Bug 439723

Summary: While printing special sample file or generating a printer preview for it the UI freezes
Product: [Applications] okular Reporter: postix <postix>
Component: printingAssignee: Okular developers <okular-devel>
Status: ASSIGNED ---    
Severity: normal CC: aacid, nate, nicolas.fella, postix
Priority: NOR    
Version First Reported In: 21.04.3   
Target Milestone: ---   
Platform: Other   
OS: Linux   
Latest Commit: Version Fixed/Implemented In:
Sentry Crash Report:
Attachments: Flamegraph for CPU1

Description postix 2021-07-10 14:41:36 UTC 
Created attachment 139981 [details]
Flamegraph for CPU1

STEPS TO REPRODUCE
1. Open https://bugs.kde.org/attachment.cgi?id=139894 in Okular
2. File -> Printer Preview
OR 
2. File -> Print

OBSERVED RESULT

Okular uses 100% of one core for several seconds and the UI freezes until the preview is finally generated.
I tried to use perf to check what it's going on, please find the flamegraph.svg attached.

It seems to run on the same thread as the UI if I am not mistaken?


SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20210704
KDE Plasma Version: 5.22.2
KDE Frameworks Version: 5.83.0
Qt Version: 5.15.2
Kernel Version: 5.13.0-1-default (64-bit)
Source: openSUSE TW repo and source build (master)
Comment 1 Nicolas Fella 2022-01-12 15:58:57 UTC 
> It seems to run on the same thread as the UI if I am not mistaken?

yes, that appears to be the case.

What might make sense is to change "Document::PrintError print(QPrinter &printer)" to something like "PrintJob print(QPrinter &printer)" where PrintJob is a (KJob derived) class that encapsulates an async print operation. 

However that touches the generator interface, which as I understand is subject to ABI constraints?
Comment 2 Albert Astals Cid 2022-01-12 18:39:04 UTC 
(In reply to Nicolas Fella from comment #1)
> However that touches the generator interface, which as I understand is
> subject to ABI constraints?

We just broke ABI so if you want to break it, now it's the time 
https://invent.kde.org/graphics/okular/-/commit/a2576dc746767f0ca0bda174c8e2b8d4817d0c2b
Comment 3 Bug Janitor Service 2022-01-13 23:03:08 UTC 
A possibly relevant merge request was started @ https://invent.kde.org/graphics/okular/-/merge_requests/540