How can I return a Flask redirect while wating for a request to complete?

Question

I have a Flask app with a view function that is set up like this (MWE):

from flask import redirect
import time, random

def quick_processing_function():
    return True

def long_processing_function():
    time.sleep(15)
    return random.rand() < 0.99

@app.route('target')
def function():
    result = quick_processing_function()
    if result:
        long_processing_function_that_may_fail()
        return redirect(SOME_EXTERNAL_SITE)

I'd like long_processing_function_that_may_fail() to not delay the service of the redirect to the external site, especially if it fails to complete. But it must run. Ideally, long_processing_function_that_may_fail() would run after the redirect is sent to the user. What's the best way to meet these requirements?

Answer 1

You can do it in a separate thread

from flask import redirect
import threading
import time, random

def quick_processing_function():
    return True

def long_processing_function():
    time.sleep(15)
    return random.rand() < 0.99

@app.route('target')
def function():
    result = quick_processing_function()
    if result:
        x = threading.Thread(target=long_processing_function_that_may_fail, args=())
        x.start()
        return redirect(SOME_EXTERNAL_SITE)