Are there any concerns I should have about storing a Python Lock object in a Beaker session?

Question

There is a certain page on my website where I want to prevent the same user from visiting it twice in a row. To prevent this, I plan to create a Lock object (from Python's threading library). However, I would need to store that across sessions. Is there anything I should watch out for when trying to store a Lock object in a session (specifically a Beaker session)?

Answer 1

I just realized that this was a terrible question since locking a lock and saving it to the session takes two steps thus defeating the purpose of the lock's atomic actions.

Answer 2

Storing a threading.Lock instance in a session (or anywhere else that needs serialization) is a terrible idea, and presumably you'll get an exception if you try to (since such an object cannot be serialized, e.g., it cannot be pickled). A traditional approach for cooperative serialization of processes relies on file locking (on "artificial" files e.g. in a directory such as /tmp/locks/<username> if you want the locking to be per-user, as you indicate). I believe the wikipedia entry does a good job of describing the general area; if you tell us what OS you're running order, we might suggest something more specific (unfortunately I do not believe there is a cross-platform solution for this).