[Looking for Suggestion] Unable to find assembly: SkiaSharp #2589

chaojian-zhang · 2025-04-30T13:45:36Z

chaojian-zhang
Apr 30, 2025

(Originally an issue: #2588)

Hi, thanks for the great library! It has been tremendously helpful in both my personal and professional life!

Right now I am encountering a problem that might not be pythonnet specific but is not obvious to solve and encountered when I use Pythonnet. Specifically, when my project references SkiaSharp which contains native dlls, pythonnet will not be able to load everything properly - it locates the entry assembly fine, but the dependencies are not loaded. The initial import is ok but during runtime an exception is thrown.

Would love to hear any suggestions on solving this problem.

Environment

Pythonnet version: 3.0.5
Python version: 3.11.9 64bit
Operating System: Windows 7 64-bit

Below is the entry assembly, which directly references SkiaSharp.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net8.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="SkiaSharp" Version="3.119.0" />
  </ItemGroup>
</Project>

using SkiaSharp;

namespace PythonNetSkiaSharpProblem
{
    public class Program
    {
        public static void Main(string[] args)
        {
            try
            {
                var info = new SKImageInfo(width: 64, height: 64);
                using var surface = SKSurface.Create(info);
                SKCanvas canvas = surface.Canvas;
                canvas.Clear(new SKColor(red: 0, green: 200, blue: 200, alpha: 255));
                using SKImage image = surface.Snapshot();
                using SKData pngData = image.Encode(SKEncodedImageFormat.Png, quality: 100);
                const string outputPath = "filled64.png";
                using var stream = File.OpenWrite(outputPath);
                pngData.SaveTo(stream);

                System.Console.WriteLine($"Saved {outputPath}");
            }
            catch (Exception e)
            {
                Console.WriteLine(e);
            }   
        }
    }
}

And this is how I am referencing the entry assembly, from some location outside the published folder (notice the same problem happens even if this script is placed directly inside the published folder).

import sys
sys.path.insert(0, r"C:\Users\Charles Zhang\Desktop\Temp\PythonNetSkiaSharpProblem\PythonNetSkiaSharpProblem\bin\Debug\net8.0")

import pythonnet
pythonnet.load("coreclr")

import clr
clr.AddReference("PythonNetSkiaSharpProblem")

from PythonNetSkiaSharpProblem import Program
Program.Main([]) # Exception in stack

Output:

System.TypeInitializationException: The type initializer for 'SkiaSharp.SKImageInfo' threw an exception.
 ---> System.DllNotFoundException: Unable to load DLL 'libSkiaSharp' or one of its dependencies: The specified module could not be found. (0x8007007E)
   at SkiaSharp.SkiaApi.sk_colortype_get_default_8888()
   at SkiaSharp.SkiaApi.sk_colortype_get_default_8888()
   at SkiaSharp.SKImageInfo..cctor()
   --- End of inner exception stack trace ---
   at SkiaSharp.SKImageInfo..ctor(Int32 width, Int32 height)
   at PythonNetSkiaSharpProblem.Program.Main(String[] args) in C:\Users\Charles Zhang\Desktop\Temp\PythonNetSkiaSharpProblem\PythonNetSkiaSharpProblem\Program.cs:line 11

This is likely due to this folder structure:

└───net8.0
    │   PythonNetSkiaSharpProblem.deps.json
    │   PythonNetSkiaSharpProblem.dll
    │   PythonNetSkiaSharpProblem.exe
    │   PythonNetSkiaSharpProblem.pdb
    │   PythonNetSkiaSharpProblem.runtimeconfig.json
    │   SkiaSharp.dll
    │
    └───runtimes
        ├───osx
        │   └───native
        │           libSkiaSharp.dylib
        │
        ├───win-arm64
        │   └───native
        │           libSkiaSharp.dll
        │
        ├───win-x64
        │   └───native
        │           libSkiaSharp.dll
        │
        └───win-x86
            └───native
                    libSkiaSharp.dll

See: https://github.com/Charles-Zhang-Python/PythonNetSkiaSharpProblem

This might be related to #468 but is somewhat different since I am not loading the dll directly, and everything is .Net 8 properly.

chaojian-zhang · 2025-04-30T13:58:33Z

chaojian-zhang
Apr 30, 2025
Author

Notice a workaround is to copy libSkiaSharp.dll directly to the root of the published folder.
But this won't work cross-platform and also if we have many similar libraries that exhibit similar behavior then it's not convenient.

0 replies

filmor · 2025-05-02T13:10:10Z

filmor
May 2, 2025
Maintainer

Your link is not working
You are creating an executable, not a library
Please try using dotnet publish

2 replies

filmor May 2, 2025
Maintainer

I tried it, publishing as dotnet publish -r win-x64 -o some_place works fine and publishes the correct libSkiaSharp.dll along with it. I can't test it further without hassle as there is no Linux version in the nuget.

chaojian-zhang May 2, 2025
Author

Hi @filmor, thanks for the reply. I've fixed the repo link.

I am aware that dotnet publish with a target runtime will work. That's because it will copy the specific dlls to the root folder. It's however just workarounded the problem, rather than fixed it. Like I commented out above.
However this will not work with a non-platform dependent publish nor a general build (instead of publishing). To test it, you don't need to have linux version per se: just do Build All in visual studio and use that output in bin/debug/net8.0-windows as the folder to test against.

Regarding "You are creating an executable, not a library", that shouldn't be a problem since in dotnet all executables are just dlls, the .exe is just a thin shells that calls into the .dll. In python (with pythonnet) we just load the dll.

In the meantime, I did find a more robust way to load the dlls from the python side. One workaround is to add below class and make available to python script:

public sealed class PluginLoadContext : AssemblyLoadContext
  {
      readonly AssemblyDependencyResolver resolver;
      public PluginLoadContext(string pluginMainDll)
          => resolver = new(pluginMainDll);
      protected override Assembly? Load(AssemblyName name)
          => resolver.ResolveAssemblyToPath(name) is { } p
              ? LoadFromAssemblyPath(p)
              : null;
      protected override IntPtr LoadUnmanagedDll(string libName)
          => resolver.ResolveUnmanagedDllToPath(libName) is { } p
              ? LoadUnmanagedDllFromPath(p)
              : IntPtr.Zero;
  }

Then, instead of loading using clr.AddReference, call below:

ctx = PluginLoadContext(str(dll_path))
asm = ctx.LoadFromAssemblyPath(str(dll_path)) # Equivalent to clr.AddReference(asm), notice "import" works out of the box due to Pythonnet's hook into the import process

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[Looking for Suggestion] Unable to find assembly: SkiaSharp #2589

chaojian-zhang Apr 30, 2025

Replies: 2 comments · 2 replies

chaojian-zhang Apr 30, 2025 Author

filmor May 2, 2025 Maintainer

filmor May 2, 2025 Maintainer

chaojian-zhang May 2, 2025 Author

chaojian-zhang
Apr 30, 2025

Replies: 2 comments 2 replies

chaojian-zhang
Apr 30, 2025
Author

filmor
May 2, 2025
Maintainer

filmor May 2, 2025
Maintainer

chaojian-zhang May 2, 2025
Author