Directory.Delete(string, bool) throws StackOverflowException

[tahirkilic]

Description

Directory.Delete(string, bool) throws a StackOverflowException if the nesting depth of subdirectories is huge (in my case 14000).

Reproduction Steps

• Create nested subdirectories like below:

    DirectoryInfo topMost = new DirectoryInfo("C:\\temp");
    int depth = 14000;

    DirectoryInfo subDir = topMost;
    for (int i = 0; i < depth; i++)
    {
        subDir = subDir.CreateSubdirectory("a");
    }

• Then try to delete the top most directory

Directory.Delete(topMost.FullName, true);

Expected behavior

Topmost directory and its all subdirectories are deleted successfully.

Actual behavior

A StackOverflowException is thrown with the following stacktrace:

Stack overflow.
   at System.String.Concat(System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>)
   at System.IO.Path.JoinInternal(System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>)
   at System.IO.Path.CombineInternal(System.String, System.String)
   at System.IO.Path.Combine(System.String, System.String)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   ....
   ....

Regression?

No response

Known Workarounds

No response

Configuration

dotnet version: 6.0.301

operating system: Windows 10 version 21H2

Other information

No response

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Directory.Delete(string, bool) throws a StackOverflowException if the nesting depth of subdirectories is huge (in my case 14000).

Reproduction Steps

• Create nested subdirectories like below:

    DirectoryInfo topMost = new DirectoryInfo("C:\\temp");
    int depth = 14000;

    DirectoryInfo subDir = topMost;
    for (int i = 0; i < depth; i++)
    {
        subDir = subDir.CreateSubdirectory("a");
    }

• Then try to delete the top most directory

Directory.Delete(topMost.FullName, true);

Expected behavior

Topmost directory and its all subdirectories are deleted successfully.

Actual behavior

A StackOverflowException is thrown with the following stacktrace:

Stack overflow.
   at System.String.Concat(System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>)
   at System.IO.Path.JoinInternal(System.ReadOnlySpan`1<Char>, System.ReadOnlySpan`1<Char>)
   at System.IO.Path.CombineInternal(System.String, System.String)
   at System.IO.Path.Combine(System.String, System.String)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   at System.IO.FileSystem.RemoveDirectoryRecursive(System.String, WIN32_FIND_DATA ByRef, Boolean)
   ....
   ....

Regression?

No response

Known Workarounds

No response

Configuration

dotnet version: 6.0.301

operating system: Windows 10 version 21H2

Other information

No response

Author:	tahirkilic
Assignees:	-
Labels:	area-System.IO, untriaged
Milestone:	-

[GoldenretriverYT]

I dont think this is a bug as you have specified recursive: true and StackOverflows are a risk of recursive actions.

As workaround you could write your own, iterative, method that does that. But if you are honestly using 14 000 nested directories, there is something absolutely wrong with your approach anyways.

[tahirkilic]

14000 nested directories are not used in production. I have created them to demonstrate the problems of recursion. After the demo, I have tried to delete the directory tree and stumbled upon this bug.

Although the parameter is called "recursive", recursion is an implementation detail. The deletion could be implemented in an iterative way too.
By the way, the documentation of Delete(string, bool) method does not mention any risks of recursion.

[danmoseley]

I suppose this method could probe for stack space in order to fail more usefully.

[aevitas]

I suppose this method could probe for stack space in order to fail more usefully.

How would it do that? Could a method figure out that it itself had been called N times, and if so how would it know when to terminate execution? Would you have the method walk the stack every time it's called, and if so, wouldn't that be a huge performance impact on non-academic usage of the method? I'm genuinely curious how this could be done in a sensible way.

[jkotas]

We have methods for that: RuntimeHelpers.TryEnsureSufficientExecutionStack and RuntimeHelpers.EnsureSufficientExecutionStack. There methods are very efficient, they do not do expensive operations like stackwalks.

[eriawan]

@adamsitnik

Is this issue already taken or is currently the work? If it is not, I would like to try to take this issue by assigning this issue to me.

I have an idea to safely recurse the folders without wasting stack, using a bit of fixed point combinator. 🙂
I may want to promote/propose a new class to feature that later, because it is quite helpful to ease recursion.

[danmoseley]

@eriawan I will assign to you. thanks for working on this!

[danmoseley]

I have an idea to safely recurse the folders without wasting stack, using a bit of fixed point combinator.

To fix this specific bug, it is probably only needed to call RuntimeHelpers. I suggest to make that limited fix in its own PR first. If you want to avoid recursion entirely, that would be a larger change, and would need some perf measurements to demonstrate it was worthwhile.