How can I add a background thread to flask?

Question

I'm busy writing a small 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.

Answer 1

Your additional threads must be initiated from the same app that is called by the WSGI server.

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:             pass             # 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