How to break out of an infinite loop with flask and python using http?

Question

I would like to break out of an infinite loop using flask and a http get.

from flask import Flask, render_template, jsonify
from serialtest import get_dist
app = Flask(__name__)

def test():
    while True:
        print('keep going!')

@app.route('/start')
def start():
    return test()

@app.route('/stop')
def stop():
    # stop the function test
    return 'stopped'

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=5000, debug=True, threaded=True)

I want to use Flask as a http server and serve a web client that can start test() with a click event and http get, then stop test() with a different click event.

Answer 1

For this particular case you can spawn a thread that handles the long running task. i.e.,

import threading
import time
from flask import Flask, render_template, jsonify
from serialtest import get_dist
app = Flask(__name__)

light_on = False

@app.before_first_request
def light_thread():
    def run():
        global light_on
        while light_on:
            print("keep going!")
            time.sleep(1)

    thread = threading.Thread(target=run)
    thread.start()

@app.route('/start')
def start():
    # stop the function test
    light_on = True
    return "started"

@app.route('/stop')
def stop():
    light_on = False
    return 'stopped'

if __name__ == "__main__":
    app.run(host='0.0.0.0', port=5000, debug=True, threaded=True)

The thread runs as long as the server itself is running and is started before any HTTP request is made to the server using the before_first_request decorator. It checks the on/off state in a global variable. I wouldn't recommend this, specifically using the global variable to save state, for all scenarios but this should accomplish the use case you've described.