Question

I have a django app which is used for managing registrations to a survey.

There are fixed number of slots and I want to “reserve” slots for users when they sign up.
In one of my views, I get the next available slot and reserve it (or redirect the user if there are no slots available.)

I want to protect against the case where two user’s signing up at the same time get registered for the same slot because the the method “get_next_available_slot” returned the same slot for both users.

For this I am trying to understand the use of processes and threads with Django’s views.

1) Is each request handled in a separate thread and will using python threading module’s LOCK() take care of exclusive access?

2) I am running apache on RHEL with modwsgi. How do I configure Apache/modwsgi to ensure a more easy and simple solution to handle the above situation?

I am not expecting a huge load on the web application at all. So I would like a simpler solution instead of a high performance one.

Answer 1

You should not make assumptions about thread/process setup of django application, because it depends on web server you’re using and how django is integrated to it. Therefore, interprocess communication methods should not rely on these details to be reliable. One good solution is using built-in cache library for locks and shared data.

Here’s a good example of cache lock ensuring only once instance of celery task is run at a time. You can apply it to regular requests as well.