using System;

using System.Diagnostics;

using System.Threading;

using System.Threading.Tasks;

using System.Linq;

​

public class Program

{

    public static async Task Main()

    {

        Task[] tasks = Enumerable.Range(1, 100_000).Select(async _ =>

        {

            await Task.Delay(1000);

        }).ToArray();

        Console.WriteLine($"Tasks: {tasks.Count(t => t.IsCompleted):#,0} / {tasks.Length:#,0}");

        Thread.Sleep(500);

        Console.WriteLine($"Threads.Count: {Process.GetCurrentProcess().Threads.Count:#,0}");

        await Task.WhenAll(tasks);

        Console.WriteLine($"Tasks: {tasks.Count(t => t.IsCompleted):#,0} / {tasks.Length:#,0}");

    }

}

​