Helper program to terminate processes gracefully.
I was making a GUI program in Python and wanted to run console apps without any window and terminate them gracefully. No big deal on Linux and Mac, you just send SIGINT. But Windows makes it hard. You need to create a subprocess with CREATE_NEW_PROCESS_GROUP flag and then you can send CTRL_BREAK_EVENT. But that event doesn't work with everything, you won't stop ping with it, you need CTRL_C_EVENT. But the default handler for that event is disabled when you use CREATE_NEW_PROCESS_GROUP flag. And if you add PyInstaller into the mix then even CTRL_BREAK_EVENT stops working (unless I missed some flag).
You can read more about that mess here:
https://bugs.python.org/issue33245
https://bugs.python.org/issue23948
Code for gracefully killing used in the example below and in ctrlc itself taken from:
https://stackoverflow.com/a/60795888/2428152
Below is the example use. ctrlc.exe is used only on Windows and if the code is frozen with PyInstaller.
import os
import sys
import signal
import subprocess
import threading
from time import sleep
from functools import partial
def terminate(p):
p.terminate()
print("terminated", p.args)
if os.name == 'nt':
DEFAULT_KWARGS = {
"creationflags": subprocess.CREATE_NEW_CONSOLE,
"startupinfo": subprocess.STARTUPINFO(
dwFlags=subprocess.STARTF_USESHOWWINDOW, wShowWindow=subprocess.SW_HIDE
),
}
else:
DEFAULT_KWARGS = {}
if __name__ == "__main__":
p = subprocess.Popen(
[
"aria2c",
"-o",
r"test.iso",
"https://releases.ubuntu.com/20.04.3/ubuntu-20.04.3-desktop-amd64.iso"
],
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
**DEFAULT_KWARGS,
)
sleep(5)
if os.name == 'nt': # Windows
if getattr(sys, 'frozen', False): # when using PyInstaller
command = ["ctrlc"]
else:
command = [
sys.executable,
"-c",
"import ctypes, sys;"
"kernel = ctypes.windll.kernel32;"
"pid = int(sys.argv[1]);"
"kernel.FreeConsole();"
"kernel.AttachConsole(pid);"
"kernel.SetConsoleCtrlHandler(None, 1);"
"kernel.GenerateConsoleCtrlEvent(0, 0);"
"sys.exit(0)",
]
p2 = subprocess.Popen([*command, str(p.pid)], **DEFAULT_KWARGS)
watchdog = threading.Timer(5, partial(terminate, p2))
watchdog.start()
p2.wait()
watchdog.cancel()
else: # Linux or Mac
p.send_signal(signal.SIGINT)
watchdog = threading.Timer(5, partial(terminate, p))
watchdog.start()
exitcode = p.wait()
watchdog.cancel()
print(exitcode) # should be 7 if the download link is correct
# save to file in case PyInstaller is used with `--noconsole`
with open("exitcode.txt", "w") as f:
f.write(str(exitcode))
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