[Python] Pywebview blocks flask app unless I open two webviews

I built a python desktop webapp with a fairly simple flask backend which I'm currently serving simply through Chrome. I'm trying to package it using pywebview, but I ran into an intestesting roadblock.

I have code that looks like this in the main file of my package:

import os
import sys
from flasher import app

import httplib

import webview
import threading


def start_prod_server():
runserver(debug=False, reloader=False)

def start_gui():
webview.create_window("MyAppName", "http://localhost:5000", height=1000)

def runserver(debug=True, reloader=False):
port = int(os.environ.get('PORT', 5000))
url = "http://localhost:{}".format(port)

print("ready!")
app.run(host='::', port=port, debug=debug, use_reloader=reloader)


if __name__ == '__main__':
t = threading.Thread(target=start_prod_server)
t.daemon = True
t.start()

# This never works
threading.Timer(1.5, start_gui).start()

sys.exit()


This fails almost systematically, the window shows up blank and the backend doesn't respond to anything (including requests from a separate desktop browser).

I discovered accidentally that if I start two webview threads, it always works:

if __name__ == '__main__':
t = threading.Thread(target=start_prod_server)
t.daemon = True
t.start()

# This works every time
threading.Timer(1.5, start_gui).start()
threading.Timer(1.5, start_gui).start()

sys.exit()


What could be causing this? My understanding of threading in Python is fairly limited, so I'm not sure where to look. Is this likely to be a bug in pywebview, or am I doing something wrong with my threads?

I'm also open to suggestions of alternatives for the webview part, but I want to keep the python/flask part since the app already works fine as it is.

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