[Python-3000] Pre-PEP: Altering buffer protocol (tp_as_buffer)

[Greg Ewing]

Travis Oliphant wrote:

>    2. There is no way for a consumer to tell the protocol-exporting 
> object it is "finished" with its view of the memory and therefore no way 
> for the object to be sure that it can reallocate the pointer to the 
> memory that it owns (the array object reallocating its memory after 
> sharing it with the buffer object led to the infamous buffer-object 
> problem).

I'm not sure I'd categorise this problem that way -- it was
more the buffer object's fault for assuming that it could
hold on to a C pointer to the memory long-term.

I'm a bit worried about having a get/release kind of thing
in the protocol, because it risks forcing all objects which
implement the protocol to provide some kind of refcounting
and locking mechanism for their data. Some objects may not
be able to do that easily or efficiently, especially if
they're wrapping some external library that has no such
notion.

> All that is needed is to create a Python "memory_view" object that can 
> contain all the information needed and be returned when the buffer 
> protocol is called --- when it is garbage-collected, the 
> "bp_release_view" function is called on the exporting object.

That sounds too heavyweight. Getting a memory view through
this protocol should be a very lightweight operation -- ideally
it shouldn't require allocating any memory at all, and it
certainly shouldn't require creating a Python object.

--
Greg