C#生产者/消费者模式

Question

我有简单的一个生产者/两个消费者代码如下,但输出显示只有C2消耗.我的代码中有任何错误吗？

class Program
{
    static void Main(string[] args)
    {
        Object lockObj = new object();
        Queue<string>  queue = new Queue<string>();
        Producer p = new Producer(queue, lockObj);
        Consumer c1 = new Consumer(queue, lockObj, "c1");
        Consumer c2 = new Consumer(queue, lockObj, "c2");

        Thread t1 = new Thread(c1.consume);
        Thread t2 = new Thread(c2.consume);
        t1.Start();
        t2.Start();

        Thread t = new Thread(p.produce);
        t.Start();

        Console.ReadLine();
    } 
}
public class Producer
{
    Queue<string> queue;
    Object lockObject;
    static int seq = 0;
    public Producer(Queue<string> queue, Object lockObject)
    {
        this.queue = queue;
        this.lockObject = lockObject; 
    }

    public void produce()
    {
        while( seq++ <15) //just testinng 15 items
        {
            lock (lockObject)
            {
                string item = "item" + seq;
                queue.Enqueue(item);
                Console.WriteLine("Producing {0}", item);
                if (queue.Count == 1)
                { // first
                    Monitor.PulseAll(lockObject);
                }
            }
        }
    }

}

public class Consumer
{
    Queue<string> queue;
    Object lockObject;
    string name;
    public Consumer(Queue<string> queue, Object lockObject, string name)
    {
        this.queue = queue;
        this.lockObject = lockObject; 
        this.name = name;
    }

    public void consume()
    {
        string item;
        while (true)
        {
            lock (lockObject)
            {
                if (queue.Count == 0)
                { 
                    Monitor.Wait(lockObject);
                    continue; 
                }
                item = queue.Dequeue();
                Console.WriteLine(" {0} Consuming {1}", name, item);
            }
        }
    }
}

输出是:

Producing item1
 c2 Consuming item1

Producing item2
 c2 Consuming item2

Producing item3
 c2 Consuming item3

Producing item4
 c2 Consuming item4

Producing item5
 c2 Consuming item5

Producing item6
 c2 Consuming item6

Producing item7
 c2 Consuming item7

Producing item8
 c2 Consuming item8

Producing item9
 c2 Consuming item9

Producing item10
 c2 Consuming item10

Producing item11
 c2 Consuming item11

Producing item12
 c2 Consuming item12

Producing item13
 c2 Consuming item13

Producing item14
 c2 Consuming item14

Producing item15
 c2 Consuming item15

Answer 1

首先,我无法重现您的问题,这里两个线程都消耗了一些项目.我想你的机器速度更快,但像gw建议的那样添加睡眠会解决这个问题.我还建议你不要尝试同步生产者,我的意思是让它尽可能快地排队项目,让消费者同步看看谁处理每个项目.我做了一个快速修改,似乎工作正常:

static void Main()
    {
        Object lockObj = new object();
        Queue<string> queue = new Queue<string>();
        Producer p = new Producer(queue);
        Comsumer c1 = new Comsumer(queue, lockObj, "c1");
        Comsumer c2 = new Comsumer(queue, lockObj, "c2");

        Thread t1 = new Thread(c1.consume);
        Thread t2 = new Thread(c2.consume);
        t1.Start();
        t2.Start();

        Thread t = new Thread(p.produce);
        t.Start();

        Console.ReadLine();
    }
}
public class Producer
{
    Queue<string> queue;
    static int seq;
    public Producer(Queue<string> queue)
    {
        this.queue = queue;
    }

    public void produce()
    {
        while (seq++ < 1000) //just testinng 15 items
        {
            string item = "item" + seq;
            queue.Enqueue(item);
            Console.WriteLine("Producing {0}", item);                
        }
    }
}

public class Comsumer
{
    Queue<string> queue;
    Object lockObject;
    string name;
    public Comsumer(Queue<string> queue, Object lockObject, string name)
    {
        this.queue = queue;
        this.lockObject = lockObject;
        this.name = name;
    }

    public void consume()
    {
        string item;
        while (true)
        {
            lock (lockObject)
            {
                if (queue.Count == 0)
                {
                    continue;
                }
                item = queue.Dequeue();
                Console.WriteLine(" {0} Comsuming {1}", name, item);
            }                
        }
    }
}

您还可以添加睡眠以减慢消费者循环.

Answer 2

出于测试目的，请尝试在消费者代码中添加时间延迟。可能出现的情况是“消费”太快，以至于一个消费者线程在另一个消费者线程有机会之前清空了队列。

（编辑）

正如我怀疑的那样，添加一个

线程.睡眠(500);

在消费者线程内部（以模拟正在进行的一些冗长处理）导致两个线程都被利用。