Memory leak when marshalling StringWriter between AppDomains.

[johannesg]

Attached is a small program that renders a template to a string using the extension method that uses a StringWriter internally:

        while (!Console.KeyAvailable)
        {
          var result = service.Run("TestTemplate", typeof(TemplateModel), new TemplateModel {Name = "World"});
          Console.WriteLine("Run: {0}. Result: {1}", ++counter, result.Substring(0, 20));
        }

When this loop is called when using a sandbox (IsolatedRazorEngineService), it will quite quickly run out of memory, causing OutOfMemoryException.

The reason is that the internal StringBuilder instance inside the StringWriter will not be GC:ed for several minutes because It is held by the lease manager.

I made a hack in the extension method 'WithWriter' that, instead of using StringWriter, use a MemoryStream + StreamWriter and encode it back to a String. For some reason, using a StreamWriter will not cause memory usage to rise.

I'm not sure if this is actually a bug in .NET or rather an effect of how RazorEngine overrides the management of service lifetime across AppDomains (CrossAppDomainObject).