new_desk from FvwmEvent rapidly fires/executes causing mouse cursor flicker and other side effects

[dumblob]

Thanks for reporting your bug here! The following template will help with
giving as much information as possible so that it's easier to diagnose and
fix.

Upfront Information

Please provide the following information by running the command and providing
the output.

• Fvwm3 version (run: fvwm3 --version)
  fvwm3 1.1.5 (1.1.4-7-ga8d2bfbff)
  with support for: XPM, PNG, SVG, Shape, XShm, SM, Bidi text, XRandR, XRender, XCursor, XFT, XFixes, NLS

• Linux distribution or BSD name/version
  Arch Linux

• Platform (run: uname -sp)
  Linux abc 6.12.63-1-cachyos-lts Create fvwm.da.po #1 SMP PREEMPT_DYNAMIC Fri, 02 Jan 2026 23:51:56 +0000 x86_64 GNU/Linux

Expected Behaviour

What were you trying to do? Please explain the problem.

DestroyModuleConfig Pages0Events: *
*Pages0Events: Cmd
*Pages0Events: new_page MyFunc
KillModule FvwmEvent Pages0Events
Module FvwmEvent Pages0Events

This causes continuous endless massively rapid fire of MyFunc right after FVWM starts (i.e. without switching pages at all!). Switching pages does not have any effect (is undistinguishable from the endless event fire).

Actual Behaviour

What should have happened, but didn't?

MyFunc should fire only when I switch pages as it used to be with 1.1.0.r71.gc71b01711 version I have been using so far.

Enabling logging

fvwm3 has a means of logging what it's doing. Enabling this when
reproducing the issue might help. To do this, either change the means fvwm3
is started by adding -v as in:

fvwm3 -v

or, once fvwm3 has loaded, send SIGUSR2 as in:

pkill -USR2 fvwm3

The resulting logfile can be found in $HOME/.fvwm/fvwm3-output.log

Steps to Reproduce

How can the problem be reproduced? For this, the following is helpful:

See above.

• Reduce the problem to the smallest fvwm configuration example (where
  possible). Start with a blank config file (fvwm3 -f/dev/null) and go from
  there.

• Does the problem also happen with Fvwm2?

No

Include your configuration with this issue.

Does Fvwm3 crash?

If fvwm3 crashes then check your system for a corefile. This is platform
dependant, however, check if:

• corefiles are enabled (ulimit -c)
• A corefile might be in $HOME or /tmp/.
• If you're using Linux (with systemd), check coredumpctl list.
  coredumpctl may need installing separately.

If you find a corefile, install gdb and run:

gdb /path/to/fvwm3 /path/to/corefile

If you're using coredumpctl then use:

coredumpctl debug

Then from within the (gdb) prompt, issue:

bt full

... and include the output here.

Extra Information

• Anything else we should know?

• Feel free to take a screen capture or video and upload to this issue if you
  feel it would help.

• Attach $HOME/.fvwm/fvwm3-output.log from the step above.

[ThomasAdam]

It'll be due to the number of packets that are now being generated -- it will be slightly more noticeable at startup, and arguably too chatting thereafter.

Could you do some debugging using FvwmMFL and subscribing to things like the new_desk event?

Something like:

printf 'set new_desk\n' | nc -U $FVWMMFL_SOCKET

You'll need nc from OpenBSD to be able to use it against a UDS.

[dumblob]

Wow, thanks for the prompt response!

I never used FvwmMFL, so I blindly ran your command and then started switching pages using a keyboard shortcut. I do not see anything suspicious here. The following listing took about 10 seconds to gather. But the mouse cursor blinks frantically and my "FvwmEvent function" is firing rapidly (I simply PipeRead an echo to stderr in each function run and get those hundreds lines of the echoed text).

$ printf 'set new_desk\n' | nc -U $FVWMMFL_SOCKET
{"connection_profile":{"version":"1.1.5","version_info":"1.1.4-7-ga8d2bfbff"}}
{"enter_window":{"window":"0x2600003"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x180000f"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x2600003"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x2600003"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x180000f"}}
{"enter_window":{"window":"0x3200012"}}
{"enter_window":{"window":"0x180000f"}}
{"enter_window":{"window":"0x3000012"}}
{"enter_window":{"window":"0x3000012"}}

(you can see different windows are getting focus when switching pages and focusing the corresponding window)

[ThomasAdam]

Hi @dumblob

It might not be the new_desk event, it could be anything, I suppose.

I'll try and reproduce it if you're able to give me some specific instructions on how to do so?

Incidentally, you shouldn't be seeing those enter_window events without first calling set enter_window. This is fixed via PR #1277

[dumblob]

Let me update to the newest revision and prep a minimal reproducer config for you.

[ThomasAdam]

Let me update to the newest revision and prep a minimal reproducer config for you.

Thanks, @dumblob -- I've also just merged the aforementioned PR, so if you "git pull" from main and try again, that'll reduce some of the noise.

