Sketcher: Possible crash when closing application after creating a sketch

[wwmayer]

Is there an existing issue for this?

• I have searched the existing issues

Problem description

Steps to reproduce:

1. Create sketch
2. Draw any curve element
3. Close sketcher and document
4. Exit application
5. Crash

The crash won't be notified in the vast majority of cases but nevertheless the bug is there. The crash may only be observed when building FreeCAD with the address sanitizer option.

The problem is introduced with this commit 89bf7f3
The change adds the new class CurveConverter that attaches itself to a parameter group and in its destructor it detaches itself again.

Now the problem is that a static instance is created in DrawSketchHandler::drawEdit. The point with static objects is that they will be freed after the main() function has been exited. So, at this point the Application object has been deleted.
Now the attempt to access the parameter manger inside the destructor of CurveConverter is already undefined behaviour.

Full version info

OS: Ubuntu 22.04.4 LTS (XFCE/xubuntu)
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.36963 +6 (Git)
Build type: debug
Branch: fix_new_start_page
Hash: 54f6d0083328641ac7d5a85697c5851759ccddb1
Python 3.10.12, Qt 5.15.3, Coin 4.0.0, Vtk 7.1.1, OCC 7.5.1
Locale: German/Germany (de_DE)

Subproject(s) affected?

Sketcher

Anything else?

When looking at the code base then the only instance of CurveConverter is inside DrawSketchHandler::drawEdit. So, a fix for the problem is very easy: remove the code inside the destructor and add maybe a comment.

Code of Conduct

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[wwmayer]

#13625