Java核心知识点学习----多线程中的阻塞队列,ArrayBlockingQueue介绍

1.什么是阻塞队列?

所谓队列,遵循的是先进先出原则(FIFO),阻塞队列,即是数据共享时,A在写数据时,B想读同一数据,那么就将发生阻塞了.

看一下线程的四种状态,首先是新创建一个线程,然后,通过start方法启动线程--->线程变为可运行可执行状态,然后通过数据产生共享,线程产生互斥---->线程状态变为阻塞状态---->阻塞状态想打开的话可以调用notify方法.

这里Java5中提供了封装好的类,可以直接调用然后构造阻塞状态,以保证数据的原子性.

2.如何实现?

主要是实现BlockingQueue接口.

比较常见的实现有:ArrayBlockingQueue,LinkedBlockingQueue,DelayedWorkQueue等竺

这里简单介绍ArrayBlockingQueue;

//方式1
new ArrayBlockingQueue(int capacity);//Parameters:capacity the capacity of this queue

//方式2
public ArrayBlockingQueue(int capacity, boolean fair) ;//fair if true then queue accesses for threads blocked on insertion or removal, are processed in 
     FIFO order; if false the access order is unspecified.

//方式3
 public ArrayBlockingQueue(int capacity, boolean fair,
                              Collectionextends E> c) ;//c the collection of elements to initially contain

    

三种构造函数,比较常用的是1,2两种,2比1只是多了要不要排序,如果排序,那就是FIFO原则,即先进先出.

3.举例:

package com.amos.concurrent;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

/** 
* @ClassName: BlockingQueueTest 
* @Description: Java5新特性,阻塞队列
* @author: amosli
* @email:[email protected]
* @date Apr 27, 2014 10:01:51 PM  
*/
public class BlockingQueueTest {
    public static void main(String[] args) {
        final BlockingQueue queue = new ArrayBlockingQueue(3);
        for(int i=0;i<2;i++){
            new Thread(){
                public void run(){
                    while(true){
                        try {
                            Thread.sleep((long)(Math.random()*1000));
                            System.out.println(Thread.currentThread().getName() + "准备放数据!");                            
                            queue.put(1);
                            System.out.println(Thread.currentThread().getName() + "已经放了数据，" +                             
                                        "队列目前有" + queue.size() + "个数据");
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }

                    }
                }
                
            }.start();
        }
        
        new Thread(){
            public void run(){
                while(true){
                    try {
                        //将此处的睡眠时间分别改为100和1000，观察运行结果
                        Thread.sleep(100);
                        System.out.println(Thread.currentThread().getName() + "准备取数据!");
                        queue.take();
                        System.out.println(Thread.currentThread().getName() + "已经取走数据，" +                             
                                "队列目前有" + queue.size() + "个数据");                    
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
            
        }.start();            
    }
}

效果如下图所示:

说明:这里新建一个队列后,主要调用的是put和take两种方法,一个是存,一个是取,这里由于将取的间隔时间设置的比较短,所以基本队列就没放满过.

 

4.改写之前的代码

方法1:Java核心知识点学习----多线程并发之线程间的通信,notify,wait

方法2:Java核心知识点学习----使用Condition控制线程通信

方法3:使用ArrayBlockingQueue

package com.amos.concurrent;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;
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;

/** 
* @ClassName: BlockingQueueCondition 
* @Description: 在前面用Condition实现的同步通知的例子的基础上，改为用阻塞队列来实现。
第一个线程：A.take()……..B.put()
第二个线程：B.take()……..A.put()
* @author: amosli
* @email:[email protected]
* @date Apr 28, 2014 12:57:51 AM  
*/
public class BlockingQueueCondition {

    public static void main(String[] args) {
        ExecutorService service = Executors.newSingleThreadExecutor();
        final Business3 business = new Business3();
        service.execute(new Runnable(){

            public void run() {
                for(int i=0;i<2;i++){
                    business.sub();
                }
            }
            
        });
        
        for(int i=0;i<3;i++){
            business.main();
        }
    }

}

class Business3{
    BlockingQueue subQueue = new ArrayBlockingQueue(1);
    BlockingQueue mainQueue = new ArrayBlockingQueue(1);
    {
        try {
            mainQueue.put(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public void sub(){
        try
        {
            mainQueue.take();
            for(int i=0;i<10;i++){
                System.out.println(Thread.currentThread().getName() + " : " + i);
            }
            subQueue.put(1);
        }catch(Exception e){

        }
    }
    
    public void main(){
        
        try
        {
            subQueue.take();
            for(int i=0;i<5;i++){
                System.out.println(Thread.currentThread().getName() + " : " + i);
            }
            mainQueue.put(1);
        }catch(Exception e){
        }        
    }
}

功能的实现都是完全一样的,不同的是,使用ArrayBlockingQueue会更简单.

 

5.官方---代码示例

典型的生产者消费者模型:

package com.amos.concurrent;

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

/** 
* @ClassName: BlockingSample 
* @Description: 生产者消费者模型,阻塞,只有生产好了,才能去消费
* @author: amosli
* @email:[email protected]
* @date Apr 28, 2014 1:44:07 AM  
*/
public class BlockingSample {
    public static void main(String[] args) {
        new BlockingSample().new Setup().main();
    }
    class Producer implements Runnable {
           private final BlockingQueue queue;
           Producer(BlockingQueue q) { queue = q; }
           public void run() {
             try {
               while (true) { queue.put(produce());
               System.out.println(Thread.currentThread().getName()+" 现在正在生产!");
               }
             } catch (Exception ex) { ex.printStackTrace();}
           }
           String produce() { System.out.println("produce now ....");
            return "produce"; }
         }

         class Consumer implements Runnable {
           private final BlockingQueue queue;
           Consumer(BlockingQueue q) { queue = q; }
           public void run() {
             try {
               while (true) { consume(queue.take()); 
               System.out.println(Thread.currentThread().getName()+" 现在正在消费!");
               }
             } catch (InterruptedException ex) { ex.printStackTrace();}
           }
           void consume(Object x) {System.out.println("consume...");}
         }

         class Setup {
           void main() {
             BlockingQueue q = new ArrayBlockingQueue(1);
             Producer p = new Producer(q);
             Consumer c1 = new Consumer(q);
             Consumer c2 = new Consumer(q);
             new Thread(p).start();
             new Thread(c1).start();
             new Thread(c2).start();
           }
         }
         
}

效果如下图所示:

由图上可以看出,只有生产了才能消费,否则会形成阻塞.