How to dynamically load and unload a native DLL file?

Question

I have a buggy third-party DLL files that, after some time of execution, starts throwing the access violation exceptions. When that happens I want to reload that DLL file. H

Answer 1

Try this

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern IntPtr LoadLibrary(string libname);

[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool FreeLibrary(IntPtr hModule);

//Load
IntPtr Handle = LoadLibrary(fileName);
if (Handle == IntPtr.Zero)
{
     int errorCode = Marshal.GetLastWin32Error();
     throw new Exception(string.Format("Failed to load library (ErrorCode: {0})",errorCode));
}

//Free
if(Handle != IntPtr.Zero)
        FreeLibrary(Handle);

If you want to call functions first you must create delegate that matches this function and then use WinApi GetProcAddress

[DllImport("kernel32.dll", CharSet = CharSet.Ansi)]
private static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName); 


IntPtr funcaddr = GetProcAddress(Handle,functionName);
YourFunctionDelegate function = Marshal.GetDelegateForFunctionPointer(funcaddr,typeof(YourFunctionDelegate )) as YourFunctionDelegate ;
function.Invoke(pass here your parameters);

Answer 2

Create a worker process that communicates via COM or another IPC mechanism. Then when the DLL dies, you can just restart the worker process.

Answer 3

Load the dll, call it, and then unload it till it's gone.

I've adapted the following code from the VB.Net example here.

  [DllImport("powrprof.dll")]
  static extern bool IsPwrHibernateAllowed();

  [DllImport("kernel32.dll")]
  static extern bool FreeLibrary(IntPtr hModule);

  [DllImport("kernel32.dll")]
  static extern bool LoadLibraryA(string hModule);

  [DllImport("kernel32.dll")]
  static extern bool GetModuleHandleExA(int dwFlags, string ModuleName, ref IntPtr phModule);

  static void Main(string[] args)
  {
        Console.WriteLine("Is Power Hibernate Allowed? " + DoIsPwrHibernateAllowed());
        Console.WriteLine("Press any key to continue...");
        Console.ReadKey();
  }

  private static bool DoIsPwrHibernateAllowed()
  {
        LoadLibraryA("powrprof.dll");
        var result = IsPwrHibernateAllowed();
        var hMod = IntPtr.Zero;
        if (GetModuleHandleExA(0, "powrprof", ref hMod))
        {
            while (FreeLibrary(hMod))
            { }
        }
        return result;
  }