For flask servers using gunicorn, which can be configured to use any type of worker. We use gevent workers (flag -k) (which use the libuv event loop under-the-hood, see http://flask.pocoo.org/docs/0.12/deploying/wsgi-standalone/): http://docs.gunicorn.org/en/latest/settings.html#worker-class
This means we can push tasks into the gevent event loop and have them execute outside of a flask request context. As long as all the gunicorn workers aren’t processing these tasks and blocking flask request execution, this should not affect performance.