Why this consumer-producer thread is frozen?

Question

I've made this producer-consumer sample, but I don't know why it freezes at the end. Where is the problem? If I put a breakpoint at line setNum(-99); and then after break continue it finishes OK. Please also tell me if this code is ok and threadsafe. It must work like that, so meanwhile consumer is processing its given value, all other values from producer must be ignored. I am very new to multithreading.

class Program
{
    delegate void SetNumberDelegate(int number);
    static void Main(string[] args)
    {
        Random rnd = new Random();
        ConsumerClass consumerClass = new ConsumerClass();
        SetNumberDelegate setNum = new SetNumberDelegate(consumerClass.setNumber);
        Thread.Sleep(20);
        int num;
        int count = 0;
        Console.WriteLine("Start");
        while (count++ < 100)
        {
            num = rnd.Next(0, 100);
            Console.WriteLine("Generated number {0}", num);
            if (num > 30)
            {
                setNum(num);
            }
        }
        setNum(-99);
        Console.WriteLine("End");
        Console.ReadKey();
    }
}

class ConsumerClass : IDisposable
{
    private int number;
    private object locker = new object();
    private EventWaitHandle _wh = new AutoResetEvent(false);
    private Thread _consumerThread;

    public ConsumerClass()
    {
        number = -1;
        _consumerThread = new Thread(consumeNumbers);
        _consumerThread.Start();
    }

    public void Dispose()
    {
        setNumber(-99);
        _consumerThread.Join();         
        _wh.Close();
    }

    public void setNumber(int num)
    {
        if (Monitor.TryEnter(locker))
        {
            try
            {
                number = num;
                Console.WriteLine("Setting number {0}", number);
            }
            finally
            {
                // Ensure that the lock is released.
                Monitor.Exit(locker);
            }
            _wh.Set();
        }
    }

    public void consumeNumbers()
    {
        while (true)
        {
            Monitor.Enter(locker);
            if (number > -1)
            {
                try
                {
                    Console.WriteLine("Processing number:{0}", number);
                    // simulate some work with number e.g. computing and storing to db
                    Thread.Sleep(20);
                    Console.WriteLine("Done");
                    number = -1;
                }
                finally
                {
                    Monitor.Exit(locker);
                }
            }
            else
            {
                if (number == -99)
                {
                    Console.WriteLine("Consumer thread exit");
                    return;
                }
                Monitor.Exit(locker);
                _wh.WaitOne();         // No more tasks - wait for a signal
            }
        }
    }
}

Answer 1

Rewrite setNumber like this to see your problem:

public void setNumber(int num) {
    if (Monitor.TryEnter(locker)) {
        // etc..
    }
    else Console.WriteLine("Number {0} will never make it to the consumer", num);
}

You'll have to block, waiting for the consumer to be ready to consume or use a queue.