Qt 5 & 6 problems in linux (details in the topic)

Valso

In the last few days whenever I try to insert/attach a file into any program that uses Qt5 and Qt6, the file selector window takes about a minute to appear and it's being rendered very slowly. "GTA 5 on a Pentium IV" slowly. When it finally appears, clicking anywhere on the file selector causes even more slowliness. After I double click the file that needs to be inserted/attached, a freeze follows and in about a minute or two the file appears in the program.
At first I thought it was just Telegram-Desktop (qt6) but then KolourPaint (qt5) started doing the same.
I ran each of these in terminal (Linux) and in both cases I got similar outputs.

This the telegram-desktop output:

qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "stateChanged"
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "connectivityChanged"
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "deviceTypeChanged"
qt.dbus.integration: Could not connect "org.freedesktop.NetworkManager" to "meteredChanged"
QPainter::begin: Paint device returned engine == 0, type: 2
QWidget::render: Cannot render with an inactive painter
qt.svg: Error while inflating gzip file: SVG format check failed

This is kolourpaint's output:

QPainter::begin: Paint device returned engine == 0, type: 2
QWidget::render: Cannot render with an inactive painter
qt.svg: Error while inflating gzip file: SVG format check failed
QPainter::begin: Paint device returned engine == 0, type: 2
QWidget::render: Cannot render with an inactive painter
QWidget::render: Cannot render with an inactive painter
QWidget::render: Cannot render with an inactive painter

Even Audacious got affected by this qt problem but I solved its problem by installing the GTK3 build. But telegram and kolourpaint don't have GTK3 builds, unfortunately.

I did search for these errors, but all I found was from developers having problems when they write and debug code and my case isn't about coding, so here I am asking for suggestions how to fix this.

ChrisW67

Which Linux flavour?
Have you updated, added, or removed any components in "last few days"?
Are the applications installed natively or bundled as Snap/FlatPak/AppImage?

This message:

qt.svg: Error while inflating gzip file: SVG format check failed

may indicate a corrupt file in a theme.
Do the affected applications behave differently if started with the -style fusion, or even -style windows, command line option?

Valso

@ChrisW67 Natively. I hate bundles and these particular apps don't have bundles, at least none that I could find anyway.
The distro is Arch Linux. I haven't added anything new, only updated what was already there. This morning I reinstalled Arch just for the test to see whether these apps would behave any differently on a fresh install and they didn't, so the problem isn't caused by me, it's how the packages arrive - broken.

SamiV123

@Valso

That's the state of linux for you, always broken somewhere ;-)

That being said I'm also on arch and haven't seen this (yet).

Have you check the arch forum or the wiki for any issues like this?

Have you checked that your machine has some expected state, such as it's not out of disk space? Your /tmp and /home have disk space? You have enough free memory?

I've seen weird failures on Linux when accidentally my /tmp partition had 0 space left...

The year of the Linux desktop is always 10 years from now. ;-)

Valso

@SamiV123 Free space and free memory are fine. I'm using a command which deletes all downloaded packages, after the update has been completed + I do the same thing with an alias, so free space is never an issue. Even now I have 89 GiB free space on the system SSD.
Free memory is not an issue either. Both kolourpaint and telegram start using a lot of memory when they freeze but even then the busy memory never exceeds 12 GiB and I have 31.3 GiB total (32 GB in Windows terms).

I made a video of the problem, you can see how slowly it reacts. The same thing happens with kolourpaint.
https://disk.yandex.com/i/6yaeXWmkqZXUZA

SamiV123

@Valso

Few possible ideas,

Are you always trying to access the same folder and does the folder contain a lot of files ? Most software begins to shit itself when you start doing stuff like putting 10k files in a folder...
Try opening a terminal xterm or whatever that is normally snappy and cd into the same folder and run ls there, if this janks then it's a problem with the system for sure.
Is your disk and your filesystem working as expected ? Have you checked dmesg for errors and ran fsck ?

Anyway, I don't think this is a Qt issue.

Valso

@SamiV123 Sure it isn't a qt problem. QPainter & QWidget are not part of Qt and Qt is a perfect, bug free framework, just like GNOME is a perfect and bug free desktop. (sarcasm)

Christian Ehrlicher

@Valso said in Qt 5 & 6 problems in linux (details in the topic):

QPainter & QWidget are not part of Qt

If suddenly out of nowhere errors occur in two different libs then blaming them is for sure the right thing...

JoeCFD

@Valso Pentium IV were shipped from November 20, 2000 until August 8, 2008. Is that true?

DavidFaure

For the record, the NetworkManager warnings in the initial post are harmless. I just fixed them in https://codereview.qt-project.org/c/qt/qtbase/+/527739 though.