Simple proof that GUID is not unique [closed]

Answer 1

I don't understand why no one has mentioned upgrading your graphics card... Surely if you got a high-end NVIDIA Quadro FX 4800 or something (192 CUDA cores) this would go faster...

Of course if you could afford a few NVIDIA Qadro Plex 2200 S4s (at 960 CUDA cores each), this calculation would really scream. Perhaps NVIDIA would be willing to loan you a few for a "Technology Demonstration" as a PR stunt?

Surely they'd want to be part of this historic calculation...

Answer 2

Kai, I have provided a program that will do what you want using threads. It is licensed under the following terms: you must pay me $0.0001 per hour per CPU core you run it on. Fees are payable at the end of each calendar month. Please contact me for my paypal account details at your earliest convenience.

using System;
using System.Collections.Generic;
using System.Linq;

namespace GuidCollisionDetector
{
    class Program
    {
        static void Main(string[] args)
        {
            //var reserveSomeRam = new byte[1024 * 1024 * 100];     // This indeed has no effect.

            Console.WriteLine("{0:u} - Building a bigHeapOGuids.", DateTime.Now);
            // Fill up memory with guids.
            var bigHeapOGuids = new HashSet<Guid>();
            try
            {
                do
                {
                    bigHeapOGuids.Add(Guid.NewGuid());
                } while (true);
            }
            catch (OutOfMemoryException)
            {
                // Release the ram we allocated up front.
                // Actually, these are pointless too.
                //GC.KeepAlive(reserveSomeRam);
                //GC.Collect();
            }
            Console.WriteLine("{0:u} - Built bigHeapOGuids, contains {1} of them.", DateTime.Now, bigHeapOGuids.LongCount());


            // Spool up some threads to keep checking if there's a match.
            // Keep running until the heat death of the universe.
            for (long k = 0; k < Int64.MaxValue; k++)
            {
                for (long j = 0; j < Int64.MaxValue; j++)
                {
                    Console.WriteLine("{0:u} - Looking for collisions with {1} thread(s)....", DateTime.Now, Environment.ProcessorCount);
                    System.Threading.Tasks.Parallel.For(0, Int32.MaxValue, (i) =>
                    {
                        if (bigHeapOGuids.Contains(Guid.NewGuid()))
                            throw new ApplicationException("Guids collided! Oh my gosh!");
                    }
                    );
                    Console.WriteLine("{0:u} - That was another {1} attempts without a collision.", DateTime.Now, ((long)Int32.MaxValue) * Environment.ProcessorCount);
                }
            }
            Console.WriteLine("Umm... why hasn't the universe ended yet?");
        }
    }
}

PS: I wanted to try out the Parallel extensions library. That was easy.

And using OutOfMemoryException as control flow just feels wrong.

EDIT

Well, it seems this still attracts votes. So I've fixed the GC.KeepAlive() issue. And changed it to run with C# 4.

And to clarify my support terms: support is only available on the 28/Feb/2010. Please use a time machine to make support requests on that day only.

EDIT 2 As always, the GC does a better job than I do at managing memory; any previous attempts at doing it myself were doomed to failure.

Answer 3

You could hash the GUIDs. That way, you should get a result much faster.

Oh, of course, running multiple threads at the same time is also a good idea, that way you'll increase the chance of a race condition generating the same GUID twice on different threads.

Answer 4

Have you tried begin = begin + new BigInteger((long)1) in place of begin++?

Answer 5

Personally, I think the "Big Bang" was caused when two GUIDs collided.

Answer 6

The only solution to prove GUIDs are not unique would be by having a World GUID Pool. Each time a GUID is generated somewhere, it should be registered to the organization. Or heck, we might include a standardization that all GUID generators needs to register it automatically and for that it needs an active internet connection!