Error in event loop with Flask, gremlin python and uWSGI - flask

Question

I'm running into a problem when using Flask with a gremlin database (it's an Amazon Neptune database) and using uWSGI. Everything works fine in my unit tests which use the test_client provided by Flask. However, in production we use uWSGI and there I get the following error:
There is no current event loop in thread 'uWSGIWorker4Core1'.
My app code is creating a connection to the database before a request and assigning it to the Flask g object. During teardown, the database connection is removed. The error happens when the app is trying to close the connection.
from flask import Flask, g
from gremlin_python.structure.graph import Graph
from gremlin_python.driver.driver_remote_connection import DriverRemoteConnection
from gremlin_python.process.anonymous_traversal import traversal
app = Flask(__name__, instance_relative_config=True)
#app.before_request
def _db_connect():
if not hasattr(g, 'graph_conn'):
g.graph_conn = DriverRemoteConnection(app.config['DATABASE_HOST'],'g')
g.gg = traversal().withRemote(g.graph_conn)
# This hook ensures that the connection is closed when we've finished
# processing the request.
#app.teardown_appcontext
def _db_close(exc):
if hasattr(g, 'graph_conn'):
g.graph_conn.close(). # <- ERROR THROWN AT THIS LINE
del g.graph_conn
the uWSGI config does use multiple threads:
[uwsgi]
http = 0.0.0.0:3031
manage-script-name = true
module = dogmaserver:app
processes = 4
threads = 2
offload-threads = 2
stats = 0.0.0.0:9191
But my understanding of how Flask's g object worked would be that it is all on the same thread. Can anyone let me know what I'm missing?
I'm using Flask 1.0.2, gremlinpython 3.4.11 and uWSGI 2.0.17.1.

Answer 1

I used a workaround by removing the threads configuration option in uWSGI which makes there only be a single thread per process.