#14711: Memleak when creating QuadraticField
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Reporter: jpflori | Owner:
Type: defect | davidloeffler
Priority: critical | Status: new
Component: number fields | Milestone: sage-5.12
Keywords: memleak, number field, | Resolution:
QuadraticField | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: u/SimonKing/ticket/14711 | Commit:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Yes, we have run into these things repeatedly. We're storing maps as
`_coerce_from` and `_convert_from` on the codomain because for those maps,
the codomain needs the domain to exist anyway (a polynomial ring will be
holding a reference to its coefficient ring, a quotient ring needs the
ring it was quotiented from).
This goes very wrong when we have maps into LARGER rings that exist
independently. Indeed, as soon as you're coercing/converting/embedding a
number field into Qbar, into SR, or into CC, your ring has been damned
with virtually eternal life (SR is one ring to forever in the darkness
bind them...).
A nasty solution is to ALSO have _coerce_to and _convert_to, store each
map in only one, and in the discovery process look on both the domain and
the codomain. One can then choose whether the map should be cached on the
domain or the codomain (depending on which one is expected to have the
longer natural line). We'd end up mostly using the `_*_from` variants as
we have now, but for things like QQbar etc. we'd choose the other one.
This might reduce the number of times where we'll get a leak this way, but
I suspect that it'll be possible to get strong reference cycles via this
process nonetheless.
--
Ticket URL: <http://trac.sagemath.org/ticket/14711#comment:28>
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