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.NET Forum / Languages / C# / February 2008Closing an unmanaged DLL
I have a C# app that must use a C# class library, which in turn references an unmanaged C++ DLL. My code interacts briefly with the C# class library, after which my code must fully release it, retaining no references to either the class library or the DLL (which the class library uses via DllImport). Unfortunately, neither the class library nor the C++ DLL are under my control, and I can't change the constraints above. I've managed to release the C# dll by interacting with it in a temporary AppDomain, which I then unload. However, my process still retains a reference to the C++ DLL. How can I either avoid that, or close the reference? The only way I can think of to do this would be to not use the P/Invoke layer directly, and instead use calls to LoadLibrary/FreeLibrary along with GetProcAddress to get a pointer to the functions you are calling, then call the static GetDelegateForFunctionPointer method on the Marshal class to get a delegate which you can call which will perform the call to the unmanaged code.  Signature- Nicholas Paldino [.NET/C# MVP] - mvp@spam.guard.caspershouse.com >I have a C# app that must use a C# class library, which in turn > references an unmanaged C++ DLL. My code interacts briefly with the [quoted text clipped - 9 lines] > retains a reference to the C++ DLL. How can I either avoid that, or > close the reference? On Feb 22, 2:05 pm, "Nicholas Paldino [.NET/C# MVP]" <m...@spam.guard.caspershouse.com> wrote: > The only way I can think of to do this would be to not use the P/Invoke > layer directly, and instead use calls to LoadLibrary/FreeLibrary along with [quoted text clipped - 24 lines] > > retains a reference to the C++ DLL. How can I either avoid that, or > > close the reference? Nicholas, Unfortunately, neither the class library nor the managed code are under my control. I can't change how they're written. As a last resort, I can interact with them in another process entirely, then kill that process, but I really don't want to do that. The old analogy of using a cannon to kill a gnat comes to mind. > On Feb 22, 2:05 pm, "Nicholas Paldino [.NET/C# MVP]" > <m...@spam.guard.caspershouse.com> wrote: [quoted text clipped - 39 lines] > kill that process, but I really don't want to do that. The old > analogy of using a cannon to kill a gnat comes to mind. You can get the module handle by calling GetModuleHandle and use this handle in a call to FreeLibrary. Here are the DllImport declarations and a usage sample. [DllImport("kernel32")] static extern IntPtr GetModuleHandle(string module); [DllImport("kernel32")] [return: MarshalAs(UnmanagedType.Bool)] static extern bool FreeLibrary(IntPtr handle); ... IntPtr HModule = GetModuleHandle("nativeModule.dll"); bool success = FreeLibrary(HModule); if(success) ... else ... Willy. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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