SIGHUP signal not raises exit immediately

[FlyingWombat]

I'm not sure if this is an alacritty issue, or a xonsh issue, so I'm starting here.
When using alacritty in single-instance mode, xonsh processes remain if their parent window is closed by the window manager (e.g. Meta+Q for Sway). I've only been able to find this issue when using both alacritty in single-instance mode and xonsh. Alacritty single-instance with Zsh works as expected, alacritty individual instances works with xonsh, and xonsh with foot's single-instance mode works. The issue also does not occur if xonsh has a parent process other than alacritty (e.g. alacritty -> zsh -> xonsh)

Expected Behavior

Xonsh processes should exit when parent window closes.

Current Behavior

Xonsh process remains when parent window is closed.

Steps to Reproduce

1. export SHELL=$(which xonsh) if xonsh isn't your default shell.
2. Start an alacritty instance with alacritty --socket /tmp/alacritty.sock
3. Create a second alacritty window with alacritty msg --socket /tmp/alacritty.sock create-window. This creates a new terminal attached to the same instance of alacritty. Notice now there are two xonsh processes attached to the same alacritty process.
4. (optional) run some command in the second terminal window to help identify it (e.g. man bash).
5. Close the second terminal window using the window manager instead of exiting xonsh directly. Notice there are still two xonsh processes attached to the alacritty process.

xonfig

+------------------+----------------------------------+
| xonsh            | 0.16.0                           |
| Python           | 3.11.9                           |
| PLY              | 3.11                             |
| have readline    | True                             |
| prompt toolkit   | 3.0.40                           |
| shell type       | prompt_toolkit                   |
| history backend  | sqlite                           |
| pygments         | 2.17.2                           |
| on posix         | True                             |
| on linux         | True                             |
| distro           | unknown                          |
| on wsl           | False                            |
| on darwin        | False                            |
| on windows       | False                            |
| on cygwin        | False                            |
| on msys2         | False                            |
| is superuser     | False                            |
| default encoding | utf-8                            |
| xonsh encoding   | utf-8                            |
| encoding errors  | surrogateescape                  |
| xontrib 1        | vox                              |
| xontrib 2        | coreutils                        |
| xontrib 3        | voxapi                           |
| RC file 1        | /etc/xonsh/xonshrc               |
| RC file 2        | /home/wombat/.config/xonsh/rc.xsh |
+------------------+----------------------------------+

System

Distro: Nixos
WM: Sway 1.9
Alacritty: 0.13.2

For community

⬇️ Please click the 👍 reaction instead of leaving a +1 or 👍 comment

[anki-code]

JFYI to trace this you can use this message - #5361 (comment)

[FlyingWombat]

Error: Custom { kind: ConnectionRefused, error: "invalid socket path "/tmp/alacritty.sock"" }

Strange. Maybe Mac has some weird rules about where sockets can be. The socket can be anywhere, I just used /tmp/ for an example.

Using the signal-catch.py example, with export SHELL="$PWD/signal-catch.py", it appears that alacritty is sending a SIGHUP when the window is closed. But, that simple check doesn't show any different behavior between alacritty running normally (one process per window) and in single-instance (one process all windows); it just shows a single SIGHUP for ether one.

Turns out the strace logs are much shorter on Arch Linux (only 250 lines), so I'm attaching them here.

Regular alacritty (xonsh closes):
xonsh-strace-normal-closes.txt

single-instance (doesn't close):
xonsh-strace-daemon-noclose.txt

[anki-code]

Good catch @FlyingWombat !

alacritty is sending a SIGHUP when the window is closed

And:

SIGHUP ("signal hang up") is a signal sent to a process when its controlling terminal is closed.

Next you can run xonsh in debug mode in IDE, then run kill -SIGHUP <pid>(doc) and review what xonsh is doing with this signal. The start point is looking for signal.signal(...) (set signal handler) and signal.SIGHUP lines (Cmd+Shift+F to search substring around the whole code).

