https://bugs.kde.org/show_bug.cgi?id=475205
Bug ID: 475205
Summary: [UX/Perf] : UI freezes when handling big projects /
adding lots of clips in the resource folder
Classification: Applications
Product: kdenlive
Version: 23.08.0
Platform: Archlinux
OS: Linux
Status: REPORTED
Severity: major
Priority: NOR
Component: User Interface
Assignee: j...@kdenlive.org
Reporter: benoittarr...@hotmail.fr
Target Milestone: ---
Created attachment 162080
--> https://bugs.kde.org/attachment.cgi?id=162080&action=edit
Kdenlive starts to freeze right away (loading a big project)
SUMMARY
Kdenlive UI seems to be very tied to the underlying processes, thus making the
UI event processing loop stuck for some reasons. This happens either when :
* dropping a big folder into the resource explorer
* opening a saved project which points to a lot of resources.
In my context, I am working on a project where I have around 1500 items (video
and pictures) for a total of around 33 GB.
That's a lot of files, and kdenlive (or mlt!) takes sometimes close to 10
minutes scanning all of them, making the UI totally unresponsive. This happens
on every load as well, so it seems caching is not sufficient (by the way, I'm
having a lot of logs saying "GOT THUMBNAIL : -1 x -1" ; don't know what that
means exactly but it seems that the cache contains thumbnails at least.
=> This is an I/O bound issue, Kdenlive lacks asynchronicity when it comes to
opening files/and performing preprocessing tasks on them (parsing/loading
content, computing thumbnails, etc.)
STEPS TO REPRODUCE
1. Open a new project
2. Drop a big folder with few tens of clips in the resource explorer
3. Alternative : save a big project and reopen it later on, file indexing seems
to be taking very long as well and if the amount of files is big, it takes
forever (especially if data is stored on a not-brand-new HDD).
OBSERVED RESULT
The loading dialog appears (and is more or less frozen), most of the times the
Desktop manager shows and asks if you want to kill the process (because Qt
needs to ping the Destkop manager's watchdog periodically, otherwise it's
considered a zombie process)
Then wait. Eventually Kdenlive will get to the point where it finishes loading,
or at least gets out of the work intensive loop it's stuck in and the little
"xxx tasks" counter increases suddenly, and the UI comes back to life.
EXPECTED RESULT
The UI should remain responsive at all times, and the user shall be able to
cancel the loading process if he/she needs to.
Like "Whoops, I dropped the wrong folder ! I do I do know to stop it from
loading this 4000 files rush folder ??". For now you need to kill the process,
or make one good cup of coffee :)
SOFTWARE/OS VERSIONS
Linux/KDE Plasma: Linux arch-linux 6.1.55-1-lts #1 SMP PREEMPT_DYNAMIC ///
Gnome 44.5 / X11
Qt Version: Qt 5.15.x
ADDITIONAL INFORMATION
> /!\ I haven't taken the time to read the source code yet, maybe what I'm
> saying here is off (and in such a case I apologize), but I'm trying to lay
> out some ideas here
My gut feeling is that we need to defer (and push in background loading tasks)
files loading as much as we can and prioritize the loading order so that the
end user can start working as soon as possible !
* A simple stat should be enough to check if the file is reachable and valid
* All I/O bound operations need to be as asynchronous as possible (maybe using
the std::future for ease of use, or put in a background thread that'll wait the
I/O and move on to the next one)
* Thumbnails shall be computed only for the visible par of the viewport in the
resources folder and cached for later reuse, I believe the caching is already
written, but I think thumbnail generation really takes too much time (again, my
gut feeling; I might really well be wrong)
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