Created attachment 160072 [details]
example source

SUMMARY
KJobPrivate has

    // eventLoopLocker prevents QCoreApplication from exiting when the last
    // window is closed until the job has finished running
    QEventLoopLocker eventLoopLocker;

The way this works is that each QEventLoopLocker has a refcount in the QCoreApplication, when the counter hits zero the application quits. That means when all kjobs are destroyed the application always quits - regardless of whether it was meant to!

I'm going to attach a trivial example.

For QGuiApplications this is additionally contingent on its quitOnLastWindowClosed property, but when that is set to false the call chain falls back into QCoreApplication and behaves exactly the same. Put another way: you cannot use KJobs and QGuiApplications that are meant **not** to quit because running out of KJobs always force quits the application.

I'm not quite sure what the fix here should be. Maybe install an eventfilter on the QCoreApplication and only install the lockers on QEvent::Quit? Alternatively we could bounce this to Qt since this behavior arguably makes QEventLoopLocker only niche-useful. Someone probably needs to track whether quit was actually called on the application though.

SOFTWARE/OS VERSIONS
Operating System: KDE neon Unstable Edition
KDE Plasma Version: 5.27.80
KDE Frameworks Version: 5.240.0
Qt Version: 6.5.1
Kernel Version: 5.19.0-42-generic (64-bit)
Graphics Platform: offscreen
Processors: 12 × AMD Ryzen 5 3600X 6-Core Processor
Memory: 31.3 GiB of RAM
Graphics Processor: AMD Radeon RX 5700 XT

ADDITIONAL INFORMATION