Parallel calls to Repository.ObjectDatabase.CreateBlob with identical contents fails.

Comienza en Repository.ObjectDatabase.CreateBlob y ejecuta la reproducción de C# contra un repositorio bare. Traza la ruta paralela para contenidos idénticos y los resultados FILE_EXISTS y null-blob reportados. Se considera completado cuando las llamadas concurrentes finalizan sin ninguno de los dos fallos y crean el blob esperado.

I would like to insert blobs from memory into an object database in parallel (based on the technique described at http://stackoverflow.com/a/16244234). This works fine most of the time, but is subject to race conditions if the contents are the same. There are two classes of errors I observe:
1. Exception due to FILE_EXISTS conflict when trying to create the directory with the first two characters of the OID under objects.
2. NULL blob returned from CreateBlob.

Here's some example code to reproduce the problem:

using System;
using System.Text;
using System.IO;
using System.Threading.Tasks;
using LibGit2Sharp;

namespace GitODBStress
{
    class Program
    {
        static void Main()
        {

            string repoPath = Path.Combine(Path.GetTempPath(), "Git_Parallel_Odb");
            int iterationCount = 100;

            if (!Directory.Exists(repoPath))
            {
                Directory.CreateDirectory(repoPath);
            }

            var path = Repository.Init(repoPath, isBare:true);
            Console.WriteLine("Made repo at {0}", path);

            var repo = new Repository(path);

            var tasks = new Task[2];
            for (int i = 0; i < iterationCount; ++i)
            {
                var iter = i;
                byte[] buf = Encoding.ASCII.GetBytes("foo" + iter.ToString());
                for (int taskNo = 0; taskNo < 2; ++taskNo)
                {
                    tasks[taskNo] = Task.Factory.StartNew(() =>
                        {
                            MemoryStream ms = new MemoryStream(buf);
                            for (; ; )
                            {
                                try
                                {
                                    var blob = repo.ObjectDatabase.CreateBlob(ms);
                                    if (blob == null)
                                    {
                                        Console.WriteLine("ERROR: NULL blob on iteration {0}", iter);
                                        continue;
                                    }

                                    break;
                                }
                                catch (LibGit2SharpException e)
                                {
                                    Console.WriteLine("ERROR: Caught LibGit2SharpException on iteration {0}: {1}", iter, e.Message);
                                    if (e.Message.Contains("Cannot create a file when that file already exists."))
                                    {
                                        continue;
                                    }
                                }
                            }
                        });
                }

                Task.WaitAll(tasks);
            }

            repo.Dispose();

            // clean up temp repo files
            var files = Directory.GetFiles(repoPath, "*.*", SearchOption.AllDirectories);
            foreach (var f in files)
            {
                var attrib = File.GetAttributes(f);
                if (attrib.HasFlag(FileAttributes.ReadOnly))
                {
                    File.SetAttributes(f, attrib & ~FileAttributes.ReadOnly);
                }
            }

            Directory.Delete(repoPath, true);
        }
    }
}

Thanks!