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 [J2SE]Java Concurrent框架之阻塞队列（Blocking queue）
软件技术
lhwork 发表于 2006/9/15 10:04:37 |
| 引子：大家上过操作系统的都知道“生产者－消费者（Producer-Consumer）”模型，主要讨论的是进程（线程）间的互斥和同步问题，关键是对锁（lock）的申请、独占和释放，在这里我就不罗嗦了。原先我写的Java代码如下：
500)this.width=500'>500)this.width=500'>public class Producer extends Thread500)this.width=500'>{500)this.width=500'> private ProductList products = ProductList.getInstance();500)this.width=500'> 500)this.width=500'>500)this.width=500'> public void run()500)this.width=500'>{500)this.width=500'> int i = 0;500)this.width=500'> 500)this.width=500'>500)this.width=500'> while(i <= 20)500)this.width=500'>{500)this.width=500'>500)this.width=500'> synchronized(products)500)this.width=500'>{ // Get lock on product list500)this.width=500'>500)this.width=500'> if(products.isFull())500)this.width=500'>{500)this.width=500'> System.out.println("List is full");500)this.width=500'> products.notify(); // Release the lock500)this.width=500'>500)this.width=500'> } else500)this.width=500'>{500)this.width=500'> Product product = new Product(i++); // Produce a product500)this.width=500'> products.put(product);500)this.width=500'> System.out.println("Produced product " + product.getId());500)this.width=500'> products.notify(); // Release lock500)this.width=500'> }500)this.width=500'> } // Release the lock500)this.width=500'> }500)this.width=500'> }500)this.width=500'>}
500)this.width=500'>500)this.width=500'>public class Consumer extends Thread500)this.width=500'>{500)this.width=500'> ProductList products = ProductList.getInstance();500)this.width=500'> 500)this.width=500'>500)this.width=500'> public void run()500)this.width=500'>{500)this.width=500'>500)this.width=500'> while(true)500)this.width=500'>{500)this.width=500'>500)this.width=500'> synchronized(products)500)this.width=500'>{500)this.width=500'>500)this.width=500'> try 500)this.width=500'>{500)this.width=500'> products.wait(); // Wait for lock500)this.width=500'> Product product = null;500)this.width=500'> if(!(products.isEmpty()))500)this.width=500'> product = products.take();500)this.width=500'> else500)this.width=500'> System.out.println("List is empty");500)this.width=500'> System.out.println("Consumed product " + product.getId()); // Get the lock500)this.width=500'>500)this.width=500'> } catch (InterruptedException ex) 500)this.width=500'>{500)this.width=500'> ex.printStackTrace();500)this.width=500'> }500)this.width=500'> } // Release the lock500)this.width=500'> }500)this.width=500'> }500)this.width=500'>}500)this.width=500'>
500)this.width=500'>import java.util.ArrayList;500)this.width=500'>import java.util.List;500)this.width=500'>500)this.width=500'>500)this.width=500'>public class ProductList 500)this.width=500'>{500)this.width=500'> private static ProductList instance = new ProductList();500)this.width=500'> private List<Product> products; // Adapter pattern500)this.width=500'> public static final int SIZE = 10;500)this.width=500'> 500)this.width=500'>500)this.width=500'> private ProductList() 500)this.width=500'>{500)this.width=500'> products = new ArrayList<Product>(SIZE);500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public static ProductList getInstance() 500)this.width=500'>{ // Singleton pattern500)this.width=500'> return instance;500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public boolean isFull() 500)this.width=500'>{500)this.width=500'> return products.size() == SIZE;500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public void put(Product product) 500)this.width=500'>{500)this.width=500'> products.add(product);500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public Product take() 500)this.width=500'>{500)this.width=500'> return products.remove(0);500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public boolean isEmpty() 500)this.width=500'>{500)this.width=500'> return products.isEmpty();500)this.width=500'> }500)this.width=500'>}500)this.width=500'>
