1.cs

using System.Threading;

Random rand = new Random();

const int BUFFER_SIZE = 5;
int[] m_buffer = new int[BUFFER_SIZE];
int m_count = 0;


void Produce()
{
    while (true)
    {
        lock (m_buffer)
        {
            int value = rand.Next(0, 100);

            if (m_count == BUFFER_SIZE)
            {
                Console.WriteLine("[{0}] Skipped: {1}", m_count, value);
            }
            else
            {
                m_buffer[m_count] = value;
                ++m_count;
                Console.WriteLine("[{0}] Produced.", m_count);
            }
        }
    }
}

void Consume()
{
    while (true)
    {
        lock (m_buffer)
        {
            int value = -1;

            if (m_count > 0)
            {
                value = m_buffer[m_count - 1];
                --m_count;
            }

            Console.WriteLine("[{0}] Consuming: {1}", m_count, value);
        }
    }
}

void Main()
{
    for (int i = 0; i < 4; ++i)
    {
        Thread producer = new Thread(new ThreadStart(Produce));
        Thread consumer = new Thread(new ThreadStart(Consume));
        producer.Start();
        consumer.Start();
    }
    
    Console.ReadKey();
}

Main();