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How to track down a bug w/ PyGTK3 which freezes the UI?




Hi,

I'm using PyGTK3 [python3.7, Debian 9.7 @ x86_64, Gtk 3.22.11] for an embedded UI [X11, Xfce4, kiosk mode].

I noticed that after a while, the UI "freezes": the UI items are not repainted anymore, whatever Gtk calls are invoked.

I initially thought the main loop was stuck for some reason, but it is definitely not: execution goes on, application threads and UI thread keep logging traces. I've also added a timer (GLib.timeout_add) which keeps being called at the defined pace.

I double-checked that all calls made from the application threads to Gtk loop directly go through GLib.idle_add; all events received from Gtk are pushed into an event queue that the application thread manages, to avoid any long calls that could be made from the main context.

Any hint on how to debug this kind of issue would be appreciated, as I'm out of ideas. GDB is available on the test platform, although I'm not sure how to track this issue from there.

Additional details about this problem:

UI items include several text labels, a progress bar, and two basic drawing areas, all contained in a page of a notebook. The app is running in full screen mode [800x480].

I run the app with some kind of auto-test mode, to run the same sequence again and again until it freezes, without any user input - nor any input event.

When it freezes, the application does not crash, the CPUs show no noticeable load when the UI freezes.

The UI freezes "randomly", from 5 to 100 cycles. Each cycle last ~ 4 seconds. A cycle makes less than a hundred calls to Gtk API.

The UI provides a modal dialog to quit the app, which can be kicked in from the main menu bar. When the UI is frozen, e.g. many calls to change the content of the text label, the progress bar fraction value, etc. have not been serviced, the dialog nevertheless shows up. Sometimes, its contents is painted successfully, sometimes only the dialog frame (inc. buttons) is displayed along with its title text, while the dialog content area is not (re)painted...

Using the GTK+ inspector, I can see that the text labels, the progress bar fraction, etc. are actually updated whereas the UI does not refresh their contents. However, the GdkFrameClockIdle counters *all* stop as the same time the UI is not updated anymore.

What could cause this kind of trouble, where the UI is not refreshed anymore, but main context seems to be up and running?

Thanks,
Manu.
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