[SAGA-RG] Python bindings: Buffer class issue

[Mathijs den Burger]

On Sat, 2009-11-14 at 12:04 +0100, Andre Merzky wrote:

> > The real question is: which use cases are we trying to optimize? What
> > will SAGA Python apps do with binary data?
> 
> The primier use asking for optimized I/O on streams and files are
> visualization use cases (you should know *those* use cases, right?
> ;-)  So, an application is repeatedly readong a couple of megabyte
> or so from a stream or a file, into a memory buffer, at say 2*30fps,
> to run some algorithm on the data (say isosurfacer).  
> 
> Now, in the simple case your kernel allocates memory for the read
> you request, and reads data into that memory.  Later, that data is
> copied into your application memory so your app can access the data.
> 
> The buffer object allows to allocate the memory in the application,
> and to pass the buffer down to the kernel, so that it can read data
> directly into the buffer (zero copy: no need to copy it again).
>
> I have no idea how prevalent that use case and similar ones are for
> the python community we are targeting, so its very hard to argue for
> or against that optimization.  Zero Copy is in general useful in
> other use cases, too, but again, it is hard to guesstimate the gain
> without any specific use case to  discuss.

OK, time to wrap up. I propose to NOT include a 'Buffer' class in the
SAGA bindings for Python 2.x (i.e. >= 2.2). Instead of buffers we'll use
strings. Reasons:

1. it is hard to express in Python 2.x (no native 'byte' type, no
'readinto' with a buffer to a pointer, etc.)

2. current users of the C++ Python wrapper do not seem to miss it

3. the number of use cases for buffers is fairly low (GFD.70 and GFD.71
both contain the word 'buffer' only once!)

4. it requires less changes to the C++ Python wrapper code


A dedicated Buffer class MAY be added to a new version of the bindings
for Python 3.x. Reasons:

1. Python 3.x does have a native 'byte' type and methods like 'readinto'

2. New users may desire it


Sounds reasonable?

best,
 Mathijs