How do you add a background thread to flask in Python

Question

I'm trying to write a game server to try out flask. The game exposes an API via REST to users.

It's easy for users to perform actions and query data, however I'd like to service the "game world" outside the app.run() loop to update game entities, etc.

 Given that Flask is so cleanly implemented, I'd like to see if there's a Flask way to do this. Need some help!

Answer 1

The example below creates a background thread that executes every 5 seconds and manipulates data structures that are also available to Flask routed functions.

import threading
import atexit
from flask import Flask

POOL_TIME = 5 #Seconds

# variables that are accessible from anywhere
commonDataStruct = {}
# lock to control access to variable
dataLock = threading.Lock()
# thread handler
yourThread = threading.Thread()

def create_app():
    app = Flask(__name__)

    def interrupt():
        global yourThread
        yourThread.cancel()

    def doStuff():
        global commonDataStruct
        global yourThread
        with dataLock:
        # Do your stuff with commonDataStruct Here

        # Set the next thread to happen
        yourThread = threading.Timer(POOL_TIME, doStuff, ())
        yourThread.start()   

    def doStuffStart():
        # Do initialisation stuff here
        global yourThread
        # Create your thread
        yourThread = threading.Timer(POOL_TIME, doStuff, ())
        yourThread.start()

    # Initiate
    doStuffStart()
    # When you kill Flask (SIGTERM), clear the trigger for the next thread
    atexit.register(interrupt)
    return app

app = create_app()          

Call it from Gunicorn with something like this:

gunicorn -b 0.0.0.0:5000 --log-config log.conf --pid=app.pid myfile:app

Hope this will help!

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Thanks!

Comments

Hi,

Can you re-start the background task from specific routes throughout your app? I want a background task that starts based on the user who logs in into my app. For this, I believe I would need to access flask_login.current_user. How do I do that? Also, I want the background task to start once the user logs in, not before.

Your help would be very appreciated!

Thanks in advance

---

Hi, @Daniel Gutierrez,

Do you want a whole source code where access flask_login.current_user would be mention according to your query?

---

Hello, @Danial,

You can use this below given to login first and then start with background task:

def refresh_user():
    auth_methods = {am.name: am for am in current_app.auth_methods}
    user_auth_method = auth_methods[flask_login.current_user.authmethod]
    if user_auth_method.refresh(flask_login.current_user):
        current_app.logger.debug("Marking '{}' as fresh".format(
            flask_login.current_user))
        flask_login.confirm_login()
        # Call the original endpoint
        view = current_app.view_functions[request.endpoint]
        return view(**request.view_args)
    else:
        flash(login_manager.needs_refresh_message,
                category=login_manager.needs_refresh_message_category)
        original_url = url_for(request.endpoint, **request.view_args)
        return redirect(url_for('login.login', next=original_url,
                _anchor=user_auth_method.safe_name))