using System;

using System.Threading.Tasks;

using System.Diagnostics;   

using System.Collections.Generic;               

using System.Linq;

​

public class Program

{       

    public static Task<string> method1(List<int> lst) 

    {       

        var x = lst.FirstOrDefault(p => p == 2145145);

        return Task.FromResult<string>("Method1");          

    }

    public static async Task Main(string[] args)

    {

        var lst = new List<int>();

        for (int i = 0; i<= 3000000;i++)

        {

            lst.Add(i);

        }

        var sw = new Stopwatch();

        sw.Start();

        method1(lst).GetAwaiter().GetResult();

        method1(lst).GetAwaiter().GetResult();

        method1(lst).GetAwaiter().GetResult();

        sw.Stop();

        Console.WriteLine("time: " + sw.ElapsedMilliseconds);

        sw.Reset();

        sw.Start();

        await Task.WhenAll(method1(lst), method1(lst), method1(lst));

        Console.WriteLine("time: " + sw.ElapsedMilliseconds);

    }

}

​