用Java实现生产者消费者的几种方法

一、采用synchronized锁以及wait notify方法实现
import java.io.IOException;

public class WaitAndNotify
{
	public static void main(String[] args) throws IOException
	{
		Person person = new Person();
		new Thread(new Consumer("消费者一", person)).start();
		new Thread(new Consumer("消费者二", person)).start();
		new Thread(new Consumer("消费者三", person)).start();

		new Thread(new Producer("生产者一", person)).start();
		new Thread(new Producer("生产者一", person)).start();
		new Thread(new Producer("生产者一", person)).start();

	}
}

class Producer implements Runnable
{
	private Person person;
	private String producerName;

	public Producer(String producerName, Person person)
	{
		this.producerName = producerName;
		this.person = person;
	}

	@Override
	public void run()
	{
		while (true)
		{
			try
			{
				person.produce();
			} catch (InterruptedException e)
			{
				e.printStackTrace();
			}
		}
	}

}

class Consumer implements Runnable
{

	private Person person;
	private String consumerName;

	public Consumer(String consumerName, Person person)
	{
		this.consumerName = consumerName;
		this.person = person;
	}

	@Override
	public void run()
	{
		try
		{
			person.consume();
		} catch (InterruptedException e)
		{
			e.printStackTrace();
		}

	}

}

class Person
{
	private int foodNum = 0;
	private Object synObj = new Object();

	private final int MAX_NUM = 5;

	public void produce() throws InterruptedException
	{
		synchronized (synObj)
		{
			while (foodNum == 5)
			{
				System.out.println("box is full,size = " + foodNum);
				synObj.wait();
			}
			foodNum++;
			System.out.println("produce success foodNum = " + foodNum);
			synObj.notifyAll();
		}

	}

	public void consume() throws InterruptedException
	{
		synchronized (synObj)
		{
			while (foodNum == 0)
			{
				System.out.println("box is empty,size = " + foodNum);
				synObj.wait();
			}
			foodNum--;
			System.out.println("consume success foodNum = " + foodNum);
			synObj.notifyAll();
		}

	}
}

二、采用Lock锁以及await和signal方法是实现

import java.io.IOException;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;

/**
 * @author 作者 E-mail:
 * @version 创建时间:2015-10-23 下午04:08:39 类说明
 */
public class AwaitAndSignal
{
    public static void main(String[] args) throws IOException
    {
        Person person = new Person();
        new Thread(new Consumer(person), "消费者一").start();
        new Thread(new Consumer(person), "消费者二").start();
        new Thread(new Consumer(person), "消费者三").start();

        new Thread(new Producer(person), "生产者一").start();
        new Thread(new Producer(person), "生产者一").start();
        new Thread(new Producer(person), "生产者一").start();
    }
}

class Producer implements Runnable
{
    private Person person;

    public Producer(Person person)
    {
        this.person = person;
    }

    @Override
    public void run()
    {

        for (int i = 0; i < 10; i++)
        {
            person.produce();
        }

    }

}

class Consumer implements Runnable
{

    private Person person;

    public Consumer(Person person)
    {
        this.person = person;
    }

    @Override
    public void run()
    {

        for (int i = 0; i < 10; i++)
        {
            person.consume();
        }

    }

}

class Person
{
    private int foodNum = 0;

    private ReentrantLock lock = new ReentrantLock();

    private Condition condition = lock.newCondition();

    private final int MAX_NUM = 5;

    public void produce()
    {
        lock.lock();
        try
        {
            while (foodNum == MAX_NUM)
            {
                System.out.println("box is full,size = " + foodNum);
                condition.await();
            }
            foodNum++;
            System.out.println("produce success foodNum = " + foodNum);
            condition.signalAll();
        }
        catch(InterruptedException e)
        {
            e.printStackTrace();
        } finally
        {
            lock.unlock();
        }

    }

    public void consume()
    {
        lock.lock();
        try
        {
            while (foodNum == 0)
            {
                System.out.println("box is empty,size = " + foodNum);
                condition.await();
            }
            foodNum--;
            System.out.println("consume success foodNum = " + foodNum);
            condition.signalAll();
        }
        catch(InterruptedException e)
        {
            e.printStackTrace();
        } finally
        {
            lock.unlock();
        }

    }
}

三、采用BlockingQueue实现

BlockingQueue也是java.util.concurrent下的主要用来控制线程同步的工具。

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:一个由数组支持的有界阻塞队列,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。


