[cuegui] Fix crash when closing preview dialog before images are ready

[ramonfigueiredo]

Related Issues

• [cuegui] Cuetopia crashes when the "Waiting for preview images" dialog is closed before images are ready #2396

Summarize your change.

• Closing the "Waiting for preview images..." dialog before the preview images were ready crashed the app with "QThread: Destroyed while thread is still running" / Aborted.
• The close handler only set the watch thread's terminate flag without waiting for the QThread to exit, so the thread (parented to the dialog) was destroyed mid-execution, which Qt treats as a fatal error.
• Fix PreviewProcessorDialog.__close to stop the thread and wait() for it to finish before the dialog is destroyed, and guard against the thread not yet existing.
• Make PreviewProcessorWatchThread.run sleep in small slices so it reacts to stop() promptly instead of freezing the GUI for up to a second, and move the timeout check before the sleep.

[coderabbitai]

📝 Walkthrough

Walkthrough

The PR fixes thread lifecycle management in the Preview widget. PreviewProcessorDialog.__close now calls stop() and wait() on the watch thread before dialog destruction, preventing Qt fatal errors. PreviewProcessorWatchThread.run replaces a single 1-second sleep with 10 iterations of 0.1-second sleeps that check the terminate flag, enabling responsive GUI shutdown.

Changes

Thread Lifecycle Management

Layer / File(s)	Summary
Safe thread shutdown with responsive reaction cuegui/cuegui/PreviewWidget.py	PreviewProcessorDialog.__close calls stop() and wait() on the watch thread before destruction. PreviewProcessorWatchThread.run checks the terminate flag in 0.1s intervals instead of blocking for 1 second, allowing responsive shutdown.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested reviewers

• DiegoTavares
• lithorus

Poem

🐰 The threads now dance in harmony,
No more fatal crashes in our GUI,
With stop() and wait(), we reign supreme,
A hundred milliseconds, a smoother dream!
Qt frowns no more when we depart.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main fix: preventing a crash when closing the preview dialog before images are ready, which directly matches the core changes made to handle thread shutdown properly.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[ramonfigueiredo]

@DiegoTavares / @lithorus
Ready for review!