[Web-SIG] Alternative to threading.local, based on the stack

[Ian Bicking]

Iwan Vosloo wrote:
> Many web frameworks and ORM tools have the need to propagate data
> depending on some or other context within which a request is dealt with.
> Passing it all via parameters to every nook of your code is cumbersome.
> 
> A lot of the frameworks use a thread local context to solve this
> problem. I'm assuming these are based on threading.local.  
> 
> (See, for example:
> http://www.sqlalchemy.org/docs/05/session.html#unitofwork_contextual )
> 
> Such usage assumes that one request is served per thread.
> 
> This is not necessarily the case.  (Twisted would perhaps be an example,
> but I have not checked how the twisted people deal with the issue.)

The Spawning server 
(http://ulaluma.com/pyx/archives/2008/06/spawning_01_rel.html) would 
indeed get things mixed up this way, as uses greenlets to make (at least 
some) blocking calls async.  So it would encounter this problem full-force.

To throw another wrench in things, with the Paste/WebError evalexception 
interactive exception handler, it restores this thread-local context so 
you can later execute expressions in the same context.

-- 
Ian Bicking : ianb at colorstudy.com : http://blog.ianbicking.org