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using System;
using System.Threading.Tasks;

internal class Program
{
    public static void Main(string[] args)
    {
        independentTasks();

        Task3OnlyAfterTask1();

        Task3AfterTask1AndTask2();

        Task3AfterTask1OrTask2();
    }

    private static void Task3AfterTask1OrTask2()
    {
        Task step1Task = Task.Run(() => Step1());
        Task step2Task = Task.Run(() => Step2());
        Task step3Task = Task.Factory.ContinueWhenAny(
            new[] { step1Task, step2Task }, 
            (previousTask) => Step3());

        step3Task.Wait();
    }

    private static void Task3AfterTask1AndTask2()
    {
        Task step1Task = Task.Run(() => Step1());
        Task step2Task = Task.Run(() => Step2());
        Task step3Task = Task.Factory.ContinueWhenAll(new[] { step1Task, step2Task }, (previousTasks) => Step3());

        step3Task.Wait();
    }

    private static void Task3OnlyAfterTask1()
    {
        Task step1Task = Task.Run(() => Step1());
        Task step2Task = Task.Run(() => Step2());
        Task step3Task = step1Task.ContinueWith((previousTask) => Step3());

        Task.WaitAll(step2Task, step3Task);
    }

    private static void independentTasks()
    {
        // metody niezależne
        Parallel.Invoke(Step1, Step2, Step3);
    }

    private static void Step1()
    {
        Console.WriteLine("Step1");
    }

    private static void Step2()
    {
        Console.WriteLine("Step2");
    }

    private static void Step3()
    {
        Console.WriteLine("Step3");
    }
}