特殊的队列:BlockingQueue

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.BlockingQueue;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;



/**

    本例介绍一个特殊的队列:BlockingQueue,如果BlockQueue是空的,从BlockingQueue取东西的操作将会被阻断进入等待状态,直到BlockingQueue进了东西才会被唤醒.同样,如果BlockingQueue是满的,任何试图往里存东西的操作也会被阻断进入等待状态,直到BlockingQueue里有空间才会被唤醒继续操作.

    本例再次实现11.4线程----条件Condition中介绍的篮子程序,不过这个篮子中最多能放的苹果数不是1,可以随意指定.当篮子满时,生产者进入等待状态,当篮子空时,消费者等待.

*/

/**

    使用BlockingQueue的关键技术点如下:

    1.BlockingQueue定义的常用方法如下:

        1)add(anObject):把anObject加到BlockingQueue里,即如果BlockingQueue可以容纳,则返回true,否则招聘异常

        2)offer(anObject):表示如果可能的话,将anObject加到BlockingQueue里,即如果BlockingQueue可以容纳,则返回true,否则返回false.

        3)put(anObject):把anObject加到BlockingQueue里,如果BlockQueue没有空间,则调用此方法的线程被阻断直到BlockingQueue里面有空间再继续.

        4)poll(time):取走BlockingQueue里排在首位的对象,若不能立即取出,则可以等time参数规定的时间,取不到时返回null

        5)take():取走BlockingQueue里排在首位的对象,若BlockingQueue为空,阻断进入等待状态直到Blocking有新的对象被加入为止

    2.BlockingQueue有四个具体的实现类,根据不同需求,选择不同的实现类

        1)ArrayBlockingQueue:规定大小的BlockingQueue,其构造函数必须带一个int参数来指明其大小.其所含的对象是以FIFO(先入先出)顺序排序的.

        2)LinkedBlockingQueue:大小不定的BlockingQueue,若其构造函数带一个规定大小的参数,生成的BlockingQueue有大小限制,若不带大小参数,所生成的BlockingQueue的大小由Integer.MAX_VALUE来决定.其所含的对象是以FIFO(先入先出)顺序排序的

        3)PriorityBlockingQueue:类似于LinkedBlockQueue,但其所含对象的排序不是FIFO,而是依据对象的自然排序顺序或者是构造函数的Comparator决定的顺序.

        4)SynchronousQueue:特殊的BlockingQueue,对其的操作必须是放和取交替完成的.

    3.LinkedBlockingQueue和ArrayBlockingQueue比较起来,它们背后所用的数据结构不一样,导致LinkedBlockingQueue的数据吞吐量要大于ArrayBlockingQueue,但在线程数量很大时其性能的可预见性低于ArrayBlockingQueue.        

*/

public class BlockingQueueTest {

       /**定义装苹果的篮子*/

       public static class Basket{

              //篮子,能够容纳3个苹果

              BlockingQueue<String> basket = new ArrayBlockingQueue<String>(3);

              //生产苹果,放入篮子

              public void produce() throws InterruptedException{

                     //put方法放入一个苹果,若basket满了,等到basket有位置

                     basket.put("An apple");

              }

              //消费苹果,从篮子中取走

              public String consume() throws InterruptedException{

                     //take方法取出一个苹果,若basket为空,等到basket有苹果为止

                     return basket.take();

              }

       }

       //测试方法

       public static void testBasket(){

              final Basket basket = new Basket();//建立一个装苹果的篮子

              //定义苹果生产者

              class Producer implements Runnable{

                     public void run(){

                            try{

                                   while(true){

                                          //生产苹果

                                          System.out.println("生产者准备生产苹果: " + System.currentTimeMillis());

                                          basket.produce();

                                          System.out.println("生产者生产苹果完毕: " + System.currentTimeMillis());

                                          //休眠300ms

                                          Thread.sleep(300);

                                   }

                            }catch(InterruptedException ex){

                            }

                     }

              }

              //定义苹果消费者

              class Consumer implements Runnable{

                     public void run(){

                            try{

                                   while(true){

                                          //消费苹果

                                          System.out.println("消费者准备消费苹果: " + System.currentTimeMillis());

                                          basket.consume();

                                          System.out.println("消费者消费苹果完毕: " + System.currentTimeMillis());

                                          //休眠1000ms

                                          Thread.sleep(1000);

                                   }

                            }catch(InterruptedException ex){

                            }

                     }

              }

              ExecutorService service = Executors.newCachedThreadPool();

              Producer producer = new Producer();

              Consumer consumer = new Consumer();

              service.submit(producer);

              service.submit(consumer);

              //程序运行5s后,所有任务停止

              try{

                     Thread.sleep(5000);

              }catch(InterruptedException ex){

              }

              service.shutdownNow();

       }

       public static void main(String[] args){

              BlockingQueueTest.testBasket();

       }

}