DLL Conflict/Crash with PyQt6 and onnxruntime

[Phil Thompson]

On 23/11/2025 00:52, Marius Wanko wrote:
> Hi,
> 
> I encountered an access violation (0xC0000005) when importing 
> onnxruntime
> along PyQt6 on Windows 10/11. On the python end this raises 
> "ImportError:
> DLL load failed while importing onnxruntime_pybind11_state: A dynamic 
> link
> library (DLL) initialization routine failed."
> 
> I tracked it down to the system DLLs vcruntime140*.dll and 
> msvcp140*.dll,
> which are bundled in the PyQt6 PyPI wheels (Qt6/bin/) whereas 
> onnxruntime
> seem to be compiled against the corresponding system dlls (I checked
> dependencies). If PyQt6 is imported first, the crash occurs when
> onnxruntime initializes. The Windows SDK debugger shows me
> "MSVCP140!mtx_do_lock" in the stack trace. When I delete the bundled 
> dlls,
> the error disappears and onnxruntime works as expected.
> 
> I just wanted to communicate this, I'm not going to argue whether the
> bundling is a good idea or not.
> 
> Marius

I don't know if it is a good idea either. Does anybody know what current 
best practice is?

Historically I don't think you could depend on those DLLs being already 
installed. I would hope that that has changed.

Phil