Crashing with QApplication Error

[ytene]

Platform/Configuration:
Mint 17.3/64-bit [clean installation] with Cinnamon Desktop

Symptoms:
From "Menu" WallCh will open, but any attempt to i.e. adjust the image refresh interval will result in an immediate app crash.

Launching WallCh from the command line identifies the possible problem:

c1@S1 ~ $ wallch
QEventLoop: Cannot be used without QApplication
QDBusConnection: system D-Bus connection created before QCoreApplication. Application may misbehave.
Floating point exception
c1@S1 ~ $ wallch --version
QEventLoop: Cannot be used without QApplication
QDBusConnection: system D-Bus connection created before QCoreApplication. Application may misbehave.
Wallch - Wallpaper Changer, Version 4.0

Checking /var/syslog provides one additional piece of information:

Dec 18 10:08:02 S1 kernel: [ 95.329564] traps: wallch[2754] trap divide error ip:458897 sp:7ffe9b3d87e0 error:0 in wallch[400000+13a000]

Observations:
The really interesting thing is that very occasionally I can get this to work [i.e. adjust the image refresh interval from 15 minutes to 5 - and when I do then wallch will continue to operate for the entire duration of the session with zero issues. Although the error message clues sort-of hint to a fundamental calculation or process error, the observed behaviour is tending much more towards a level of unreliability, as opposed to an outright failure rate. Which is very odd.

Sorry, but this takes me pretty close to the limit of my diagnostic capabilities [ I am just a numpty user, not a developer] but I am happy to check and report back any more details should you require them.

Thank you.

[Don Geddis (don-geddis)]

I can confirm the same symptoms on my system. Every time I log in, my wallch tray icon is in the menu bar, but it hasn't actually started. I open ("show") the wallch panel, click start (twice), it crashes with a floating point exception. I manually restart it from the command line, then click start (twice). It crashes, on average, 10 to 20 times in a row. And then, it a stroke of luck, one of the attempts to click start (twice) suddenly works! And everything is fine from then on. After that, I can change wallpaper directories, change the time between wallpapers, etc.

But every single time I reboot/logon again, I have to go through another 10-20 manual attempts to start wallch.

[Bob Merhebi (bobmerhebi)]

It's weird. I was just woring and sudenly I realized the wallpaper hasn't changed in days. Starting it from the terminal returns the error reported in this bug.
Moreover, the ppa for vivid fails to update.

[Jonathan Drapeau (dranon)]

If I try to start wallch from the command line, I get this error (mint 18.1) but it starts fine when auto-launching at startup but live earth and picture of the day won't refresh, connection error.

[oompi testeresse (oompi)]

The bug still exists on "Linux comp 4.13.0-38-generic #43~16.04.1-Ubuntu SMP Wed Mar 14 17:48:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux" so I don't think it's going to be fixed anymore.

As a workaround, using the command line including valid args, e.g. wallch --start WorksForMe.

In case the time-triggered pic-changer doesn't work, you can kill the two wallch processes and start it again without args, the GUI should come up then (provided it was started using args beforehand). Change the default pic-change time from 15 minutes to something else and close the GUI. Then use wallch --start.