[dumblob]

Here the reproducer (fvwm3 -f flicker-config.conf):

Colorset 10 VGradient 64 2 #707070 50 #000000 50 #707070, \
	fg #b9b9b9, bg #ff0000, hi #a0a0a0, sh #a0a0a0, NoShape

Style "Pages0" !Title, WindowListSkip, !CirculateHit, \
   !CirculateHitIcon, !CirculateHitShaded, StartsRaised, \
   FixedSize, FixedPosition, PositionPlacement 50-50w 40-50w, \
   StickyAcrossPages, NeverFocus, Borders, BorderWidth 1, \
   !Handles, BorderColorset 12, MinWindowSize 0 0, MaxWindowSize 0 0

DestroyModuleConfig Pages0Events: *
*Pages0Events: Cmd

*Pages0Events: new_page MyFunc

KillModule FvwmEvent Pages0Events
Module FvwmEvent Pages0Events

SetEnv schedule_last_pages0 0

DestroyFunc MyFunc
AddToFunc   MyFunc
+ I PipeRead "echo MyFunc enter >&2"
# latest call wins
+ I Deschedule $[schedule_last_pages0]
+ I KillModule FvwmButtons Pages0
+ I DestroyModuleConfig Pages0: *
+ I *Pages0: Colorset 10
+ I *Pages0: Rows 1
+ I *Pages0: (1x1, Frame 0, Title ABC)
+ I Module FvwmButtons -g 400x200+0+0 Pages0
# show Pages0 for only half a second
+ I Schedule 500 Function KillPages0
+ I SetEnv schedule_last_pages0 $[schedule.last]

DestroyFunc KillPages0
AddToFunc   KillPages0
+ I PipeRead "echo KillPages0 enter >&2"
+ I KillModule FvwmButtons Pages0

# switch pages
Key Left  A M GotoPage wrapx -1p 0p
Key Right A M GotoPage wrapx +1p 0p

# add page right of current
Key Up A M AddPage

DestroyFunc AddPage
AddToFunc   AddPage
# move all windows to the right
+ I PipeRead \
 'echo DesktopSize $(( $[desk.pagesx] +1 ))x$[desk.pagesy]; \
  i=$[desk.pagesx]; \
  while [ ${i} -gt $[page.nx] ]; do \
    printf "%s\\n%s\\n" \
        "GotoPage ${i} 0p" \
        "All (CurrentGlobalPage, AnyScreen, AcceptsFocus) MoveToPage +1p 0p"; \
    i=$(( i -1 )); \
  done'

(yeah, adding pages is a bit fancy 😉 )

[dumblob]

Btw. any plans adding GotoPage to the fvwm manual?

[ThomasAdam]

Btw. any plans adding GotoPage to the fvwm manual?

Hmm? What is lacking? There's an entry for it, see man fvwm3all.

[ThomasAdam]

Here the reproducer (fvwm3 -f flicker-config.conf)

Thanks, @dumblob -- I think I see the problem before even running this... umm, config. As you say though, "adding pages is a bit fancy" -- or as I like to say, "Yes, @dumblob, there's room for improvement". I'll try and give you a "better written" version of what you've provided, as I'm going along.

You may have to wait a while, apologies... Feel free to chase me if you don't hear from me in, say, four weeks. Best bet is to nudge me in the #fvwm channel on IRC (username: thomas_adam).

[dumblob]

You got me! I thought the fancy stuff would not distract you. My bad.

Anyway, the issue is of course unrelated to the fancy stuff - use this config with fixed # of pages:

Colorset 10 VGradient 64 2 #707070 50 #000000 50 #707070, \
	fg #b9b9b9, bg #ff0000, hi #a0a0a0, sh #a0a0a0, NoShape

Style "Pages0" !Title, WindowListSkip, !CirculateHit, \
   !CirculateHitIcon, !CirculateHitShaded, StartsRaised, \
   FixedSize, FixedPosition, PositionPlacement 50-50w 40-50w, \
   StickyAcrossPages, NeverFocus, Borders, BorderWidth 1, \
   !Handles, BorderColorset 12, MinWindowSize 0 0, MaxWindowSize 0 0

DestroyModuleConfig Pages0Events: *
*Pages0Events: Cmd

*Pages0Events: new_page MyFunc

KillModule FvwmEvent Pages0Events
Module FvwmEvent Pages0Events

SetEnv schedule_last_pages0 0

DestroyFunc MyFunc
AddToFunc   MyFunc
+ I PipeRead "echo MyFunc enter >&2"
# latest call wins
+ I Deschedule $[schedule_last_pages0]
+ I KillModule FvwmButtons Pages0
+ I DestroyModuleConfig Pages0: *
+ I *Pages0: Colorset 10
+ I *Pages0: Rows 1
+ I *Pages0: (1x1, Frame 0, Title ABC)
+ I Module FvwmButtons -g 400x200+0+0 Pages0
# show Pages0 for only half a second
+ I Schedule 500 Function KillPages0
+ I SetEnv schedule_last_pages0 $[schedule.last]

DestroyFunc KillPages0
AddToFunc   KillPages0
+ I PipeRead "echo KillPages0 enter >&2"
+ I KillModule FvwmButtons Pages0

# switch pages (this starts the flicker)
Key Left  A M GotoPage wrapx -1p 0p
Key Right A M GotoPage wrapx +1p 0p

DesktopSize 3x1

(I added the comment "this starts the flicker" for convenience)

Could you please confirm you can reproduce it on your end?