C# producer/consumer

Question

i've recently come across a producer/consumer pattern c# implementation. it's very simple and (for me at least) very elegant.

it seems to have been devised around 2006, so i was wondering if this implementation is
- safe
- still applicable

Code is below (original code was referenced at http://bytes.com/topic/net/answers/575276-producer-consumer#post2251375)

using System;  
using System.Collections;  
using System.Threading;

public class Test
{  
    static ProducerConsumer queue;

    static void Main()
    {
        queue = new ProducerConsumer();
        new Thread(new ThreadStart(ConsumerJob)).Start();

        Random rng = new Random(0);
        for (int i=0; i < 10; i++)
        {
            Console.WriteLine ("Producing {0}", i);
            queue.Produce(i);
            Thread.Sleep(rng.Next(1000));
        }
    }

    static void ConsumerJob()
    {
        // Make sure we get a different random seed from the
        // first thread
        Random rng = new Random(1);
        // We happen to know we've only got 10 
        // items to receive
        for (int i=0; i < 10; i++)
        {
            object o = queue.Consume();
            Console.WriteLine ("\t\t\t\tConsuming {0}", o);
            Thread.Sleep(rng.Next(1000));
        }
    }
}

public class ProducerConsumer
{
    readonly object listLock = new object();
    Queue queue = new Queue();

    public void Produce(object o)
    {
        lock (listLock)
        {
            queue.Enqueue(o);

            // We always need to pulse, even if the queue wasn't
            // empty before. Otherwise, if we add several items
            // in quick succession, we may only pulse once, waking
            // a single thread up, even if there are multiple threads
            // waiting for items.            
            Monitor.Pulse(listLock);
        }
    }

    public object Consume()
    {
        lock (listLock)
        {
            // If the queue is empty, wait for an item to be added
            // Note that this is a while loop, as we may be pulsed
            // but not wake up before another thread has come in and
            // consumed the newly added object. In that case, we'll
            // have to wait for another pulse.
            while (queue.Count==0)
            {
                // This releases listLock, only reacquiring it
                // after being woken up by a call to Pulse
                Monitor.Wait(listLock);
            }
            return queue.Dequeue();
        }
    }
}

Answer 1

The code is older than that - I wrote it some time before .NET 2.0 came out. The concept of a producer/consumer queue is way older than that though :)

Yes, that code is safe as far as I'm aware - but it has some deficiencies:

• It's non-generic. A modern version would certainly be generic.
• It has no way of stopping the queue. One simple way of stopping the queue (so that all the consumer threads retire) is to have a "stop work" token which can be put into the queue. You then add as many tokens as you have threads. Alternatively, you have a separate flag to indicate that you want to stop. (This allows the other threads to stop before finishing all the current work in the queue.)
• If the jobs are very small, consuming a single job at a time may not be the most efficient thing to do.

The ideas behind the code are more important than the code itself, to be honest.