Python GUIs: Fixing Crashes When Using NumPy Arrays with QImage in Qt Threads — How to safely pass image data between threads when streaming video or updating displays

The useful part

I'm using a threaded runner to stream a live video feed by converting a NumPy array to a QImage, then to a QPixmap, and displaying it on a QLabel. I'm frequently encountering crashes when the label is resized too quickly or the scroll area is scrolled. Could this be a problem with the QImage memory buffer getting cleared before the QPixmap can update?

How it works

• This is a common problem when working with NumPy arrays and QImage across threads.
• If the NumPy array is modified or goes out of scope in the worker thread while the GUI thread is still using the QImage to paint, the memory that QImage is pointing to may no longer be valid.
• Instead it holds a reference to the original memory buffer provided by the NumPy array.
• The result is a segfault or (worse) a silent crash without any information about what has happened.
• This is especially likely when frames are arriving quickly (as with a live video feed) and the GUI is being redr...

Example or evidence

• Is this fixable, or is it a fundamental issue with threads in Python/Qt?