[Erp5-dev] Cache on skin tool

[Pelletier Vincent]

Hi.

I commited a cache I wrote for skin tool.

This cache should be completely transparent : apart from cache populating 
which costs some time, cache updates are handled and no manual invalidation 
is required. Its use is implicit an no code need to be changed to use it.

Cache populating is done in 3 cases
- site startup (once per thread)
- skin selection change (portal_skins/manage_propertiesForm)
- when portal_skins object is modified

I've been the only user of this cache yet, so it can contain bugs I didn't 
trigger. If you suspect this cache causes problems on your site or if you 
want to disable it for a reason or another, you just have to comment out the 
following lines in ERP5Type/ZopePatch.py and restart your zope.

from Products.ERP5Type.patches import CMFCoreSkinnable
from Products.ERP5Type.patches import CMFCoreSkinsTool
from Products.ERP5Type.patches import OFSFolder

Cache internals
It's not required to know how this cache operates since it's completely 
transparent. Though, as there might be bugs, this description might help 
finding if the bug comes from the caching system or not.
Caching is done in a volatile dictionary of dictionaries.
Outermost dictionary keys are Skin Selection Names (View, Print, CSV, ...), 
innermost dictionary keys are existing object ids, and the value is the id of 
their container.
OFS Folder class is patched so that when an object is attached to a Folder 
object *and* this Folder is right below portal_skins tool the cache gets 
updated.
As the cache is stored in a volatile property of skin tool, it's lost each 
time skin tool is modified (adding a subobject, ...) or reloaded from ZODB 
(another node in a zeo setup updated the object, ...).

-- 
Vincent Pelletier