FvwmEvent event new_desk gets triggered multiple times in multi-monitor shared setup

[NsCDE]

• Fvwm3 version (run: fvwm3 --version)

fvwm3 1.0.5 (1.0.4-116-g8342d9dc)
with support for: ReadLine, XPM, PNG, SVG, Shape, XShm, SM, Bidi text, XRandR, XRender, XCursor, XFT, NLS

• Linux distribution or BSD name/version

Debian 11

• Platform

Linux x86_64

Expected Behaviour

In four monitor setup, and DesktopConfiguration is set to "shared", there should be only one trigger for the new_desk event. However ...

Actual Behaviour

... new_desk event is triggered 7-9 times. Looks like as fast as it can until desk is changed. Reducing number of monitors to two, also reduces this triggering to 2-4.

Enabling logging

Function which is defined for new_desk event - if we put some Echo at the beginning (2 monitors):

[1645631581.505294] CMD_Echo: DESK IS: 2
[1645631581.615735] CMD_Echo: DESK IS: 2
[1645631581.633214] CMD_Echo: DESK IS: 2
[1645631581.654741] CMD_Echo: DESK IS: 2
[1645631583.051600] CMD_Echo: DESK IS: 3
[1645631583.087933] CMD_Echo: DESK IS: 3

Steps to Reproduce

• Enable FvwmEvent module and configure new_desk to run some verbose/visible function

• Configure virtual (or real) environment with 4 monitors.

• Configure FVWM with DesktopConfiguration shared

• Enable monitors (example): xrandr --output Virtual-1 --mode 1400x1050 --primary --output Virtual-2 --mode 1400x1050 --right-of Virtual-1 --output Virtual-3 --mode 1400x1050 --below Virtual-1 --output Virtual-4 --mode 1400x1050 --below Virtual-2

• Restart FVWM (FvwmMFL must be enabled in config): FvwmCommand Restart

• Observe ~/.xsession-errors ~/fvwm.log or equivalent for echo from your function which is run by FvwmEvent on new_desk event

• Does the problem also happen with Fvwm2?

N/A

Does Fvwm3 crash?

No.

Extra Information

This weird event behaviour may be similar to disfuctional monitor_focus in #604

[ThomasAdam]

Hi @NsCDE

Please can you try the ta/fix-655 branch to see if this resolves the reported problem?

Thanks!

[NsCDE]

Hi Thomas,

I'm back from vacation and had a bunch of work to do. I see you merged this into the master, so I just compiled master and tried.

I'm afraid I have to tell you it is still triggering multiple times. That is, NsCDE function f_ChangeDesk called from new_desk produces multiple "CMD_Echo: DESK IS: X" if I put "Echo DESK IS $[desk.n]" in that function.

P. S.
I saw you produced couple more fixes, I will test this when I catch some free time.

[NsCDE]

Fvwm Event conf:
https://github.com/NsCDE/NsCDE/blob/master/data/fvwm/Event.fvwmconf

Function of new_desk (About line 1546 f_ChangeDesk)
https://github.com/NsCDE/NsCDE/blob/master/data/fvwm/Functions.fvwmconf.in
First line of function in my tests was added: "+ I Echo DESK IS: $[desk.n]"

[ThomasAdam]

Hi @NsCDE

Hopefully this is working correctly now. I think I've made this function the way it should with 'shared', and also fixed the same type of problem with 'global' wherein, that would cause N number of NEW_DESK events per N monitors detected.

Try the ta/fix-655 branch, and let me know how you get on.

[NsCDE]

Sorry to tell you, but it is still hitting 3 times:

[1663437479.245486] CMD_Echo: DESK IS: 2
[1663437479.321148] CMD_Echo: DESK IS: 2
[1663437479.338521] CMD_Echo: DESK IS: 2

But only when it needs to move/flip desks between monitors, that is, when I choose on one monitor desk that is active on another monitor. For desks which are invisible (2 monitors, 4 desks) this is called only once.

[ThomasAdam]

Hmm.

Here's what I've been using to test this with. Don't worry so much about the bogus values which get printed:

DestroyModuleConfig FET: *
*FET: PassID
*FET: Cmd
*FET: new_desk fnd

DestroyFunc fnd
AddToFunc   fnd
+ I Echo "[$0 - $1]: MONITOR: $[w.screen]: DESK: $[w.desk]"

DesktopConfiguration shared
KillModule FvwmEvent FET
Module FvwmEvent FET

For me, I get the expected number of events.

