Desktop: Fix #1790: Stop print command from resetting theme

[aerotog]

Fixes #1790.

This solution uses a simple print flag to reduce the chance of triggering the race condition. It's not as foolproof as an async lock, but I cannot reproduce the bug with the change added, and this check is much faster than a lock would be.

[tessus]

I did some testing with your code and it happened to me that after pressing ctrl+p rapidly a few times the print dialog stopped working. So even after pressing ctrl+p once, no print dialog shows up.

Update: Also, the theme still switches to light when printing, although it switches back right after.

[aerotog]

the theme still switches to light when printing

My understanding of the expected behavior is that the Light theme is enabled while printing and then should return back to the original configured theme.

pressing ctrl+p rapidly a few times the print dialog stopped working

That also happens in master. I believe that is a related but different bug from the theme resetting. In my testing, my change doesn't seem to make that behavior worse.

I'll take a look at the prompt being disabled, but I have a feeling that will be harder to fix.

[aerotog]

I've tried a few strategies to avoid the disabling of the print prompt but haven't had any success. The primary strategy was adding a timeout to my new isPrinting_ flag but it didn't help.

Like I said before, the temporary disabling of the print prompt exists in master and my change doesn't seem to make it any worse, so I don't think it should be considered a blocker for merging the theme reset fix.

If we decide not to take the current theme reset fix, I suggest re-purposing the original issue to address both the temporary prompt being disabled and the theme resetting.

[laurent22]

Thanks for the PR @aerotog, it indeed fixes this particular bug. For the other issue, we might need a different fix.