Access Denied while deleting the assembly created by a CodeDomProvider compile?

Question

If you use the CodeDomProvider class in .NET after the compilation is complete you can't delete the output assembly. I want to be able to delete the output assembly. File.Delete returns an access denied exception.

string asmPath = Path.Combine(Path.GetTempPath(), Guid.NewGuid().ToString("N") + ".exe");
string keyPath = "some path to a *.snk file that works";
// build compiler
CodeDomProvider dom = CodeDomProvider.CreateProvider("VisualBasic");
CompilerParameters cp = new CompilerParameters();
cp.TreatWarningsAsErrors = false;
cp.GenerateInMemory = false;
cp.GenerateExecutable = true;
cp.CompilerOptions = "/target:winexe /keyfile:\"" + keyPath + "\"";
cp.OutputAssembly = asmPath;
// add all the other assembly references
string netPath = @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\";
cp.ReferencedAssemblies.Add(netPath + @"System.dll");
cp.ReferencedAssemblies.Add(netPath + @"System.Core.dll");
cp.ReferencedAssemblies.Add(netPath + @"System.Data.dll");
cp.ReferencedAssemblies.Add(netPath + @"System.Xml.dll");
CompilerResults cr = dom.CompileAssemblyFromSource(cp, new string[] { code });
if (cr.Errors.Count == 0)
{
    cr.TempFiles.Delete();
    dom.Dispose();
// do stuff
...
//
    File.Delete(asmPath); // fails here Access Denied
}

Edit As a work around I'm using a static constructor on the class that searches the temp folder and deletes previously created assemblies.

Answer 1

I suspect the problem is that the assembly is loaded (in memory), and has the output file open, just as any other assembly that is currently loaded will have a handle to its executable file.

It's also possible (although I consider it unlikely) that the dom instance or the CompilerResults instance has a reference to the opened file. Neither is IDisposable, so I suspect they're not holding the file open.

Possible solutions:

You can compile the assembly to memory. That is, don't output a file. That solves the immediate problem. However, you still have the problem that the compiled assembly remains in memory. There's no way to unload an assembly without tearing down the app domain.

You can create a separate app domain to do the compile, and then communicate the results back to your main app domain. You can then shut down the compiler app domain, which will remove the compiled assembly from memory and also release any file handles that are referencing the file you just created. Your main program can then delete the file in question.