WhenAllWorkflow.cs

async Task RunWorkflow()
{
    var stopwatch = Stopwatch.StartNew();

    // Task 1 takes 2 seconds to be done.
    var task1 =  Task.Delay(2000)
        .ContinueWith(task => Completed("Task 1", stopwatch.Elapsed));

    // Task 2 takes 3 seconds to be done.
    var task2 = Task.Delay(3000)
        .ContinueWith(task => Completed("Task 2", stopwatch.Elapsed));

    // Task 3 takes 1 second to be done.
    var task3 = Task.Delay(1000)
        .ContinueWith(task => Completed("Task 3", stopwatch.Elapsed));

    await Task.WhenAll(task1, task2, task3);
    
    // Print the final result.
    Completed("Workflow: ", stopwatch.Elapsed);
    stopwatch.Stop();
}

void Completed(string name, TimeSpan time)
{
    Console.WriteLine($"{name} : {time}");
}