using System;

using System.Threading;

using System.Threading.Tasks;

public class Program

{

    public static void Main()

    {

        var mres = new ManualResetEventSlim();

        Console.WriteLine(Environment.CurrentManagedThreadId);

        var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);

        var t = Task.WhenAll(tcs.Task);

        t.ContinueWith(delegate

        {

            Console.WriteLine(Environment.CurrentManagedThreadId);

            mres.Set();

        }, TaskContinuationOptions.ExecuteSynchronously);

        tcs.SetResult(true);

        mres.Wait();

    }

}