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.
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:
<!doctype html>
<script>
sio = io()
sio.on('reload',(info)=>{
console.log(['sio','reload',info])
document.location.reload()
})
</script>
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()
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()
Source: Stackoverflow.com