python - flask application with background threads

Question

I am creating a flask application, for one request I need to run some long running job which is not required to wait on the UI. I will create a thread and send a message to UI. The thread will calculate and update the database. But, UI will see a message upon submit. Below is my implementation, but it is running the thread and then sending the output to UI which is not I prefer. How can I run this thread in the background?

@app.route('/someJob')
def index():
    t1 = threading.Thread(target=long_running_job)
    t1.start()
    return 'Scheduled a job'

def long_running_job
    #some long running processing here

How can I make thread t1 to run the background and immediately send message in return?

Answer 1

Try this example, tested on Python 3.4.3 / Flask 0.11.1

from flask import Flask
from time import sleep
from concurrent.futures import ThreadPoolExecutor

# DOCS https://docs.python.org/3/library/concurrent.futures.html#concurrent.futures.ThreadPoolExecutor
executor = ThreadPoolExecutor(2)

app = Flask(__name__)


@app.route('/jobs')
def run_jobs():
    executor.submit(some_long_task1)
    executor.submit(some_long_task2, 'hello', 123)
    return 'Two jobs were launched in background!'


def some_long_task1():
    print("Task #1 started!")
    sleep(10)
    print("Task #1 is done!")


def some_long_task2(arg1, arg2):
    print("Task #2 started with args: %s %s!" % (arg1, arg2))
    sleep(5)
    print("Task #2 is done!")


if __name__ == '__main__':
    app.run()