test Task.WaitAll Task.WhenAll Awaiting multiple Tasks with different results Getting return values from Task.WhenAll

program.cs

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;

namespace TestWhenAll.Console
{
    public class Program
    {
        public static void Main(string[] args) => MainAsync(args).GetAwaiter().GetResult();

        public static async Task<int> GetData(int time)
        {
            System.Console.WriteLine($"GetData({time}) START {DateTime.Now:s}");
            await Task.Delay(time * 1000);
            System.Console.WriteLine($"GetData({time}) STOP {DateTime.Now:s}");
            return time;
        }
        private static async Task MainAsync(string[] args)
        {
            // first test
            Stopwatch stopWatch = new Stopwatch();
            System.Console.WriteLine("1 test");
            stopWatch.Start();

            int var1 = await GetData(3);
            int var2 = await GetData(5);
            int var3 = await GetData(10);

            stopWatch.Stop();

            System.Console.WriteLine($"End 1 - {var1} {var2} {var3} elapsed: {stopWatch.ElapsedMilliseconds}");

            stopWatch.Reset();
            System.Console.WriteLine("\n\n 2 test");
            stopWatch.Start();
            
            await Task.WhenAll(GetData(3), GetData(5), GetData(10));

             var1 = await GetData(3);
             var2 = await GetData(5);
             var3 = await GetData(10);

            stopWatch.Stop();
            System.Console.WriteLine($"End 2 - {var1} {var2} {var3} elapsed: {stopWatch.ElapsedMilliseconds}");

            stopWatch.Reset();
            System.Console.WriteLine("\n\n3 test");
            stopWatch.Start();

            var t2GetData1 = GetData(3);
            var t2GetData3 = GetData(5);
            var t2GetData5 = GetData(10);

            await Task.WhenAll(t2GetData1, t2GetData3, t2GetData5);

            var2 = await t2GetData1;
            var1 = await t2GetData3;
            var3 = await t2GetData5;

            stopWatch.Stop();
            System.Console.WriteLine($"End 3 - {var1} {var2} {var3} elapsed: {stopWatch.ElapsedMilliseconds}");
            
            stopWatch.Reset();
            System.Console.WriteLine("\n\n4 test");
            stopWatch.Start();

            var t2GetData1b = GetData(3);
            var t2GetData3b = GetData(5);
            var t2GetData5b = GetData(10);

            Task.WaitAll(new Task[]{t2GetData1b, t2GetData3b, t2GetData5b},CancellationToken.None);

            var2 = await t2GetData1b;
            var1 = await t2GetData3b;
            var3 = await t2GetData5b;

            stopWatch.Stop();
            System.Console.WriteLine($"End 4 - {var1} {var2} {var3} elapsed: {stopWatch.ElapsedMilliseconds}");

            stopWatch.Reset();
            System.Console.WriteLine("\n\n 5 test");
            stopWatch.Start();

            //result order?
            int[] results = await Task.WhenAll(GetData(10), GetData(5), GetData(3));

            stopWatch.Stop();
            System.Console.WriteLine($"End 5 -  {results[0]} {results[1]} {results[2]} elapsed: {stopWatch.ElapsedMilliseconds}");
            
            System.Console.ReadLine();
        }
    }
}