[Numpy-discussion] Numpy arrays shareable among related processes (PR #7533)

[Sturla Molden]

Antoine Pitrou <solipsis at pitrou.net> wrote:

> Can you define "expensive"?

Slow enough to cause complaints on the Cython mailing list.

> You're assuming this is the cost of "buffer acquisition", while most
> likely it's the cost of creating the memoryview object itself.

Constructing a typed memoryview from a typed memoryview or a slice is fast.
Numerical code doing this intensively is still within 80-90% of the speed
of plain c code using pointer arithmetics.

 
> Buffer acquisition itself only calls a single C callback and uses a
> stack-allocated C structure. It shouldn't be "expensive".

I don't know the reason, only that buffer acquisition from NumPy arrays
with typed memoryviews is very expensive compared to assigning a typed
memoryview to another or slicing a typed memoryview.

Sturla