Clt+C can be used to stop the Flask app, running on the development server. I would like also to stop the subprocesses that run with the app. With the stop_processes and @app.teardown_appcontext, I have tried to signal the closing of the app and trigger the termination of the subprocesses.

When I press Ctrl+C, the Flask development server stops, however the subprocesses are put to sleep rather than getting termined. Actually, it is the same result as not using the stop_processes function at all.

import flask
import subprocess
import signal
import os

def function1():
    # Create a new subprocess to run 'script1.py', setting it in its own process group
    p = subprocess.Popen(['python', 'script1.py'], preexec_fn=os.setsid)
    p.wait()
    return p
    

def function2():
    # Create a new subprocess to run 'script2.py', setting it in its own process group
    p = subprocess.Popen(['python', 'script2.py'], preexec_fn=os.setsid)
    p.wait()
    return p

app = Flask(__name__)

subprocesses = []

@app.route('/process')
def process():

    global subprocesses
    proc1 = function1()
    subprocesses.append(proc1)
    proc2 = function2()
    subprocesses.append(proc2)

    return "Processing completed!"


@app.teardown_appcontext
def stop_subprocesses(exception=None):

    print('Stopping subprocesses ... ')
    global subprocesses
    for p in subprocesses:
        try:
            # Attempt to kill the entire process group associated with each subprocess
            os.killpg(os.getpgid(p.pid), signal.SIGKILL) 
        except Exception as e:
            print(f"Failed to kill subprocess {p.pid}: {e}")