Store large data or a service connection per Flask session

The following applies to any global Python data that you don't want to recreate for each request, not just rserve, and not just data that is unique to each user.

We need some common location to create an rserve connection for each user. The simplest way to do this is to run a multiprocessing.Manager as a separate process.

import atexitfrom multiprocessing import Lockfrom multiprocessing.managers import BaseManagerimport pyRserveconnections = {}lock = Lock()def get_connection(user_id):    with lock:        if user_id not in connections:            connections[user_id] = pyRserve.connect()        return connections[user_id]@atexit.registerdef close_connections():    for connection in connections.values():        connection.close()manager = BaseManager(('', 37844), b'password')manager.register('get_connection', get_connection)server = manager.get_server()server.serve_forever()

Run it before starting your application, so that the manager will be available:

python rserve_manager.py

We can access this manager from the app during requests using a simple function. This assumes you've got a value for "user_id" in the session (which is what Flask-Login would do, for example). This ends up making the rserve connection unique per user, not per session.

from multiprocessing.managers import BaseManagerfrom flask import g, sessiondef get_rserve():    if not hasattr(g, 'rserve'):        manager = BaseManager(('', 37844), b'password')        manager.register('get_connection')        manager.connect()        g.rserve = manager.get_connection(session['user_id'])    return g.rserve

Access it inside a view:

result = get_rserve().eval('3 + 5')

This should get you started, although there's plenty that can be improved, such as not hard-coding the address and password, and not throwing away the connections to the manager. This was written with Python 3, but should work with Python 2.