#12941: Cache should be cleared on cloning
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Reporter: hivert | Owner: hivert
Type: defect | Status: new
Priority: major | Milestone: sage-5.1
Component: combinatorics | Resolution:
Keywords: Clone, cache, days38 | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Florent Hivert | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:14 hivert]:
> - I'm Ok to implement a ``copyAndClearTheCache`` at the level of
``Element``
> or ``ClonableElement``. Any support from the cache mechanism which
makes it
> as fast as possible is welcome.
I hope that the `clear_cache` method of cached methods is quick enough:
{{{
sage: class A:
....: @cached_method
....: def f(self):
....: return 5
....: @cached_method
....: def g(self,i,n=4):
....: return i**n
....:
sage: a = A()
sage: %timeit a.f.clear_cache()
625 loops, best of 3: 182 ns per loop
sage: %timeit a.g.clear_cache()
625 loops, best of 3: 328 ns per loop
}}}
> - On the second stage I don't want to clear the cache upon any
modification as
> they are supposed to be elementary (eg: modifying an array entry). As
a
> consequence, I'd like to have a hook which **deactivate any caching on
> mutable objects**. Caching will be be reactivated once the object is
set
> immutable. Do you think that's feasible on the ``CachedMethod`` side
while
> keeping the overhead as low as possible ?
One could certainly create a new decorator, say, @cache_if_immutable, that
only writes to or reads from the cache if the object is immutable. I have
no idea of the overhead (at least, one would have one call to
_is_immutable() per access).
> Currently all sage mutable objects including not only clones but
matrices and
> vectors have a method ``_is_immutable``. Vectors and matrices implements
> their own caching mechanism, but I think having cached method work with
them
> would be good.
Technical difficulty: cached_method requires that either the object allows
to set new attributes, or it has an attribute `__cached_methods` which is
a dictionary. The latter exists for sage.structure.parent.Parent, by
#11115.
Now the problem is that vectors (such as created by `vector(CC, [1,2,3])`)
do ''not'' support adding attributes, and they do not have
`__cached_methods`. By consequence, @cached_method will not work for them.
A possible solution would be to add `cpdef dict __cached_methods` to
vectors. But then, the next complication arises:
{{{
sage: cython("""
....: from sage.structure.parent cimport Parent
....: cdef class MyParent(Parent):
....: def f(self):
....: return 5
....: """)
sage: MyParent.f.__module__
---------------------------------------------------------------------------
AttributeError Traceback (most recent call
last)
/home/simon/SAGE/work/pathalgebras/<ipython console> in <module>()
AttributeError: 'method_descriptor' object has no attribute '__module__'
}}}
Unfortunately, the `__module__` attribute is read when a cached method is
defined. Hence, although cached_method does work for a python class
defined in a cython module, it does not (yet) work on a cdef class.
But one could try to work around:
{{{
sage: MyParent.f.__objclass__.__module__
'_home_simon__sage_temp_linux_sqwp_site_4700_tmp_2_spyx_0'
}}}
So, I guess I'll open another cached_method ticket!
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/12941#comment:15>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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