[Zope-dev] Re: ComputedAttribute

[Martijn Pieters]

On Wed, Jan 10, 2001 at 11:37:55PM -0000, Chris Withers wrote:
> > Chris Withers writes:
> 
> >  > ....with this class, your_attribute isn't going to play in Persistence,
> >  > is it? (so I can update it lots without worrying about ZODB size
> >  > growing... :-)
> 
> > But, as I understand it, it is only updated in the thread
> > that did the update. Your next request may get a different
> > thread and see a different value.
> 
> Huh?
> 
> If I change self._v_your_attribute it's only going to get updated in one
> thread?
> That's a bit sucky :-S
> 
> Doesn't matter in this _particular_ case 'cos this var gets set at the start
> of every request, but I'm a bit concerned about its general use...
> 
> any help is good help :-)

The whole threading spiel in Zope works because of ZODB persistence; any
thread accessing an object whose variables have been changed has to retry
with a fresh copy from the ODB.

But because _v_* variables don't get pickled, another thread will never
see them. If you want non-persisting (volatile) variables shared between
threads, you'll have to devise your own mechanism for assuring the
thread-safety of those variables.

-- 
Martijn Pieters
| Software Engineer  mailto:mj@digicool.com
| Digital Creations  http://www.digicool.com/
| Creators of Zope   http://www.zope.org/
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