What is XCB Error Code 3?

Question

Checking journalctl /usr/bin/sway I see lots of errors like this

[xwayland/xwm.c:1286] xcb error: op 18:0, code 3, sequence 42593, value 4194450

What do they mean, is there any reason for concern there?

Answer 1

Not familiar with sway at all but I recently started using the xcb library (switched from xlib) and I was specifically looking for what "code 3" means, as a start to handle errors properly. Turns out, "code 3" means that the error is just a bad window - see /usr/include/xcb/xproto.h, line 1274:

#define XCB_WINDOW 3

Sway tried to perform an operation, specifically operation 18, the change of a window property (as seen on op 18:0 - as I understand it, the format is "major code:minor code"), and it failed. See /usr/include/xcb/xproto.h line 1932:

#define XCB_CHANGE_PROPERTY 18

As a programmer, I'd make great use of an error like that.

As for concerns, such an error is not that big of a problem but it is still an error, so it should be fixed. There are 17 different error codes so a bad window is probably not the only problem you see. The sequence and value numbers should not be of any particular use, they are not constants.

Here is a great site with easy access to information such as this. It has a glossary of functions for the xlib library and their respective potential errors. If you want to know more, you're gonna have to dive into the xcb and xlib header files in /usr/include/X11 and /usr/include/xcb.