using System;

using System.Collections.Generic;

using System.Collections;

using System.Linq;

using System.Linq.Expressions;

using System.Threading.Tasks;

using System.Threading;

public class Program

{

    public static void Main()

    {

        AsyncMain().Wait();

    }

    public static async Task AsyncMain()

    {

        // perform 10 long running tasks concurrently

        Console.WriteLine($"Started at {DateTime.Now}");

        var tasks = new List<Task>();

        for(var i = 0; i < 10; i++)

        {

            //tasks.Add(LongRunningTask(i));

            tasks.Add(CpuHeavyComputation(i));

        }

        await Task.WhenAll(tasks);

        Console.WriteLine($"Completed at {DateTime.Now}");

    }

    public static async Task LongRunningTask(int i)

    {

        await Task.Delay(2000);

        Console.WriteLine(i);

    }

    public static async Task CpuHeavyComputation(int i)

    {

        Thread.Sleep(2000); // heavy CPU operation

        Console.WriteLine(i);

    }

}