[pypy-dev] Freelist in PyPy? Reuse short lived objects?

PIERRE AUGIER pierre.augier at univ-grenoble-alpes.fr
Thu Jan 14 10:34:12 EST 2021


Hello,

I was still playing with the idea to speedup codes using small numerical objects.

I wrote a Cython extension which defines a Point (3d) cdef class and a Points cdef class (a vector of points). Both classes contain a pointer towards a point_ C struct:

ctypedef struct point_:
    float x, y, z

Of course, any computation with Point objects with involved several very short lived objects and we really want to avoid all the associated malloc/free calls.

In Cython, one can decorate a cdef class with `@cython.freelist(8)` to reused objects: https://cython.readthedocs.io/en/latest/src/userguide/extension_types.html#fast-instantiation

I try to add a bit of logic to avoid freeing and allocating the memory for the struct (https://github.com/paugier/nbabel/blob/master/py/microbench/util_cython.pyx). If I understand correctly, doing such things is possible in CPython because the method __dealloc__ is called as soon as the objects is not accessible from Python. Or we can use the fact that it's very fast to get the reference count of an instance. But I think it is not the case for PyPy.

Is there an alternative strategy efficient with PyPy?

Pierre


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