DLL Conflict/Crash with PyQt6 and onnxruntime

[Phil Thompson]

On 23/11/2025 16:21, John Ehresman wrote:
> It sounds like a version specific bug and a quick google search finds
> https://github.com/microsoft/onnxruntime/issues/26599
> 
> John

I've updated the DLLs for Qt v6.10.1. Hopefully that should fix the 
problem.

Phil

>> On Nov 23, 2025, at 11:13 AM, Thomas Caswell <tcaswell at gmail.com> 
>> wrote:
>> 
>> This is the same underlying issue as 
>> https://github.com/matplotlib/matplotlib/issues/28551 .
>> 
>> Summarizing that issue to bring to the attention of pypa has been on 
>> my todo backlog for a while.  This may be a cleaner case to bring to 
>> pypa with a more contemporaneous reproducer.
>> 
>> Tom
>> 
>> On Sun, Nov 23, 2025 at 7:12 AM Phil Thompson 
>> <phil at riverbankcomputing.com> wrote:
>> 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
>> 
>> 
>> --
>> Thomas Caswell
>> tcaswell at gmail.com