#12313: Fix yet another memory leak caused by caching of coercion data
-------------------------+--------------------------------------------------
Reporter: SimonKing | Owner: rlm
Type: defect | Status: new
Priority: major | Milestone: sage-5.0
Component: memleak | Keywords: coercion weak dictionary
Work_issues: | Upstream: N/A
Reviewer: | Author:
Merged: | Dependencies: #715
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The following could not be fixed in #715:
{{{
sage: K = GF(1<<55,'t')
sage: for i in range(50):
....: a = K.random_element()
....: E = EllipticCurve(j=a)
....: b = K.has_coerce_map_from(E)
....:
sage: import gc
sage: gc.collect()
0
}}}
The problem is that any parent has a dictionary that stores any coerce map
(and a different dictionary for conversion maps) ending at this parent.
The keys are given by the domains of the maps. So, in the example above,
the field `K` has an attribute that is a dictionary whose keys are the
different elliptic curves.
In coercion, it is usually best to compare parents not by equality but by
identity. Therefore, I suggest to implement a container called `MonoDict`
that works similar to the new weak `TripleDict` (see #715), but takes a
single item as a key.
First tests show that one can actually gain a lot of speed: `MonoDict` can
access its items much faster than a usual dictionary. But there is one
slight problem: It happens quite often that a coercion is requested from
the '''integer number''' zero to a parent. But integers don't allow weak
references, and moreover they lack uniqueness.
So, one must either have a special case in the coercion model for the
number zero, or one could argue that it is a bug when the coercion model
requests a coercion whose domain is the integer zero (I am not talking
about the set containing only zero!) and fix that bug.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12313>
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