using System;

using System.Threading;

using System.Threading.Tasks;

using System.Runtime.CompilerServices;

public class Program

{

    public static void Main()

    {

        printInfo("main before f1");

        var t = f1();

        printInfo("main after f1");

        t.Wait();

        printInfo("main after wait");

    }

    static async Task f1()

    {

        printInfo("f1 before f2");

        await f2();

        printInfo("f1 after f2");

    }

    static async Task f2()

    {

        printInfo("f2 start");

        var t1 = Task.Run(() => printInfo("lambda before delay"));

        printInfo("f2 before delay");       

        await Task.Delay(TimeSpan.FromSeconds(3));

        printInfo("f2 after delay");

        var t2 = Task.Run(() => printInfo("lambda after delay"));

        printInfo("f2 before {t1,t2} await");

        await t1;

        await t2;

        printInfo("f2 end");

    }

    static void printInfo(

        string label = "",

        [CallerMemberName] string methodName = "",

        [CallerLineNumber] int lineNum = -1)

    {

        var thread = Thread.CurrentThread;

        var e = new ArgumentException();

        Console.WriteLine(String.Format("{0,-25}: {1,-8} {2,3};  bgnd={3,-5} pool={4,-5} tid={5,-3};",

            label, methodName, lineNum, thread.IsBackground, thread.IsThreadPoolThread, thread.ManagedThreadId));

    }

​

}