LinkedBlockingQueue 可以指定容量,也可以不指定,不指定的话,默认最大是Integer.MAX_VALUE,其中主要用到put和take方法,put方法在队列满的时候会阻塞直到有队列成员被消费,take方法在队列空的时候会阻塞,直到有队列成员被放进来。

import java.util.concurrent.BlockingQueue;  
  
public class Producer implements Runnable {  
    BlockingQueue<String> queue;  
  
    public Producer(BlockingQueue<String> queue) {  
        this.queue = queue;  
    }  
  
    @Override  
    public void run() {  
        try {  
            String temp = "A Product, 生产线程:"  
                    + Thread.currentThread().getName();  
            System.out.println("I have made a product:"  
                    + Thread.currentThread().getName());  
            queue.put(temp);//如果队列是满的话,会阻塞当前线程  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
    }  
  
}  

import java.util.concurrent.BlockingQueue;  
  
public class Consumer implements Runnable{  
    BlockingQueue<String> queue;  
      
    public Consumer(BlockingQueue<String> queue){  
        this.queue = queue;  
    }  
      
    @Override  
    public void run() {  
        try {  
            String temp = queue.take();//如果队列为空,会阻塞当前线程  
            System.out.println(temp);  
        } catch (InterruptedException e) {  
            e.printStackTrace();  
        }  
    }  
}  

import java.util.concurrent.ArrayBlockingQueue;  
import java.util.concurrent.BlockingQueue;  
import java.util.concurrent.LinkedBlockingQueue;  
  
public class Test3 {  
  
    public static void main(String[] args) {  
      BlockingQueue<String> queue = new LinkedBlockingQueue<String>(2);  
     // BlockingQueue<String> queue = new LinkedBlockingQueue<String>();  
     //不设置的话,LinkedBlockingQueue默认大小为Integer.MAX_VALUE  
          
    // BlockingQueue<String> queue = new ArrayBlockingQueue<String>(2);  
  
        Consumer consumer = new Consumer(queue);  
        Producer producer = new Producer(queue);  
        for (int i = 0; i < 5; i++) {  
            new Thread(producer, "Producer" + (i + 1)).start();  
  
            new Thread(consumer, "Consumer" + (i + 1)).start();  
        }  
    }  
}  
BlockingQueue接口,扩展了Queue接口
package java.util.concurrent;

import java.util.Collection;
import java.util.Queue;

public interface BlockingQueue<E> extends Queue<E> {
    boolean add(E e);

    boolean offer(E e);

    void put(E e) throws InterruptedException;

    boolean offer(E e, long timeout, TimeUnit unit)
        throws InterruptedException;
    E take() throws InterruptedException;

    E poll(long timeout, TimeUnit unit)
        throws InterruptedException;

    int remainingCapacity();

    boolean remove(Object o);

    public boolean contains(Object o);

    int drainTo(Collection<? super E> c);

    int drainTo(Collection<? super E> c, int maxElements);
}

我们用到的take() 和put(E e)

两个方法,在ArrayBlockingQueue中的实现

  public void put(E e) throws InterruptedException {
        if (e == null) throw new NullPointerException();
        final E[] items = this.items;
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            try {
                while (count == items.length)
                    notFull.await();
            } catch (InterruptedException ie) {
                notFull.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            insert(e);
        } finally {
            lock.unlock();
        }
  }

 private void insert(E x) {
        items[putIndex] = x;
        putIndex = inc(putIndex);
        ++count;
        notEmpty.signal();
}

 public E take() throws InterruptedException {
        final ReentrantLock lock = this.lock;
        lock.lockInterruptibly();
        try {
            try {
                while (count == 0)
                    notEmpty.await();
            } catch (InterruptedException ie) {
                notEmpty.signal(); // propagate to non-interrupted thread
                throw ie;
            }
            E x = extract();
            return x;
        } finally {
            lock.unlock();
        }
    }
 private E extract() {
        final E[] items = this.items;
        E x = items[takeIndex];
        items[takeIndex] = null;
        takeIndex = inc(takeIndex);
        --count;
        notFull.signal();
        return x;
    }

看得到其实也是利用了Lock以及Condition条件变量的await()方法和signal()方法实现的,这个实现和我们之前实现的Lock用法区别:

1)使用了两个条件变量 consume的await放置在notEmpty 之上,唤醒在put的时候,produce的await放置在notfull之上,唤醒在take()的时候,唤醒是signal而不是signalAll,这样做就不会因为大量唤醒导致竞争从而减低效率,通过锁对象的分析,减低竞争

优点:更有利于协调生产消费线程的平衡

编辑于 2016-08-20

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