Severe thread leak (NLWP growth) when adjusting blur or opacity in Fill and Stroke dialog

Vit
2026-04-02T15:44:55Z

#### Summary:
Adjusting the blur or opacity sliders in the Fill and Stroke dialog causes a rapid increase in the Number of Light Weight Processes (NLWP/threads) for the Inkscape process. This leads to severe system performance degradation and application unresponsiveness.

#### Steps to reproduce:
- Open a terminal window.
- Run the following command to monitor thread count: `watch -n 1 'ps -eLo pid,comm,nlwp --sort=-nlwp | head -n 2'`
- Launch Inkscape.
- Create a new blank document.
- Draw a rectangle using the rectangle tool.
- Open the Fill and Stroke dialog.
- Adjust the Blur slider or the Opacity slider: click and drag the "Blur" slider in the "Fill" tab (do not just type a value, move the slider with the mouse). Alternatively, click and drag the "Opacity" slider.
- Observe the NLWP count in the terminal window while adjusting the parameters.

#### What happened?
Upon changing the blur or opacity values, the NLWP count for the Inkscape process increases rapidly, approximately 3000 to 5000 threads per second. The count continues to rise until it reaches approximately 65,000 threads. This excessive thread creation causes the system to lag significantly.

#### What should have happened?
The NLWP count should remain stable during normal operation. Adjusting visual parameters such as blur or opacity should not result in the creation of thousands of threads or cause system-wide performance issues.

Sample attachments:
No specific file attachment is required. The issue reproduces consistently on a new blank document with a basic shape.

#### Version info

```
Inkscape 1.4.3 (fcd0343856, 2026-01-01)

Compile (Run)
GLib version: 2.72.4
GTK version: 3.24.33 (3.24.33)
glibmm version: 2.66.2
gtkmm version: 3.24.5
libxml2 version: 2.9.13
libxslt version: 1.1.34
Cairo version: 1.16.0 (1.16.0)
Pango version: 1.50.6 (1.50.6)
HarfBuzz version: 2.7.4 (2.7.4)

OS version: Ubuntu Core 22

Installation method: Snap
Path: /snap/bin/inkscape
Kernel: Linux s 6.17.0-19-generic #19~24.04.2-Ubuntu SMP PREEMPT_DYNAMIC Fri Mar 6 23:08:46 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
```