500)this.width=500'>500)this.width=500'>public class Product 500)this.width=500'>{500)this.width=500'> private int id;500)this.width=500'> 500)this.width=500'>500)this.width=500'> public Product(int id) 500)this.width=500'>{500)this.width=500'> this.id = id;500)this.width=500'> }500)this.width=500'> 500)this.width=500'>500)this.width=500'> public int getId() 500)this.width=500'>{500)this.width=500'> return id;500)this.width=500'> }500)this.width=500'>}500)this.width=500'>
500)this.width=500'>500)this.width=500'>public class Main 500)this.width=500'>{500)this.width=500'>500)this.width=500'> public static void main(String[] args)500)this.width=500'>{500)this.width=500'> Producer p = new Producer();500)this.width=500'> Consumer c = new Consumer();500)this.width=500'> 500)this.width=500'> p.start();500)this.width=500'> c.start();500)this.width=500'> }500)this.width=500'>}500)this.width=500'>虽
然Java对信号量及原语做了更高层次的封装（wait()、notify()、notifyAll()、synchronized{}），但看完上述代
码还是觉得有点麻烦，于是JDK
5在原先collection框架的基础上增加了java.util.concurrent包，封装了许多用于线程并发操作的数据结构和操作。其中的
BlockingQueue接口就是封装了一个阻塞队列的接口，具体地说就是实现了一个用于消费者（多个）和生产者（多个）交换产品的中介，生产者线程在
队列满时阻塞，消费者线程在队列空时阻塞，当然在没有得到锁之前两类线程均会阻塞。详细信息可以参考Java
Doc。下面用BlockingQueue实现P-C模型：
500)this.width=500'>500)this.width=500'>class Producer implements Runnable 500)this.width=500'>{500)this.width=500'> private final BlockingQueue queue;500)this.width=500'>500)this.width=500'> Producer(BlockingQueue q) 500)this.width=500'>{ queue = q; }500)this.width=500'>500)this.width=500'> public void run() 500)this.width=500'>{500)this.width=500'>500)this.width=500'> try 500)this.width=500'>{500)this.width=500'>500)this.width=500'> while(true) 500)this.width=500'>{ queue.put(produce()); }500)this.width=500'>500)this.width=500'> } catch (InterruptedException ex) 500)this.width=500'>{ 500)this.width=500'> handle 500)this.width=500'>}500)this.width=500'> }500)this.width=500'>500)this.width=500'> Object produce() 500)this.width=500'>{ 500)this.width=500'> }500)this.width=500'> }500)this.width=500'>500)this.width=500'>500)this.width=500'> class Consumer implements Runnable 500)this.width=500'>{500)this.width=500'> private final BlockingQueue queue;500)this.width=500'>500)this.width=500'> Consumer(BlockingQueue q) 500)this.width=500'>{ queue = q; }500)this.width=500'>500)this.width=500'> public void run() 500)this.width=500'>{500)this.width=500'>500)this.width=500'> try 500)this.width=500'>{500)this.width=500'>500)this.width=500'> while(true) 500)this.width=500'>{ consume(queue.take()); }500)this.width=500'>500)this.width=500'> } catch (InterruptedException ex) 500)this.width=500'>{ 500)this.width=500'> handle 500)this.width=500'>}500)this.width=500'> }500)this.width=500'>500)this.width=500'> void consume(Object x) 500)this.width=500'>{ 500)this.width=500'> }500)this.width=500'> }500)this.width=500'>500)this.width=500'>500)this.width=500'> class Setup 500)this.width=500'>{500)this.width=500'>500)this.width=500'> void main() 500)this.width=500'>{500)this.width=500'> BlockingQueue q = new SomeQueueImplementation();500)this.width=500'> Producer p = new Producer(q);500)this.width=500'> Consumer c1 = new Consumer(q);500)this.width=500'> Consumer c2 = new Consumer(q);500)this.width=500'> new Thread(p).start();500)this.width=500'> new Thread(c1).start();500)this.width=500'> new Thread(c2).start();500)this.width=500'> }500)this.width=500'> }500)this.width=500'>可以看出代码中没有出现wait()或notify()之类的原语操作，这些操作由concurrent框架负责封装。更全面的讨论可以参考《驯服 Tiger: 并发集合》（IBM） |
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