[ThomasAdam]

As seen here:

[1663438508.324695] CMD_GotoDesk: Swapping HDMI-1/1 with DP-1-2/0
[1663438508.324993] MapDesk: '[0x2e0001e] xterm (3)' is on [DP-1-2 (0)], and should be on: [HDMI-1 (0)]
[1663438508.327464] MapDesk: '[0x2c0001e] FvwmPrompt (1)' is on [DP-1-2 (0)], and should be on: [HDMI-1 (0)]
[1663438508.329924] MapDesk: '[0x1c00002] Inbox - thomas@xteddy.org - xteddy Mail - Google Chrome (1)' is on [DP-1-2 (0)], and should be on: [HDMI-1 (0)]
[1663438508.332384] MapDesk: '[0x1a0001e] xterm (2)' is on [DP-1-2 (0)], and should be on: [HDMI-1 (0)]
[1663438508.334736] MapDesk: '[0x180001e] xterm (1)' is on [DP-1-2 (0)], and should be on: [HDMI-1 (0)]
[1663438508.339727] MapDesk: '[0x1c00004] kivikakk/libpcre.zig: Zig bindings to libpcre - Google Chrome (1)' is on [HDMI-1 (1)], and should be on: [DP-1-2 (1)]
[1663438508.342325] MapDesk: '[0x1c00005] Prize crossword No 28,865 | Crosswords | The Guardian - Google Chrome (1)' is on [HDMI-1 (1)], and should be on: [DP-1-2 (1)]
[1663438508.343123] MapDesk: '[0x1c00006] Cryptic crossword No 28,864 | Crosswords | The Guardian - Google Chrome (1)' is on [HDMI-1 (1)], and should be on: [DP-1-2 (1)]
[1663438508.352101] CMD_Echo: "[0 - ]: MONITOR: $[w.screen]: DESK: $[w.desk]"
[1663438508.356667] CMD_Echo: "[1 - ]: MONITOR: $[w.screen]: DESK: $[w.desk]"

Note the two CMD_Echo lines coming from the above config -- that's the only two from the respective monitors in question.

[NsCDE]

As we noted on IRC, GotoDeskAndPage is currently behaving differently than GotoDesk.

[ThomasAdam]

Branch updated -- please retest when you've time.

[NsCDE]

Hi @ThomasAdam

Now it works ok for flipping desks, that is (in two monitors scenario) when from one visible I try to get to another visible. They will be flipped and new_desk triggered twice. However, when going to some of the desks which were not presented on the monitors, new_desk event function is not triggered at all now ... for example, if on Virtual-0 there is desk 0, and on Virtual-1 desk 1, with pointer on Virtual-0 calling GotoDesk 2 will switch there, but new_desk will not be triggered, which is not the case with GotoDesk 1 which will trigger new_desk twice as (probably?) expected.

[NsCDE]

@ThomasAdam The last commit in ta/fix-655 works!

Just some point about design here:

When desks are flipped, new_desk is called for every monitor. While this may have a sense, on the other hand it can execute user's things from FvwmEvent multiple times, which may cause unwanted behaviour. In combination with some background root setter, it can impact performance while doing unnecessary same thing x. Should maybe some desk_changed new event be introduced here, or what? Maybe there is some reliable way for function called from new_desk to detect this in reliable way and adapt, but currently I cannot imagine such workaround, except some loosy schedule/deschedule or infostore "semaphors", which is also non-reliable in case of fast switching.

[ThomasAdam]

Hi @NsCDE

No... if desks are moved between monitors, only those desks which have moved are triggered via an event. You shouldn't be seeing events for desks which are not impacted by this.

As for a new event -- maybe I'll add that in the future. But for now, you'll have to track this manually.

[NsCDE]

Hi @ThomasAdam

I'm not seeing events for non-impacted desks, but events for imacted deskS - plural. Which means, the more monitors, more new_desk events for one GotoDesk if that includes flipping.

Ok, I will try to hande it, but I couldn't think of anything smarter than escaping function called by new_desk for amount of time where inforstore variable is set and removed with schedule. This is loosy and error prone as it best. :-\