[Zope] memory leak in a very simple product. Way?

[Thomas B. Passin]

[Christoph Wierling]
>
> I've writte a very simple product which creates 100 simple objects
> (testProd class instances) and each of these objects has a list-attribute
> which contains 200 other objects (item class instances). (Please find the
> code at the end of this mail.)
> By starting the addTestProd-function I create 20000 references to
> item objects, as the Zope-debug option as well as the leakFinder-product
> tell me.
> But I'll never get rid of these references and earlier or later I'll run
> out of memory.
>
> Could anybody explain me, way this simple product is leaking like a sieve?
> And how I can get rid of the references?
>
>
> here is the code:
>
> ...

> class testProd(SimpleItem.SimpleItem):
>     """ testProd docu """
>
>     meta_type = 'testProd'
>
>     def __init__(self, id, title = ''):
>         self.id = id
>         self.title = title
>
>         self._tree = []
>
>         for i in xrange(200):
>             n = item(str(i),i)
>             tree = self._tree
>             tree.append(n)
>             self._tree = tree
>

I think you really want to do this:

         tree = []
         for i in xrange(200):
             n = item(str(i),i)
             tree.append(n)
         self._tree = tree

I'm concerned about the statement

        self._tree = tree

With your version, self._tree is assigned to tree, which is modified, then
assigned back to self._tree.  Maybe that's OK, but it makes me concerned
that each time around a circular reference may be created.  If so, there's
your leak.

Cheers,

Tom P