Load and call dependent C# DLLs in Jupyter Notebook


I'm setting up a Jupyter Notebook within which a C# DLL is called. This works fine when calling a single self contained DLL, but fails when the DLL depends on another C# DLL.

The call to the DLL is done using ctypes and the UnmanagedExports as explained here: https://stackoverflow.com/a/29854281/11588296

The entry DLL's source code is:

using RGiesecke.DllExport;
using System.Runtime.InteropServices;

namespace SimpleCSharpPython
    public class Test
        [DllExport("addDirect", CallingConvention = CallingConvention.Cdecl)]
        public static int TestExport1(int left, int right)
            return left + right;

        [DllExport("addExtern", CallingConvention = CallingConvention.Cdecl)]
        public static int TestExport2(int left, int right)
            return UnderlyingLib.UnderlyingFunc.TestExternExport(left, right);

The underlying DLL is:

namespace UnderlyingLib
    public class UnderlyingFunc
        public static int TestExternExport(int left, int right)
            return left + right;

Finally, the Jupyter Notebook is:

import ctypes
a= ctypes.cdll.LoadLibrary("SimpleCSharpPython.dll")
b= ctypes.cdll.LoadLibrary("UnderlyingLib.dll")
a.addDirect(3, 5)
a.addExtern(3, 4)

The output of the first call (a.addDirect(3, 5)) is 8, as expected. The output of the second call is the following error

OSError                                   Traceback (most recent call last)
<ipython-input-4-c4df87cc7b32> in <module>
----> 1 a.addExtern(3,4)

OSError: [WinError -532462766] Windows Error 0xe0434352

Note the notebook and the 2 DLLs are in the same folder, and the 2 DLLs run fine when called by a C# executable in Visual Studio. I've tried multiple build, path, ctypes calls, but no luck.

Any idea would be greatly appreciated. Let me know if any additional information is required.


1 Answer


I am not an expert but i will try this:

  • remove the loading of the underlying dll in Jupyter ;
  • and ensure the other dll is compiled with a link to the underlying dll so that when Jupyter uses the dll, it does need the underlying dll as only the main dll needs to know it...
answered on Stack Overflow Nov 18, 2020 by BenG73

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