RepositoryStatus sometimes crashes with an AccessViolationException

We've noticed that the GitHub Extension for Visual Studio has been crashing with an AccessViolationException. This often happens when a user previews a PR and the extension calls RetrieveStatus. This exception occurs randomly and is thrown by the git_status_list_new method.

This exception is most easily reproduced using 0.24 or 0.25.0-preview-0033, but it does also happen with 0.23.1 (but I haven't seen it using the repro below).

How to reproduce

1. Clone https://github.com/github/VisualStudio.git to C:\source\github.com\github\VisualStudio\.
2. Compile and run the following code in Release configuration using LibGit2Sharp v0.24:

        static void Main(string[] args)
        {
            var path = @"C:\source\github.com\github\VisualStudio";
            for (int count = 0; count < 1000; count++)
            {
                var status = new Repository(path).RetrieveStatus();
                Console.WriteLine(count + ": " + status.IsDirty);
            }
        }

I tried to create a standalone app, but wasn't able to trigger it with a very simple repo. I'm using the github\VisualStudio one because I'm most familiar it, but it does this with many others as well.

What to expect

The most common exception is as follows:

System.AccessViolationException was unhandled
  HResult=-2147467261
  Message=Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
  Source=LibGit2Sharp
  StackTrace:
       at LibGit2Sharp.Core.NativeMethods.git_status_list_new(git_status_list*& git_status_list, git_repository* repo, GitStatusOptions options)
       at LibGit2Sharp.Core.Proxy.git_status_list_new(RepositoryHandle repo, GitStatusOptions options) in C:\projects\libgit2sharp\LibGit2Sharp\Core\Proxy.cs:line 2931
       at LibGit2Sharp.RepositoryStatus..ctor(Repository repo, StatusOptions options) in C:\projects\libgit2sharp\LibGit2Sharp\RepositoryStatus.cs:line 60
       at LibGit2Sharp.RepositoryExtensions.RetrieveStatus(IRepository repository) in C:\projects\libgit2sharp\LibGit2Sharp\RepositoryExtensions.cs:line 696
       at Libgit2Repro.Program.Main(String[] args) in c:\users\passp\onedrive\documents\visual studio 2015\Projects\Libgit2Repro\Libgit2Repro\Program.cs:line 20
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()

But sometimes NotFoundExceptions are thrown as well.

Related issues / PRs

• Find out why / when LibGit2Sharp is crashing: github/VisualStudio#1315
• GitHub extension crashes when viewing pull requests: github/VisualStudio#1306
• "could not find [file] to open" exception thrown when opening a PR: github/VisualStudio#1326
• Move from LibGit2Sharp v0.24.0 to v0.23.1: github/VisualStudio#1316
• Add using to avoid crash in Release mode: github/VisualStudio#1311

從 RepositoryStatus.cs 和 Core/Proxy.cs 開始，沿著 RetrieveStatus 追蹤到 git_status_list_new。使用 Release 組態中的 LibGit2Sharp v0.24，針對 VisualStudio repository 重現該迴圈，然後調查 AccessViolationException 及相關的 NotFoundExceptions。當擷取 repository 狀態時不再當機，即表示完成。