Starting new subproces from a Flask request

Starting a subprocess with multiprocessing is perfectly acceptable. Here's a minimal working example that uses multiprocessing to update a database in the background. As Audrius states, eventually you'll probably want a proper task queue.

from flask import Flask, jsonifyimport multiprocessingimport datasetimport timeimport randomapp = Flask(__name__)DATABASE_URL = 'sqlite:///dev.db'def add_person(name):    """ Add a person to the db. """    person = {'name': name, 'age': -1, 'status': 'processing'}    db = dataset.connect(DATABASE_URL)    db['people'].insert(person)    return Truedef update_person(name):    """ Update a person in db with a fake long running process     that guesses a random age. """    time.sleep(10)  # simulate a long running process    age = random.randint(1, 120)    person = {'name': name, 'age': age, 'status': 'finished'}    db = dataset.connect(DATABASE_URL)    db['people'].update(person, ['name'])    return Truedef get_person(name):    """ Retrieve a person from the db. """    db = dataset.connect(DATABASE_URL)    person = db['people'].find_one(name=name)    return person@app.route('/<name>')def index(name):    """ Get person. If name not found, add_person to db and start update_person. """    if not get_person(name):        add_person(name)        thread = multiprocessing.Process(target=update_person, args=(name,))        thread.start()    person = get_person(name)    return jsonify(person)if __name__ == '__main__':    app.run(debug=True)

Visit localhost:5000/bert while the subprocess is running:

{    "status": "processing",    "age": -1,    "name": "bert",    "id": 1}

Wait, then refresh and you'll see the subprocess has finished:

{    "status": "finished",    "age": 28,    "name": "bert",    "id": 1}