global (accessible anywhere), but per-request variable

rubyonrails-talk
1

If I understand it correctly it would be enough to initialize something global like a singleton, $global, whatever, with a filter in ApplicationController. If you need it outside the web app, e.g. in the console, it could have some default set in environment.rb.

-- fxn

2

Hi Jenda,

And I don't think initializing a $global would work. What if two requests come at about the same time? Request A inicializes the $global, request B inicialized the $global, and then requst A used the $global using the level and other settings set by request B? No thanks!

I don't think that's going to be a problem.

Your web server might be able to process multiple requests simultaneously, but that's probably because it's got multiple dispatch.fcgi processes running. But each of those processes runs in a strictly serial fashion. Rails doesn't somehow start processing the next request while the previous one is still finishing, so don't worry about that.

I know I can use a before:filter to get a snippet of code ran at the start of the request processing, what I don't know is where to store the stuff then so that it's global as "accessible from anywhere" but request-specific.

Any module or class that's loaded is available throughout all your models, views and controllers etc., so if you set a class variable on a module or class it will be available anywhere; you can then clean it up in an after-filter so it doesn't persist into the next request.

Regards, Dave

3

Yeah, the assumption you miss is that Rails is single-thread multi-process. Two dynamic requests cannot be served at the same time by the same Ruby interpreter.

-- fxn