if ( 0 != Thread.VolatileRead(queue.Count) ) {
    lock(queue) {
        if ( 0 != Thread.VolatileRead(queue.Count) )
            var msq = queue.Dequeue();
    }
}

class Program
    {
        static readonly Queue<string> _queue = new Queue<string>();

        static void Main(string[] args)
        {
            (new Thread(() =>
                {
                    while (true)
                    {
                        if (0 < _queue.Count)
                        {
                            lock (_queue)
                            {
                                while (0 != _queue.Count)
                                {
                                    string msg = _queue.Dequeue();
                                    Console.WriteLine(msg);
                                }
                            }
                        }                        
                    }

                }) {IsBackground = true}).Start();
            Thread.Sleep(1000);

            Enumerable.Range(1, 25).ToList().ForEach(i => (new Thread(Handler) {IsBackground = true}).Start(i));

            Console.ReadKey();
        }

        static void Handler(object state)
        {
            while (true)
            {
                lock (_queue)
                    _queue.Enqueue(((int)state).ToString());
                Thread.Sleep(1);
            }
            
        }
    }