[Zope-dev] Infuriating ZClass registry Heisenbug

[Shane Hathaway]

On 12/10/2002 09:58 PM, Evan Simpson wrote:

> Shane Hathaway wrote:
>
> > My first recommendation would be to turn your ZClass registry into an
> > OOBTree.  OOBTree has been maintained and updated.
>
>
> Good thought, but no dice.

Well, it was worth a shot. :-)

> Since it is rebuilding the registry on every restart anyway, I went
> ahead and made the changes to my OFS/Application.py.  I confirmed that
> ZGlobals is now an OOBTree, but subsequent restarts continue to show the
> same problem :-(
>
> I've placed pdb.set_trace all over the DB state-loading code.  When I
> attempt to step into the "state = unpickler.load()" line during the
> loading of the ZGlobals OOBTree, it immediately throws an ImportError on
> the ZClass GUID.  It doesn't even seem to enter the persistent_load or
> classLoader methods.

Shot in the dark #2: Does it enter the ClassFactory function in 
Zope.ClassFactory?  That's part of the ZClass magic... although there 
are two ways that the pickler tries to load classes.  ZODB only tries to 
load Persistent instances as ZClasses.  If there are things inside the 
pickles that are not Persistent, yet come from a ZClass, ZODB will not 
treat them kindly.

Shot in the dark #3: Unfortunately, there's one bit of ZODB that I still 
don't fully understand, and that's setklassstate().  You might be 
running into this somehow.  I'd hazard a guess that the latest 
cPickleCache does not do the right thing with setklassstate(), since no 
one has committed to maintain that part.  Ugh, we need unit tests for that.

> Tracing this has gotten me all confused.  I understand (I think) that
> when a ZClass instance is unpickled, persistent_load gets the ZClass
> GUID and uses that to look up the actual _zclass_ class in ZGlobals.
> What I can't understand is why it would try to import the GUID when
> loading ZGlobals.  All it has it in is strings and the _zclass_
> ExtensionClasses, and they should be handled by the normal unpickling
> machinery, right?

Sounds right, although I've forgotten the details.

Here's a simple suggestion: after loading the site and browsing a few 
pages involving ZClasses, flush the ZODB cache and see if the bug 
appears right away.  If so, it's probably occurring as a result of 
deactivation.

Shane