Signal handlers for SIGINT and SIGTERM are reset to SIG_IGN even when register_sys_signals is disabled

[jzombi]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

My program uses custom signal handlers to terminate the running sanic application and perform other cleanup steps. In earlier sanic versions it worked by running the application with register_sys_signals=False parameter. In the current version it is not working anymore, because the custom signal handler is overwritten by SIG_IGN upon application startup. See:

sanic/sanic/server/runners.py

Lines 159 to 177 in f8e0a72

	def _setup_system_signals(
	app: Sanic,
	run_multiple: bool,
	register_sys_signals: bool,
	loop: asyncio.AbstractEventLoop,
	) -> None: # no cov
	signal_func(SIGINT, SIG_IGN)
	signal_func(SIGTERM, SIG_IGN)
	os.environ["SANIC_WORKER_PROCESS"] = "true"
	# Register signals for graceful termination
	if register_sys_signals:
	if OS_IS_WINDOWS:
	ctrlc_workaround_for_windows(app)
	else:
	for _signal in [SIGINT, SIGTERM]:
	loop.add_signal_handler(
	_signal, partial(app.stop, terminate=False)
	)

According to git blame the behavior changed with this commit: 4499d2c

Code snippet

import os, signal, threading, time

import sanic

def myhandler(signum, frameno):
    print('RECEIVED SIGNAL', signum)

signal.signal(signal.SIGTERM, myhandler)

def periodic_kill():
    for i in range(4):
        print('SENDING SIGNAL', signal.SIGTERM)
        os.kill(os.getpid(), signal.SIGTERM)
        time.sleep(1)
    os.kill(os.getpid(), signal.SIGKILL)

t = threading.Thread(target=periodic_kill, daemon=True)
t.start()

time.sleep(0.5)

app = sanic.Sanic('example')
app.run(host='localhost', port=8765, register_sys_signals=False, single_process=True)

Expected Behavior

Expected output:

SENDING SIGNAL 15
RECEIVED SIGNAL 15
# sanic startup messages
SENDING SIGNAL 15
RECEIVED SIGNAL 15
SENDING SIGNAL 15
RECEIVED SIGNAL 15
SENDING SIGNAL 15
RECEIVED SIGNAL 15
Killed

Actual output: the RECIEVED SIGNAL 15 messages do not appear after sanic startup.

How do you run Sanic?

As a module

Operating System

Linux

Sanic Version

Sanic 23.12.1; Routing 23.12.0

Additional context

No response

[ahopkins]

What's the use case you are after?

[jzombi]

To have different behavior for SIGINT and SIGTERM. I have a complicated application with multiple workers (not sanic workers), each starting its own sanic instance. There is an orchestrator component that manages the workers. The application should terminate nicely when CTRL-C is pressed. The shut-down process is managed by the orchestrator, workers should not terminate themselves on SIGINT.

What is the reason behind forcefully setting SIG_IGN?