[Zope] Products, Debug manager, and refcounts

[Jim Abramson]

Hello list,

I've done large amounts of googling on the subject, but I can't find any
simple explanation of what the Debug Manager is actually telling me
concerning refcounts.  

It's clear from various sources that, if between REQUESTs one sees a
significant jump for a particular type's refcount, there's clearly a
problem. (Please feel free to correct me if this is an
oversimplification.)  What's not clear is what one should normally
expect.

I make use of some python modules from Zope, generally using the
following pattern:

[python script]
from Products.MyProduct import facademodule
try:
    result = facademodule.doSomething(inputParams)
    return result
finally:
    del facademodule

[facademodule.py]
def doSomething(inputParams):
    import coremodule
    coreObject = coremodule.CoreClass() 
    try:
        resultValue = coreObject.doSomething(inputParams)
        returnValue = {'resultValue':resultValue}
        del resultValue
        return returnValue
    finally:
        del coreObject
        del coremodule

In the above example, I'm making hyper-vigilant use of 'del' to avoid
keeping unneccessary references around.  The facademodule's job is
simply to send back the results of operations using primitive builtin
types (int, list, dictionary) - because a) I don't want my user
interface dependent on the coreObjects' structure; b) coremodule should
be reusable outside the Zope process; and c) I don't want obsolete
object references floating around.

After all this, however, I go to the Debug Manager and see that with
every REQUEST to a page which makes use of this pattern somewhere, the
refcounts for all manner of coremodule's Classes involved in the
facademodule's work appear to be incremented by 1.  (ex. after a REQUEST
using the above pattern I'll see the reference count for
Products.MyProduct.coremodule.CoreClass go up by 1.)

So, is this normal and expected?  Or is it more likely that circular
references in my code are causing the instances to be left hanging
around?  Is there some other approach that's recommended for using my
own objects (residing outside of ZODB) and not bloating RAM, however
slowly this may happen?

Thanks for any clues,
Jim




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