[Cython] Storing many, many instances

[Stefan Behnel]

Dag Sverre Seljebotn wrote:
> Stefan Behnel wrote:
>> Dag Sverre Seljebotn wrote:
>>> Stefan Behnel wrote:
>>>> It might work
>>>> to always use PY_NEW() for instantiation and then generate a separate
>>>> (and direct) call to __init__() only if the type defines it.
>>>>
>>> Should one consider allocating arrays of cdef class objects as one big
>>> memory block?
>>
>> We do not control the allocation, CPython handles that.
>
> OK. I didn't know exactly how fine-grained the CPython API was and
> whether it was possible to run a constructor on already allocated memory
> (like you can do in e.g. C++). It just seemed like that could be one of
> the major bottlenecks.

What we tend to call PY_NEW here is a direct call to a type's tp_new(),
which handles both the allocation and the basic initialisation of an
instance. Cython could do a tiny bit better here, since we know exactly
what function a cdef class has in its tp_new slot. However, that function
will always recursively run into the base type's tp_new and at the end of
the chain into the one of Python's 'type' type, and there is not much we
can do to improve this situation in general.

Stefan