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

User · Accepted Answer

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:
        # 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

User · Answer

First  you should use any WebSocket or polling mechanics to notify the frontend part about changes that happened  I use Flask-SocketIO wrapper  and very happy with async messaging for my tiny apps  Nest  you can do all logic which you need in a separate thread s   and notify the frontend via SocketIO object  Flask holds continuous open connection with every frontend client   As an example  I just implemented page reload on backend file modifications   lt  doctype html gt   lt script gt      sio   io        sio on  reload   info   gt           console log   sio   reload  info           document location reload           lt  script gt   class App Web  Module        def   init   self  V              flask module instance         self flask   flask            wrapped application instance         self app   flask Flask self value          self app config  SECRET KEY     config SECRET KEY             flask-socketio          self sio   SocketIO self app          self watchfiles           inotify reload files after change via  sio reload        def watchfiles self           from watchdog observers import Observer         from watchdog events import FileSystemEventHandler         class Handler FileSystemEventHandler               def   init   self sio                   super     init                     self sio   sio             def on modified self  event                   print  self on modified self event                   self sio emit  reload   event src path event event type event is directory           self observer   Observer           self observer schedule Handler self sio  path  static  recursive True          self observer schedule Handler self sio  path  templates  recursive True          self observer start

User · Answer

In addition to using pure threads or the Celery queue  note that flask-celery is no longer required   you could also have a look at flask-apscheduler   https   github com viniciuschiele flask-apscheduler  A simple example copied from https   github com viniciuschiele flask-apscheduler blob master examples jobs py   from flask import Flask from flask apscheduler import APScheduler   class Config object       JOBS                            id    job1                func    jobs job1                args    1  2                trigger    interval                seconds   10                      SCHEDULER API ENABLED   True   def job1 a  b       print str a          str b    if   name         main         app   Flask   name        app config from object Config         scheduler   APScheduler         it is also possible to enable the API directly       scheduler api enabled   True     scheduler init app app      scheduler start        app run

[python] How can I add a background thread to flask?

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