JDK5.0 特性-线程 Condition

来自：http://www.cnblogs.com/taven/archive/2011/12/17/2291471.html

 import java.util.concurrent.ExecutorService;

 import java.util.concurrent.Executors;

 import java.util.concurrent.locks.Condition;

 import java.util.concurrent.locks.Lock;

 import java.util.concurrent.locks.ReentrantLock;

 /**

  *有时候线程取得lock后需要在一定条件下才能做某些工作，比如经典的Producer和Consumer问题

  *在Java 5.0以前，这种功能是由Object类的wait(),notify()和notifyAll()等方法实现的

  *在5.0里面，这些功能集中到了Condition这个接口实现

  */

 /**

  * 使用Condition的关键技术点如下:

  * 1.通过Lock的newCondition方法创建Condition的对象

  * 2.Condition的await方法使当前线程进入等待状态,并且释放它占据的Lock,直到有其他的线程唤醒当前线程时,重新占有Lock.

  * 3.Condition的signal方法唤醒其他正在等待该Condition的线程.

  */

 public class ConditionTest {

     /**

      * 篮子程序，这里为了简化问题，篮子中最多只能有一个苹果

      * Consumer必须在篮子里有苹果的时候才能吃苹果，否则它必须暂时放弃对篮子的锁定

      * 等到Producer往篮子里放了苹果后再去拿来吃。

      * 否则它也需要暂时解锁等Comsumer把苹果吃了才能往篮子里放苹果。

      */

     public static class Basket{

         //锁

         Lock lock = new ReentrantLock();

         //根据锁产生Condition对象

         Condition produced = lock.newCondition();

         Condition consumed  = lock.newCondition();

         //篮子里的苹果数，最多为1

         int num = 0;

         //生产苹果，往篮子里放

         public void produce() throws InterruptedException{

             //获得锁

             lock.lock();

             System.out.println("Producer get a lock...");

                      try{

                 //判断是否满足生产条件

                 while(num == 1){

                     //如果有苹果，则不生产，放弃锁，进入睡眠

                     //等待消费者消费

                     System.out.println("Producer sleep...");

                     consumed.await();

                     System.out.println("Producer awaked...");

                 }

                 //生产苹果

                 Thread.sleep(500);

                 System.out.println("Producer produced an Apple.");

                 num = 1;

                 //通知等待produced Condition的线程

                 produced.signal();

             }finally{

                 lock.unlock();

             }

         }

         //消费苹果，从篮子里取

         public void consume() throws InterruptedException{

             //获得锁

             lock.lock();

             System.out.println("Consumer get a lock...");

             try{

                 //判断是否满足消费条件

                 while(num == 0){

                     //如果没有苹果，无法消费，则放弃锁，进入睡眠

                     //等待生产者生产苹果

                     System.out.println("Consumer sleep...");

                     produced.await();

                     System.out.println("Consumer awaked...");

                 }

                 //吃苹果

                 Thread.sleep(500);

                 System.out.println("Consumer consumed an Apple.");

                 num = 0;

                 //发信号唤醒某个等待consumed Condition的线程

                             consumed.signal();

             } finally {

                 lock.unlock();

             }

         }

     }

     //测试Basket程序

     public static void testBasket() throws Exception{

         final Basket basket = new Basket();

         //定义一个producer

         Runnable producer  = new Runnable(){

             public void run() {

                 try{

                     basket.produce();

                 }catch(InterruptedException ex){

                     ex.printStackTrace();

                 }

             }           

         };

         //定义一个consumer

         Runnable consumer = new Runnable(){

             public void run(){

                 try{

                     basket.consume();

                 }catch(InterruptedException ex){

                     ex.printStackTrace();

                 }

             }

         };

         //各生产3个consumer和producer

         ExecutorService service = Executors.newCachedThreadPool();

         for(int i = 0; i <3; i++){

             service.submit(producer);

         }

         for(int i = 0;i<3;i++){

             service.submit(consumer);

         }

         service.shutdown();

     }

     public static void main(String... args)throws Exception{

         ConditionTest.testBasket();

     }

 }