----- Original Message -----
From: "Michael Sparks" <Michaels@rd.bbc.co.uk>
To: <twisted-python@twistedmatrix.com>
Cc: "Paul G" <paul-lists@perforge.com>
Sent: Thursday, January 19, 2006 8:01 AM
Subject: Re: making sqlalchemy work with twisted (was
Re:[Twisted-Python]SQLAbstraction Layer_
On Thursday 19 Jan 2006 03:55, Paul G wrote:
----- Original Message -----
From: "Jean-Paul Calderone" <exarkun@divmod.com>
<exarkun@divmod.com>
new: attribute access -> sqlalchemy accessor -> sqlalchemy
sqlengine ->
async call into dbapi with deferToThread-> control returned to
reactor -> another coop thread gets control
... async dbapi result handler -> return to sqlengine -> return to
accessor -> return attribute
...
Unfortunately, this cannot be implemented in CPython without going
to extreme lengths.
...
Extreme lengths are extension modules that move
On Wed, 18 Jan 2006 21:15:28 -0500, Paul G <paul-lists@perforge.com>
pieces of the C call stack around. See Stackless Python and the >
greenlets module.
yeah, i've looked at those in the past. are you saying they are the only
way to do this and generators won't work?
Generators are really only single layer, unless you start manually
chaining
them which requires changing all the other bits of code.
i'm familiar with what generators are/do ;) my question was really meant to
ask: have you already tried/thought in detail about something similar with
generators and found that it can be done, can't be done or can't be done
cleanly enough to make any sense.
You want to suspend
execution deeper in the call stack which means you'd need Greenlets or
Stackless (or *really* sod about nastily with threads...).
well, the problem with generators is that there's no way to yield several
frames up/down (depending on your arch ;) the stack. so you're talking
trampolines and possibly nasty stack growth if you have to recurse too much
before you can unwind etc. i've started hacking this up, but it's giving me
a headache.
At that point
you're into whether you think that's a good idea or not.
I don't know other people's feelings on the matter, but to me it just
feels
wrong in a system that has clear handoff generally speaking to have some
very hidden handoff as well. At minimum it implies an understanding burden
on the maintainer. At worst you now have the potential to *really* screw
things up.
i'm not arguing for this to be done in twisted, merely seeing if it makes
sense to do locally.
-p
Paul G