#13447: Make libsingular multivariate polynomial rings collectable
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Reporter: nbruin | Owner: rlm
Type: defect | Status:
needs_info
Priority: major | Milestone:
sage-5.4
Component: memleak | Resolution:
Keywords: | Work issues: Input
from libsingular experts
Report Upstream: Reported upstream. No feedback yet. | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:27 nbruin]:
> We have:
> {{{
> def __dealloc__(self):
> celement_destruct(&self.x,
get_cparent((<Polynomial_template>self)._parent))
> }}}
> and for us:
> {{{
> get_cparent(parent) == <ntl_ZZ_pEContext_class>(parent._modulus)
> }}}
> The `_parent` attribute is a cython slot.
Interestingly, there is no complaint about a missing attribute `_parent`.
It is `_modulus` that is missing.
> However, it holds a reference to a python-managed object, so I think
cython ensures it's properly taken into account in GC cycle counting. But
that would suggest to me python could clear this slot to break cycles! So
in that case, `Polynomial_template` is never safe. It could be I'm wrong,
however.
I think you are right. The `__dealloc__` of `Polynomial_template` is
unsafe, unless polynomial rings will stay in memory forever. But I'd love
to hear that we are wrong, because otherwise each polynomial would need a
pointer to the c-data expected to be returned by
`get_cparent((<Polynomial_template>self)._parent)`, and we'd need to take
into account reference counting for the c-parent during creation and
deletion of polynomials.
Or perhaps there is a way out. We have a polynomial ring R and we have
some elements a,b,c,... Each element points to R, and R points to some of
its elements, namely to its generators. The problem is that deallocation
of the elements is only possible as long as R is alive.
If we'd manually incref R upon creation of an element x, decrefing R when
x gets deallocated, then we would ensure that R will survive until the
last of its elements is deleted. Or would that mean that the elements will
survive as well, because of the reference from R to its generators?
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13447#comment:29>
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