Kill process and all its child processes after a Popen

Question

So I have a situation where I have an Flask endpoint A, endpoint B and two other scripts foo.py and bar.py.

When I call endpoint A, I will do a call for foo.py with Popen and store its PID. On foo.py, it makes a call to bar.py using Popen, which makes another call, again, using Popen. The process opened on bar.py is a server (to be more specific, it's a tf-serving server), which will be hanging forever when I do an p.wait(). Later on, I would like to use endpoint B to end the whole process triggered by A.

The situation can be something like:

Flask's endpoints:

import os
import json
import signal
from subprocess import Popen

from flask import current_app
from flask import request, jsonify

@app.route('/A', methods=['GET'])
def a():
    p = Popen(['python', '-u','./foo.py'])
    current_app.config['FOO_PID'] = p.pid
    return jsonify({'message': 'Started successfully'}), 200

@inspection.route('/B', methods=['GET'])
def b():
    os.kill(current_app.config['FOO_PID'], signal.SIGTERM)
    return jsonify({'message': 'Stopped successfully'}), 200

foo.py:

p = Popen(['python' ,'-u', './bar.py', '--serve'])
while True:
   continue

bar.py:

command = f'tensorflow_model_server --rest_api_port=8501 --model_name=obj_det --model_base_path=./model'
p = subprocess.Popen(command, shell=True, stderr=sys.stderr, stdout=sys.stdout)
p.wait()

Unfortunately when I kill foo.py using endpoint B, the process created by bar.py (ie. the server) will not end. How can I kill the server?

Please consider a solution that is OS agnostic.

ok, on B endpoint, use the PID of A to track its availability. I also tell you to uniquely name your process so when you track A from B also check to see if A has the good name. if A is ended then also ends B — Narcisse Doudieu Siewe, May 15 '20 at 22:46
take a look here https://stackoverflow.com/questions/7787120/python-check-if-a-process-is-running-or-not — Narcisse Doudieu Siewe, May 16 '20 at 03:42

score 2 · Accepted Answer · answered May 16 '20 at 04:29

Using a package like psutil allows you to recursively iterate and access of all child processes related to a certain PID. This will effectively allow you to kill all nested processes. Documentation for psutil https://github.com/giampaolo/psutil.

import json
import signal
from subprocess import Popen

from flask import current_app
from flask import request, jsonify
from psutil import Process

@app.route('/A', methods=['GET'])
def a():
    p = Popen(['python', '-u','./foo.py'])
    current_app.config['FOO_PID'] = p.pid
    return jsonify({'message': 'Started successfully'}), 200

@inspection.route('/B', methods=['GET'])
def b():
   pid = current_app.config['FOO_PID']
   parent = Process(pid)
   for child in parent.children(recursive=True):
      child.kill()
   parent.kill()
   return jsonify({'message': 'Stopped successfully'}), 200

Kill process and all its child processes after a Popen

1 Answers1