using System;

using System.Threading.Tasks;

using System.Linq;

using System.Diagnostics;

​

const int DELAY_MS = 100;

​

var sw = new Stopwatch();

sw.Start();

var t1 = DelayAndReturn(1);

var t2 = DelayAndReturn(2);

​

await t1.ConfigureAwait(false);

await t2.ConfigureAwait(false);

​

Console.WriteLine($"{sw.Elapsed}");

sw.Restart();

​

var t3 = Task.Delay(DELAY_MS).ContinueWith(_ => 3);

​

await Task.Delay(DELAY_MS).ConfigureAwait(false);

await t3.ConfigureAwait(false);

​

Console.WriteLine($"{sw.Elapsed}");

sw.Restart();

​

await Task.WhenAll([

    DelayAndReturn(5),

    DelayAndReturn(6),

]).ConfigureAwait(false);

​

Console.WriteLine($"{sw.Elapsed}");

sw.Restart();

​

await Task.WhenAll([

    Task.Run(async () => { await Task.Delay(DELAY_MS).ConfigureAwait(false); return 7; }),

    DelayAndReturn(8),

]).ConfigureAwait(false);

​

Console.WriteLine($"{sw.Elapsed}");

sw.Restart();

​

// nicht parallel ist es nur so:

var t9 = DelayAndReturn(9);

​

await t9.ConfigureAwait(false);

await DelayAndReturn(10).ConfigureAwait(false);

​

Console.WriteLine($"{sw.Elapsed}");

​

async Task<int> DelayAndReturn(int x) { await Task.Delay(DELAY_MS); return x; }