Zellij server crashes when killing X session

[raphCode]

The zellij server crashes for me when the zellij session was startet from inside X and the X server is killed.

Reproduction:
The optional steps do not influence whether the crash happens.

1. Start X and a terminal emulator (I used alacritty)
2. from the terminal emulator, run zellij
3. (optional:) Detach from the session or close the terminal emulator
4. (optional:) Login to a framebuffer console (e.g. Ctrl + Alt + F2) and attach to session zellij attach
5. kill X server, I did sudo systemctl restart lightdm to restart my display manager
6. zellij session crashes

Originating Thread(s):
1. ipc_server: AttachClient
2. screen_thread: AddClient
3. plugin_thread: Update
4. screen_thread: Render
5. ipc_server: Render

Error: thread 'router' panicked at 'called `Result::unwrap()` on an `Err` value: Io(Error { kind: UnexpectedEof, message: "failed to fill whole buffer" })': /build/zellij/src/zellij-0.24.0/zellij-utils/src/ipc.rs:168

The crash does not happen when:

• zellij session was initiated from a framebuffer console (does not crash even if attached to an X terminal)
• the X session is exited gracefully by logging out (does not crash even if logging in again and killing X)

Version information
zellij --version: 0.24.0
uname -av: Linux 5.15.12-arch1-1 #1 SMP PREEMPT Wed, 29 Dec 2021 12:04:56 +0000 x86_64 GNU/Linux

[AutumnMeowMeow]

The error doesn't look like a signals thing, but on the off chance zellij is getting the signal that killed the X server, maybe 'setsid' could be part of a solution. Some programs (e.g. 'script' grrr) send their kill to the entire process group.

[raphCode]

Mhh, systemd seems to kill all processes in the control group when restarting services:
https://stackoverflow.com/questions/40898077/systemd-systemctl-stop-aggressively-kills-subprocesses
Also man systemd.kill

But from systemd-cgls it seems that lightdm.service is in another cgroup than the user sessions with the zellij server. Maybe I am reading this wrong, or both the user and lightdm cgroup are killed?
Simplified output:

-.slice
├─user.slice (#187)
│ └─user-1000.slice (#1870)
│   └─session-2.scope (#2068)
│     ├─   523 lightdm --session-child 12 19
│     ├─   549 xfce4-session
│     └─  1861 /usr/bin/zellij --server /run/user/1000/zellij/0.24.0/grieving-o…
└─system.slice (#55)
  └─lightdm.service (#1507)
    ├─ 445 /usr/bin/lightdm
    └─ 450 /usr/lib/Xorg :0 -seat seat0 -auth /run/lightdm/root/:0 -nolisten tc…

I am not sure if upon logout of the X session the zellij server process gets disconnected from the control group? Because after logout, X/lightdm restarts do not lead to the crash anymore.

[raphCode]

Amazing, even this issue should also be solved by #1351!