Flask sessions cause tabs to freeze

[GuyShalomCyberRidge]

Hey! 🐶
I have a Flask app and I'm running into a weird issue that I think has to do with sessions - but I'm not sure how.

So when connecting to my web app everything works great and requests flow smoothly. However, if I open another tab of the app in the same browser - all requests in both tabs get stuck in a pending state and the app is unusable. The second that I close one of the tabs, requests start flowing again and all the old pending ones fire instantly.
This doesn't occur when opening multiple tabs in different browsers, or when opening another tab in Incognito, only when it's on the same browser.

How I handle sessions

Session are created on user login -

if(correct_login): #Correct login.
    session["username"] = username
    session["last_modified"] = datetime.now()

I have a before_app_request hook that checks session validity with each request. Every user initiated request also updates last_modified with session["last_modified"] = datetime.now().
Other then that some routes use session data like the username in their process.

All session are stored in a Redis instance. However this issue still persists when using another method like Filesystem.

Is my approach to sessions wrong? Is this a known issue with sessions and I should consider another tool?
Any help would be appreciated 🙏

versions

flask 2.2.5
flask-session 0.8.0
redis 7.4.2

[ranveer9]

Flask-session locks the sessions file or Redis Key for the duration of the request. This is especially visible when both tabs have the same session.
some solutions :

1. Use Flask-KVSessiion with simplekv - it provides better session management without aggressive locking.
2. Instead of session["last_modified"] = datetime.now(), do something like:
   if time.time() - session.get("last_modified", 0) > 30:
   session["last_modified"] = time.time()
   might reduce lock contention by avoiding frequent writes.