource);Thread t1 = new Thread(producer);Thread t2 = new Thread(producer);Thread t3 = new Thread(consumer);Thread t4 = new Thread(consumer);t1.start();t2.start();t3.start();t4.start();}}

通过对比可以看出，一个Lock锁可以对应多个condition，解决了锁嵌套时出现的死锁现象。