Question

I’m creating a simple web game that uses web sockets for to stream updates HTTP AJAX requests for everything else (e.g. login system, user profiles, &c). Unfortunately I’m somewhat new to mod_python, but it seems that I want to use the Sessions class to keep track of visitors. The only problem is that a Session requires a mod_python request for some reason. Is there a way I can use these sessions within a mod_pywebsocket handler, or do I need to roll my own session mechanism?

Answer 1

In case anyone could use this, I’ve found that mod_python’s sessions work quite well with mod_pywebsocket. Here are two considerations to be aware of:

Initialization Typically, you construct a mod_python Session object with a mod_python request. Luckily, the authors of mod_pywebsocket had the forethought to make the web socket requests (the ones you get in web_socket_transfer_data arguments) compatible. That means you can instantiate your Session in the same way you normally would in mod_python (see the docs for examples). This might seem obvious, but it wasn’t to me. If you get an error doing this, you’ve done something else wrong.

Session locks The other thing to keep in mind is that the session associated with a given ID is locked by default, and the lock persists for the lifetime of that Session object. This means that if you have two web sockets that use Sessions from the same host, one of them is in danger of blocking forever. In addition, the documentation states that these mutex locks can require non-trivial system resources. They were clearly designed for serving quick HTTP requests, not for persistent connection-oriented use.

One way to fix sessions is to disable the locking, but that’s probably not a smart thing to do. I haven’t tried it, but best of luck with those race conditions if you make the attempt. What I did was to create the Sessions I needed only for short periods of time and then assign None to it when I was done. Apparently with clauses won’t work with these sessions. Again, this isn’t terribly obscure, but it can lead to some headaches if you don’t realize what’s going on under the hood.