`monitor_dump_state` shows only one monitor despite two being added

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Upfront Information

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

Fvwm3 version (run: fvwm3 --version)

Commit b92ecb292ec639dc2701c3d172d6891417858d8a, then built as in Debian with

./autogen.sh 
./configure --verbose --disable-imlibtest --with-imlib-prefix=/no/dir --with-readline-ibrary=yes --enable-mandoc --enable-htmldoc --program-transform-name='/vwm[^3]/ s/vwm/vwm3/'

Linux distribution or BSD name/version

Debian testing with Fvwm3 built from main.

Platform (run: uname -sp)

Linux unknown

Expected Behaviour

I'm trying to understand Fvwm's monitor handling and patched it as follows:

diff --git a/libs/FScreen.c b/libs/FScreen.c
index a7742f66..38e2d7b9 100644
--- a/libs/FScreen.c
+++ b/libs/FScreen.c
@@ -626,6 +626,7 @@ out:
         */
        monitor_assign_number();
        monitor_check_primary();
+       monitor_dump_state(NULL);
        XRRFreeMonitors(rrm);
 }

Then I ensured that xrandr finds both monitors:

[~]$ xrandr --listactivemonitors
Monitors: 2
 0: +*eDP-1 1920/285x1200/190+0+0  eDP-1
 1: +DP-3-2 1920/519x1200/324+0+0  DP-3-2

In that scenario, I'd expect that the call to monitor_dump_state would list also both these monitors when I restart Fvwm3 with above changes.

Actual Behaviour

However, I get the following in my journal:

fvwm3[2467]: [1728509559.609360] FScreenInit: Using RandR 1.6
fvwm3[2467]: [1728509559.709165] scan_screens: Case 1: Add new monitors
fvwm3[2467]: [1728509559.709474] monitor_mark_new: Added new monitor: eDP-1 (0x55863a1999b0)
fvwm3[2467]: [1728509559.709580] monitor_mark_new: Added new monitor: DP-3-2 (0x55863a189760)
fvwm3[2467]: [1728509559.709861] monitor_dump_state: Monitor Debug
fvwm3[2467]: [1728509559.709874] monitor_dump_state:         number of outputs: 1
fvwm3[2467]: [1728509559.709893] monitor_dump_state:         Number:        0
fvwm3[2467]:         Name:        eDP-1
fvwm3[2467]:         Disabled:        false
fvwm3[2467]:         Is Primary:        yes
fvwm3[2467]:         Is Current:        yes
fvwm3[2467]:         Is Previous:        no
fvwm3[2467]:         Output:        66
fvwm3[2467]:         Coords:        {x: 0, y: 0, w: 1920, h: 1200}
fvwm3[2467]:         VirtScr: {
fvwm3[2467]:                 VxMax: 0, VyMax: 0, Vx: 0, Vy: 0
fvwm3[2467]:                 EdgeScrollX: 0, EdgeScrollY: 0
fvwm3[2467]:                 CurrentDesk: 0
fvwm3[2467]:                 CurrentPage: {x: 0, y: 0}
fvwm3[2467]:                 MyDisplayWidth: 1920, MyDisplayHeight: 1200
fvwm3[2467]:         }
fvwm3[2467]:         EWMH: {
fvwm3[2467]:                 BaseStrut Top:    0
fvwm3[2467]:                 BaseStrut Bottom: 0
fvwm3[2467]:                 BaseStrut Left:   0
fvwm3[2467]:                 BaseStrut Right:  0
fvwm3[2467]:         }
fvwm3[2467]:         Desktops:        no
fvwm3[2467]:         Flags:global
fvwm3[2467]: [1728509559.788909] main: Loading window states via /home/jschmidt/.fvwm/.fs-restart-sappc1:0

So monitor_add/monitor_mark_new get called on both monitors, but the resulting dump shows only one?!

Unfortunately, my gdb foo is not good enough to trace down the RB-tree ops. What I could get from gdb was that information from monitor_get_count (with the same monitor setup as shown above):

(gdb) b monitor_get_count
Breakpoint 2 at 0x5593b830a440: monitor_get_count. (2 locations)
(gdb) c
Continuing.

Breakpoint 2.2, monitor_get_count () at FScreen.c:808
808             RB_FOREACH(m, monitors, &monitor_q) {
(gdb) p monitor_q
$3 = {rbh_root = 0x5593d674a9b0}
(gdb) p monitor_q->rbh_root
$4 = (struct monitor *) 0x5593d674a9b0
(gdb) p *monitor_q->rbh_root 
$5 = {si = 0x5593d674ab00, flags = 8, emit = 4, number = 0, dx = 1, dy = 1, 
  is_prev = false, was_primary = false, Desktops = 0x5593d6754c90, ewmhc = {
    NumberOfDesktops = 0, MaxDesktops = 0, CurrentNumberOfDesktops = 1, 
    NeedsToCheckDesk = 0, BaseStrut = {left = 0, right = 0, top = 0, 
      bottom = 0}}, edge = {top = false, bottom = false, left = false, 
    right = false}, virtual_scr = {VxMax = 0, VyMax = 0, Vx = 0, Vy = 0, 
    edge_thickness = 2, last_edge_thickness = 2, EdgeScrollX = 0, 
    EdgeScrollY = 0, CurrentDesk = 0, prev_page_x = 0, prev_page_y = 0, 
    prev_desk = 0, prev_desk_and_page_desk = 0, prev_desk_and_page_page_x = 0, 
    prev_desk_and_page_page_y = 0, is_swapping = false}, PanFrameTop = {
    win = 0, isMapped = 0, command = 0x0, command_leave = 0x0}, 
  PanFrameLeft = {win = 0, isMapped = 0, command = 0x0, command_leave = 0x0}, 
  PanFrameRight = {win = 0, isMapped = 0, command = 0x0, command_leave = 0x0}, 
  PanFrameBottom = {win = 0, isMapped = 0, command = 0x0, 
    command_leave = 0x0}, pan_frames_mapped = false, entry = {rbe_left = 0x0, 
    rbe_right = 0x0, rbe_parent = 0x0, rbe_color = 0}, oentry = {
    tqe_next = 0x0, tqe_prev = 0x0}}
(gdb) d
Delete all breakpoints, watchpoints, tracepoints, and catchpoints? (y or n) y
(gdb) c

fvwmorg / fvwm3