How do I prevent and/or handle a StackOverflowException?

Question

I would like to either prevent or handle a `StackOverflowException` that I am getting from a call to the `XslCompiledTransform.Transform` method within an `Xsl Editor` I am writing. The problem seems to be that the user can write an `Xsl script` that is infinitely recursive, and it just blows up on the call to the `Transform` method. (That is, the problem is not just the typical programmatic error, which is usually the cause of such an exception.) Is there a way to detect and/or limit how many recursions are allowed? Or any other ideas to keep this code from just blowing up on me?

Accepted Answer

From Microsoft:

Starting with the .NET Framework version 2.0, a StackOverflowException object cannot be caught by a try-catch block and the corresponding process is terminated by default. Consequently, users are advised to write their code to detect and prevent a stack overflow. For example, if your application depends on recursion, use a counter or a state condition to terminate the recursive loop.

I'm assuming the exception is happening within an internal .NET method, and not in your code.

You can do a couple things.

- Write code that checks the xsl for infinite recursion and notifies the user prior to applying a transform (Ugh).

- Load the XslTransform code into a separate process (Hacky, but less work).

You can use the Process class to load the assembly that will apply the transform into a separate process, and alert the user of the failure if it dies, without killing your main app.

EDIT: I just tested, here is how to do it:

MainProcess:

```
// This is just an example, obviously you'll want to pass args to this.
Process p1 = new Process();
p1.StartInfo.FileName = "ApplyTransform.exe";
p1.StartInfo.UseShellExecute = false;
p1.StartInfo.WindowStyle = ProcessWindowStyle.Hidden;

p1.Start();
p1.WaitForExit();

if (p1.ExitCode == 1)    
   Console.WriteLine("StackOverflow was thrown");
```

ApplyTransform Process:

```
class Program
{
    static void Main(string[] args)
    {
        AppDomain.CurrentDomain.UnhandledException += new UnhandledExceptionEventHandler(CurrentDomain_UnhandledException);
        throw new StackOverflowException();
    }

// We trap this, we can't save the process, 
    // but we can prevent the "ILLEGAL OPERATION" window 
    static void CurrentDomain_UnhandledException(object sender, UnhandledExceptionEventArgs e)
    {
        if (e.IsTerminating)
        {
            Environment.Exit(1);
        }
    }
}
```

How do I prevent and/or handle a StackOverflowException?

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