Sun, 13 Jun 2010 06:54:29 +0200, Sturla Molden wrote:
[clip: memory management only in the interface]
You forgot views: if memory management is done in the interface layer, it
must also make sure that the memory pointed to by a view is never moved
around, and not freed before all the views are freed.
This probably cannot be done with existing Python objects, since IIRC,
they always own their own memory. So one should refactor the memory
management out of ndarray on the interface side.
The core probably also needs to decide when to create views (indexing),
so a callback to the interface is needed.
> Second: If we cannot figure out how much to allocate before starting to
> use C (very unlikely),
The point is that while you in principle can figure it out, you don't
*want to* do this work in the interface layer. Computing the output size
is just code duplication.
> we can always use a callback to Python. Or we can
This essentially amounts to having a
NpyArray_resize
in the interface layer, which the core can call.
Here, however, one has the requirement that all arrays needed by core are
always passed in to it, including temporary arrays. Sounds a bit like
Fortran 77 -- it's not going to be bad, if the number of temporaries is
not very large.
If the core needs to allocate arrays by itself, this will unevitably lead
to memory management that cannot avoided by having the allocation done in
the interface layer, as the garbage collector must not mistake a
temporary array referenced only by the core as unused.
An alternative here is to have an allocation routine
NpyArray_new_tmp
NpyArray_del_tmp
whose allocated memory is released automatically, if left dangling, after
the call to the core is completed. This would be useful for temporary
arrays, although then one would have to be careful not ever to return
memory allocated by this back to the caller.
> have two C functions, the first determining the amount of allocation,
> the second doing the computation.
That sounds like a PITA, think about LAPACK.
--
Pauli Virtanen
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