java - 生产者线程之后的最终消费者线程并消耗所有元素

Question

我已经编写了使用等待和通知来实现生产者消费者问题的代码。它工作正常但问题是消费者线程在无限循环中运行并且即使在生产者线程完成并且消费者已经消耗了列表中的所有元素之后仍在等待。

public class Practice {

    public static void main(String[] args) {

        List<Employee> empList = new ArrayList<Employee>();
        Thread producer = new Thread(new Producer(empList , 2) , "Producer");
        Thread consumer = new Thread(new Consumer(empList , 2) , "Consumer");

        producer.start();
        consumer.start();
    }

}

class Employee 
{
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}
class Producer implements Runnable 
{
    List<Employee> empList; 
    int size;

    public Producer(final List<Employee> empList  , final int size)
    {
        this.empList = empList;
        this.size = size;
    }

    @Override    
    public void run()
    {
        for(int i=0; i<5;i++)
        {
            try {
                produce(new Employee());
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void produce(Employee e) throws InterruptedException
    {
        synchronized(empList){
            while(empList.size()==size) // If list is full then will have to wait
            {

                System.out.println("List is full "+Thread.currentThread().getName()+" Is waiting and" + " Size is "+empList.size());
                empList.wait();
            }
        }

        synchronized(empList)
        {
            System.out.println("Producing");
            empList.add(e);
            empList.notifyAll();
        }
    }
}


class Consumer implements Runnable 
{
    List<Employee> empList; 
    int size;

    public Consumer(final List<Employee> empList  , final int size)
    {
        this.empList = empList;
        this.size = size;
    }

    @Override    
    public void run()
    {
        while(true)
        {
            try {
                System.out.println("Consumed ");
                consume();
                Thread.sleep(50);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void consume() throws InterruptedException
    {
        synchronized(empList){
            while(empList.isEmpty()) // If list is empty then will have to wait
            {
                System.out.println("List is empty "+Thread.currentThread().getName()+" Is waiting and " + "Size is "+empList.size());
                empList.wait();
            }
        }

        synchronized(empList)
        {
            empList.notifyAll();
            empList.remove(0);
        }

    }    

}

请告诉我如何在生产者完成并且消费者已经消耗了列表中的所有元素后停止我的消费者线程。请帮助我的代码。提前致谢

Answer 1

只需添加标志，在生产者和消费者之间共享:

static bool producerFinished = false;

在它生产完所有元素后在生产者中设置它:

public void run()
{
    // ...
    synchronized(empList){
        producerFinished = true;
        empList.notifyAll();
    }
}

并在消费者的 while() 循环中检查它以及列表是否为空

public void consume()
{
    synchronized(empList){
        while(empList.isEmpty() && !producerFinished)
        {
            empList.wait();
        }

        if(!empList.isEmpty())
        {
            //consume element
        }
        else
        {
            //List is empty and producer has finished.
        }
    }
}