[anki-code]

I got this on mac:

# Terminal 1
xonsh --no-rc  

# Terminal 2
ps ax | grep 'xonsh --no-rc'
# xonsh pid 100
kill -SIGHUP 100

# Terminal 1
#zsh: hangup     xonsh --no-rc

# Terminal 2
ps ax | grep 'xonsh --no-rc'
# xonsh in S (sleep) state and pid is 101

On the second try:

# Terminal 1
xonsh --no-rc   # pid 123

# Terminal 2
kill -SIGHUP 123

# Terminal 1
# ...
#  File "/Users/pc/.local/xonsh-env/lib/python3.12/asyncio/base_events.py", line 685, in run_until_complete
#    return future.result()
#           ^^^^^^^^^^^^^^^
#  File "/Users/pc/.local/xonsh-env/lib/python3.12/site-packages/prompt_toolkit/application/application.py", line 649, in run_async
#    assert not self._is_running, "Application is already running."
#AssertionError: Application is already running.
#Xonsh encountered an issue during launch
#Failback to /bin/zsh

It looks like there is no catching and processing SIGHUP signal. PR is welcome!

[anki-code]

I've understood the case:

1. When you send SIGHUP this handler is working (line 62 do sys.exit()):

xonsh/xonsh/built_ins.py

Lines 47 to 64 in 4a2cfc6

	if ON_POSIX:
	sigs += (signal.SIGTSTP, signal.SIGQUIT, signal.SIGHUP)
	return sigs
	def resetting_signal_handle(sig, f):
	"""Sets a new signal handle that will automatically restore the old value
	once the new handle is finished.
	"""
	oldh = signal.getsignal(sig)
	def newh(s=None, frame=None):
	f(s, frame)
	signal.signal(sig, oldh)
	if sig != 0:
	sys.exit(sig)
	signal.signal(sig, newh)

2. The sys.exit() function in fact just raises SystemExit exception.

3. This exception catched by the shell e.g. ptk:

xonsh/xonsh/ptk_shell/shell.py

Lines 413 to 414 in 4a2cfc6

	except (KeyboardInterrupt, SystemExit):
	self.reset_buffer()

4. And nothing happends on first SIGHUP.

We need to pass forward the SystemExit futher.

Nice catch. I will prepare PR to fix this. Thank you for reporting @FlyingWombat !

[anki-code]

@FlyingWombat could you please try #5399?

xpip install -U --force-reinstall git+https://github.com/xonsh/xonsh@sig_exit_fix

[anki-code]

Originally posted by @FlyingWombat in #5399 (comment):

Tried this out, and while it is exiting when sent SIGHUP now, it doesn't always exit properly. What I noticed is, after xonsh exits, zsh no longer recognizes Ctrl+C.

When kill -SIGHUP 1234 is run from xonsh itself, it exists correctly (zsh works fine after). But running kill -SIGHUP 1234 from another terminal running e.g. zsh, goes like this:

# running zsh, launch xonsh
xonsh on  sig_exit_fix [?] via 🐍 v3.12.3 (.venv)
❯ xonsh

# send SIGHUP
(.venv) wombat@wombat-pc ~/builds/dev/xonsh sig_exit_fix @ 
%

xonsh on  sig_exit_fix [?] via 🐍 v3.12.3 (.venv) took 14s
❯ ^C^C
# zsh no longer recognizes Ctrl+C

If I do the same thing with bash, zsh is working properly afterwards.

[anki-code]

@FlyingWombat thanks for help!
I can repeat this on Mac with iTerm2 or Alacritty:

# Terminal 1
# Run iTerm or Alacritty with zsh as default shell
xonsh -DFFF=1

# Terminal 2
ps ax | grep FFF  # xonsh pid 123
kill -SIGHUP 123

# Terminal 1
# Return zsh
# Ctrl+C is not working and Mouse Scroll produces `10M35;`
stty sane
# Everything is working

It looks that in 5399 I solved exit code issue and xonsh exit is correct but something is needed to restore terminal state.

The readline shell type works good after catching signal so we need to fix PTK:

# use the latest commit from 5399
xpip install -U --force-reinstall git+https://github.com/xonsh/xonsh@sig_exit_fix
xonsh -st readline

[anki-code]

@FlyingWombat I fixed stty state for ptk, please test again:

xpip install -U --force-reinstall git+https://github.com/xonsh/xonsh@sig_exit_fix
# restart xonsh
xonfig 
# Git SHA | 5fa579a # https://github.com/xonsh/xonsh/pull/5399/commits

[FlyingWombat]

Exit signals are working with that PR. Thanks for your help!