public delegate void TestDeleg(string message);
    public class Data
    {
        public TestDeleg deleg;
        public string mess;
    }

    class test
    {

        public List<Thread> threads = new List<Thread>();
        public int nThreads = 0;
        public int maxThreads = 5;

        public void DoWork(object data)
        {
            Data d = (Data)data;
            d.deleg(d.mess);
            //string message = (string)data;
            //MessageBox.Show(d.mess);
            return;


        }

        public void CreateThread(object data)
        {
            if (nThreads >= maxThreads)
                return;
            Thread newThread = new Thread(DoWork);
            threads.Add(newThread);
            newThread.IsBackground = true;
            newThread.Start(data);
            nThreads++;


        }

        public void WindUpThreads()
        {
            //MessageBox.Show("count: " + nThreads.ToString());
            for(int i = 0; i < threads.Count; i++)
            {
                if (threads[i].IsAlive == false)
                {
                    threads[i].Abort();
                    threads.RemoveAt(i);
                   //MessageBox.Show("removing at " + i.ToString());
                }

            }

            nThreads = threads.Count;
        }

    }




private void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    test thTest = new test();
    string[] strings;
    try
    {

        strings = File.ReadAllLines("C:\\users\\alex\\desktop\\test.txt");
    }

    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
        return;
    }

    bool flag = true;
    int counter = 0;
    int dataCount = strings.Length;

    while (flag == true)
    {
        if (counter >= dataCount)
        {
            flag = false;
        }

        while (thTest.nThreads < thTest.maxThreads)
        {
            if (flag == false)
                break;

            //thTest.CreateThread(strings[counter]);
            Data d = new Data();
            d.deleg = AddItem;
            d.mess = strings[counter];
            thTest.CreateThread((object)d);
            //MessageBox.Show(counter.ToString());
            counter++;
        }

        thTest.WindUpThreads();

        if (flag == false)
        {
            do
            {
                thTest.WindUpThreads();

            } while (thTest.nThreads != 0);
        }



    }

    listBox1.Items.Add("Done");

}

public void AddItem(string message)
{

    lock(obj)
    {

        if(listBox1.InvokeRequired)
           Invoke( (Action)( () => { listBox1.Items.Add(message); } ) );
            //listBox1.BeginInvoke(new Action <string>(AddItem), message);
        else
            listBox1.Items.Add(message);
    }


}

}