[kde] [Bug 456696] New: "QSocketNotifier: Can only be used with threads started with QThread" everywhere

[Russell Haley]

https://bugs.kde.org/show_bug.cgi?id=456696

            Bug ID: 456696
           Summary: "QSocketNotifier: Can only be used with threads
                    started with QThread" everywhere
           Product: kde
           Version: unspecified
          Platform: Fedora RPMs
                OS: Linux
            Status: REPORTED
          Severity: minor
          Priority: NOR
         Component: general
          Assignee: unassigned-bugs at kde.org
          Reporter: yumpusamongus+kde at gmail.com
  Target Milestone: ---

Created attachment 150603
  --> https://bugs.kde.org/attachment.cgi?id=150603&action=edit
Fedora 36 upgrade transaction

Many things on my system recently started printing this to stderr.  It's mostly
just annoying, but it does get into the stdout of `kscreen-console json`  and
make the json invalid, and having this warning showing up in my consoles all
the time feels a bit dodgy.


STEPS TO REPRODUCE

1. `kioclient5 stat`

... is the shortest command I know that prints the error and exits immediately,
but it's much more widespread.

OBSERVED RESULT

    QSocketNotifier: Can only be used with threads started with QThread
    kioclient5: Syntax error, not enough arguments

EXPECTED RESULT

    kioclient5: Syntax error, not enough arguments

SOFTWARE/OS VERSIONS

Linux/KDE Plasma: Fedora 36
KDE Plasma Version: 5.25.2
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.3

ADDITIONAL INFORMATION

This shows how many times the message has been logged by various programs since
boot:

    journalctl -b --output cat --output-fields=_EXE MESSAGE='QSocketNotifier:
Can only be used with threads started with QThread' | sort | uniq -c | sort
-nk1,1

On my machine, it prints:

      1 /usr/bin/dolphin
      1 /usr/bin/korganizer
      1 /usr/bin/kstart
      1 /usr/bin/kwrite
      1 /usr/bin/okteta
      1 /usr/bin/plasma-discover
      1 /usr/libexec/ksmserver-logout-greeter
      2 /usr/bin/akonadi_archivemail_agent
      2 /usr/bin/akonadi_birthdays_resource
      2 /usr/bin/akonadi_control
      2 /usr/bin/akonadi_followupreminder_agent
      2 /usr/bin/akonadi_indexing_agent
      2 /usr/bin/akonadi_maildispatcher_agent
      2 /usr/bin/akonadi_mailfilter_agent
      2 /usr/bin/akonadi_mailmerge_agent
      2 /usr/bin/akonadi_migration_agent
      2 /usr/bin/akonadi_newmailnotifier_agent
      2 /usr/bin/akonadi_sendlater_agent
      2 /usr/bin/akonadi_unifiedmailbox_agent
      2 /usr/bin/akonadi_vcard_resource
      2 /usr/bin/corectrl
      2 /usr/bin/kalendarac
      2 /usr/bin/kcminit_startup
      2 /usr/bin/kded5
      2 /usr/bin/ksplashqml
      2 /usr/bin/kwalletd5
      2 /usr/bin/plasmashell
      2 /usr/libexec/baloorunner
      2 /usr/libexec/DiscoverNotifier
      2 /usr/libexec/kactivitymanagerd
      2 /usr/libexec/kdeconnectd
      2 /usr/libexec/kf5/polkit-kde-authentication-agent-1
      2 /usr/libexec/org_kde_powerdevil
      2 /usr/libexec/xdg-desktop-portal-kde
      4 /usr/bin/akonadi_akonotes_resource
      4 /usr/bin/akonadi_contacts_resource
      4 /usr/bin/akonadi_ical_resource
      4 /usr/bin/akonadi_maildir_resource
      4 /usr/bin/systemsettings
     36 /usr/bin/konsole
     39 /usr/libexec/kscreenlocker_greet

According to `sudo rg --one-file-system -Suu "Can only be used with threads"
--binary /usr`, the message probably comes from
/usr/lib64/libQt5Core.so.5.15.3, which the top culprits link against according
to `ldd`, and which is provided by the qt5-qtbase package.

According to `dnf history`, this package was updated from version 5.15.2-30 to
version 5.15.3-1 as part of the Fedora 35->36 upgrade on 2022-05-12.  I have
attached the `dnf history info` from that transaction.

Oddly, the logs show 59 occurances of the message from 2022-03-29, when the
installed qt5-qtbase version was 5.15.2, but then it didn't appear again until
many boots later on 2022-05-16, which was the SECOND (wat?) boot and login
session after the Fedora 35->36 upgrade, with no intervening dnf transactions.
Unfortunately, I have no logs from before 2022-03-29, because
plasma-systemmonitor had some kind of fit and spammed hundreds of messages per
second, which flushed the journal from before that date.

I don't know whether this is a problem with libQt or with the use of it.

This seems similar to bug 418402, but it has a much wider blast radius and
seems to have started with a different version of qt5-qtbase.

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