static int a = 1;

static void Main(string[] argv)
{
    ThreadPool.QueueUserWorkItem(p =>
    {
        while (true)
        {
            Console.WriteLine(a);
            Thread.Sleep(500);
        }
    });

    Proc(out a);
}

private static void Proc(out int a)
{
    var ram = new Random();
    while (true)
    {
        Thread.Sleep(200);     
        a = ram.Next(1000);
    }
}