C#

public interface ITest
{
    TestResult PerformTest();
}

public class Test1 : ITest
{
    public TestResult PerformTest()
    {
        Thread.Sleep(60 * 10 * 1000);

        return TestResult.Failed;
    }
}

public class Test2 : ITest
{
    public TestResult PerformTest()
    {
        Thread.Sleep(60 * 2 * 1000);

        // Need to do some other stuff here. If Test1 is not finished, then wait for it to finish before continuing

        return TestResult.Passed;
    }
}

public enum TestResult
{
    Failed,

    Passed
}

class Program
{
    static List<Task> tasks = new List<Task>();

    static void Main(string[] args)
    {
        List<ITest> tests = new List<ITest>
        {
            new Test1(),
            new Test2()
        };

        foreach (var test in tests)
        {
            var task = Task.Factory.StartNew(() =>
            {
                TestResult testResult = test.PerformTest();
                return testResult;
            });

            tasks.Add(task);
        }

        try
        {
            Task.WaitAll(tasks.ToArray());
        }
        catch (Exception e)
        {
            throw e;
        }
    }
}

namespace threads
{
    class Program
    {

        public static int compteur;
        public static object ob = new object();
        public static SemaphoreSlim sem = new SemaphoreSlim(3);

        public static void Thread_test() {
            sem.Wait();
            for (int i = 0; i < 1000000; i++)
            {
                compteur++;
            }
            sem.Release();
            System.Console.WriteLine(compteur.ToString());
        }

        static void Main(string[] args)
        {
            Thread[] th = new Thread[10];
            for (int i = 0; i < th.Length; i++)
            {
                th[i] = new Thread(Thread_test)
                {
                    Name = "thread_" + i
                };
                th[i].Start();
            }

            System.Console.ReadLine();
        }
    }
}

thread_2 = 1264634
thread_0 = 1440996
thread_1 = 1645012
thread_3 = 2344585
thread_5 = 2694858
thread_4 = 2809001
thread_6 = 3628891
thread_8 = 3651918
thread_7 = 3991965
thread_9 = 4527904

thread_3 = 1893992
thread_1 = 2735536
thread_4 = 4274643
thread_2 = 4349873
thread_0 = 6248051
thread_5 = 7430503
thread_6 = 8107979
thread_7 = 8937401
thread_9 = 9815069
thread_8 = 10000000

<ComboBox  x:Name="BetonCombo" Margin="5"  Grid.Column="0" Padding="2" HorizontalAlignment="Center" Width="150" SelectedValuePath="Content" SelectionChanged="BetonCombo_SelectionChanged">
    <ComboBoxItem>C16/20 (B20)</ComboBoxItem>
    <ComboBoxItem>C20/25 (B25)</ComboBoxItem>
    <ComboBoxItem>C25/30 (B30)</ComboBoxItem>
    <ComboBoxItem IsSelected="True">C30/37 (B37)</ComboBoxItem>
    <ComboBoxItem>C35/45 (B45)</ComboBoxItem>
</ComboBox>

private void BetonCombo_SelectionChanged(object sender, SelectionChangedEventArgs e)
       {

           int mBetonIndex = BetonCombo.SelectedIndex;

               double[] Fck = new double[5];
               Fck[0] = 20;
               Fck[1] = 25;
               Fck[2] = 30;
               Fck[3] = 37;
               Fck[4] = 45;

               double mFck = Fck[mBetonIndex];
               fck.Text = mFck.ToString() + " MPa";
       }

System.NullReferenceException: 'Object reference not set to an instance of an object.'