throw LibGit2SharpException or repo.Head.TIp==null while parallel

Updated. Code simplified

// use LibGit2Sharp.0.16.0.0 from nuget
// https://github.com/torvalds/linux
var gitpath = @"path/to/linux/source";

var times = 10;
for (int i = 0; i < times; i++)
{
    Task.Run(() =>
    {
        using (var repo = new Repository(gitpath))
        {
            // sometimes throw LibGit2SharpException here
            // An exception of type 'LibGit2Sharp.LibGit2SharpException' occurred in LibGit2Sharp.dll but was not handled in user code
            // Additional information: An error was raised by libgit2. Category = Os (Error).
            // Failed to mmap. No data written: Not enough storage is available to process this command.
            foreach (var commit in repo.Commits)
            {
            }
        }
    });
}

while (true)
{
    using (var repo = new Repository(gitpath))
    {
        // sometimes repo.Head.Tip == null
        repo.Head.Tip.ToString();
    }
}

先使用 Repository(gitpath)、repo.Commits 和 repo.Head.Tip 進行平行重現，然後使用 LibGit2Sharp 0.16.0.0 在 Linux repository 上執行。調查並行建構或存取 repository 是否會導致 mmap 失敗和 null tip；當回報的平行操作不再產生這兩種現象中的任何一種時，即視為完成；如果專案有合適的測試位置，則加入 regression test。