public partial class Form1 : Form
    {

        public delegate void SafeRefresh();
        public SafeRefresh myDelegate;
        private Form1 currentForm;
        Thread scriptThread;

        public Form1()
        {
            InitializeComponent();
            currentForm = this;
            myDelegate = new SafeRefresh(SafeRefreshAllMethod);

        }
        private async void button_script_Click(object sender, EventArgs e)
        {
            scriptThread = new Thread( () => SomeClass.RunScript(currentForm));
            scriptThread.Start();
        }

        public void SafeRefreshAllMethod()
        {

            listBox.DataSource = null;
            listBox.Refresh();
            listBox.DataSource = Global.ListAllItems;
            listBox.Refresh();
        }


        public void listBox_DrawItem(object sender, DrawItemEventArgs e)
        {
            Brush myBrush;
            if (Global.ListItemsDisconnected.Contains(Global.ListAllItems[e.Index] ))
            {
                myBrush = Brushes.Gray;
            }
            else if (Global.ListItemsConnected.Contains(Global.ListAllItems[e.Index]))
            {
                myBrush = Brushes.Green;
            }
            else
            {
                myBrush = Brushes.Black;
            }

            e.DrawBackground();
            e.Graphics.DrawString(listBox.Items[e.Index].ToString(), listBox.Font, myBrush, e.Bounds);
        }

    }

class SomeClass {
public static void  RunScript(Form1 theForm)
        {

            foreach (string item in Global.ListAllItems)
            {

                //some code that works with the items on list
                //if disconnected : adds to Global.ListItemsDisconnected
                //if connected: adds it to Global.ListItemsConnected

                theForm.Invoke(theForm.myDelegate);


            }
        }
}