using System;

using System.Diagnostics;

using System.Threading.Tasks;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        Stopwatch watch = new Stopwatch();

        watch.Start();

        var list = NotWhenAllOneAsync().Result;

        watch.Stop();

        Console.WriteLine("NotWhenAllOneAsync, total time " + watch.ElapsedMilliseconds);

        watch.Restart();

        var array = WithWhenAllAsync().Result;

        watch.Stop();

        Console.WriteLine("WithWhenAllAsync, total time " + watch.ElapsedMilliseconds);

    }

​

    static async Task<List<int>> NotWhenAllOneAsync()

    {

        var one = DelayedInt(1);

        var two = DelayedInt(2);

        var thr = DelayedInt(3);

        return new List<int>

        {

            await one, await two, await thr

        };

    }

​

    static Task<int[]> WithWhenAllAsync()

    {

        var one = DelayedInt(1);

        var two = DelayedInt(2);

        var thr = DelayedInt(3);

        return Task.WhenAll(one, two, thr);

    }

​

    static async Task<int> DelayedInt(int value)

    {

        await Task.Delay(500);

        return value;

    }

}