reordering.cs

using System;
using System.Threading.Tasks;

namespace MemoryReordering
{
    class Program
    {
        private static int x;
        private static int y;

        private static int r1;
        private static int r2;

        private static void Foo()
        {
            x = 1;
            r1 = y;
        }

        private static void Bar()
        {
            y = 1;
            r2 = x;            
        }
    
        static void Main(string[] args)
        {
            for (int i = 0; i < 10000; i++)
            {
                x = 0;
                y = 0;
                r1 = 0;
                r2 = 0;
                
                var t1 = Task.Run(() => Foo());
                var t2 = Task.Run(() => Bar());

                Task.WaitAll(t1, t2);
                
                if (r1 == 0 && r2 == 0)
                {
                    throw new InvalidOperationException("WTF???");
                }
            }
        }
    }
}

The funny thing that it will not fail if start program only at 2 cores.

Oh, it fails but (often) needs more than 10k iterations :D

@NoofSaeidh It will never fail if you start it only at one core :)

@retran of course. More cores more bugs! :)