C#

Random rand;

private void button1_Click(object sender, EventArgs e)
{
      rand=new Random();
      for (int i = 1; i <= 40; i++)
   {
      BackgroundWorker Computation = new BackgroundWorker();
      Computation.DoWork += new DoWorkEventHandler(Computation_DoWork);
      Computation.RunWorkerCompleted += new RunWorkerCompletedEventHandler(Computation_RunWorkerCompleted);
      Computation.RunWorkerAsync();
   }
}

private double timeOccurance2(string target)
{
   string trial = string.Empty;
   double intialTime = DateTime.Now.ToOADate();
   int targetLength = target.Length;

   while (trial != target)
   {
       StringBuilder b = new StringBuilder();
       char[] ch = new char[target.Length];
       for (int i = 0; i < target.Length; i++)
      {
         ch[i] = Convert.ToChar(Convert.ToInt32(Math.Floor(10 * rand.NextDouble() + 48)));
      }

      for (int i = 0; i < target.Length; i++)
      {
         b.Append(ch[i].ToString());
      }

      trial = b.ToString();
   }

   double finalTime = DateTime.Now.ToOADate();
   return 24 * 60 * 60 * (finalTime - intialTime);
}

private void Computation_DoWork(object sender, DoWorkEventArgs e)
{
   e.Result = timeOccurance2("124456").ToString();
}

private void Computation_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
   richTextBox1.Text += (string)(e.Result);
   richTextBox1.Text += (char)(10);
}

public partial class UserControl1 : UserControl
{
    public event EventHandler Button1Click;

    public UserControl1()
    {
        InitializeComponent();
        button1.Click += new EventHandler(button1_Click);
    }

    void button1_Click(object sender, EventArgs e)
    {
        OnButton1Click(e);
    }

    protected virtual void OnButton1Click(EventArgs e)
    {
        EventHandler eh = Button1Click;
        if (eh != null)
            eh(this, e);
    }
}

public class MyListOfObjects : List<MyObject>{}

public void AddUnique(MyObject obj)

int idx = oldList.BinarySearch(currentObject);
if(idx<0)//does not contain your code here ...

for(int i = GetLengthOfLongestList(); i>0; i--)
{
try
{
var currentNewObject=newList[i];
}
catch
{
//do some stuff here to avoid use later
}
and a 
try
{
var currentOldObject=oldList[i];
}
catch
{
//do some stuff here to avoid use later
}
/after checks
oldList.removeAt(i);
//or
oldList.add(currentNewObject);
}
}