using System;

using System.Collections.Generic;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public async static Task Main()

    {

        /*

        var list = new Task[5];

        for (var i = 0; i < 5; i++)

        {

            list[i] = DoSmth(i);

        }   

        Task.WaitAll(list);

        Parallel.For(0, 10, (idx) => {

            DoSmth(idx);

        });

        */

        await Do();

        Console.WriteLine("main done");

    }

    private static async Task Do()

    {

        var list = new Task[5];

        for (var i = 0; i < list.Length; i++)

        {

            list[i] = DoSmth(i);

        }

        await Task.WhenAll();

    }

    private static async Task LoadSmth() => await Task.Run(() => Thread.Sleep(300));

    private static async Task ReadSmth() => await Task.Run(() => Thread.Sleep(100));

    private static async Task DoSmth(int idx)

    {

        await LoadSmth();

        await ReadSmth();

        Console.WriteLine($"{idx} done");

    }

}