Parallel processing

[Josiah Carlson]

bearophileHUGS at lycos.com (bearophile) wrote:
> 
> Hello, this is a small tutorial page about NESL, an easy parallel
> programming language:
> http://www-2.cs.cmu.edu/~scandal/nesl/tutorial2.html
> 
> Its syntax shares some similarities with python one, for example:
> 
> function factorial(n) =
>   if (n <= 1) then 1
>   else n*factorial(n-1);
> 
> {factorial(i) : i in [3, 1, 7]};
> 
> This computes "in parallel, for each i in the sequence [3, 1, 7],
> factorial i"
> 
> 
> {sum(a) : a in [[2,3], [8,3,9], [7]]};
> 
> sum of sequences is already a parallel operation, so this is a nested
> parallelism example.

The look of a language has nothing to do with its parallelizability.  It
just so happens that the designers of NESL had a similar language design
ideas as the designers of Python.


> So it seems to me that Python can be already fit to be interpreted in
> parallel, for multicore CPUs, Playstation Cell-like processors, etc.
> (few things have to be changed/added in the syntax to make it fit for
> parallelism).

There are various other reasons why Python is not as parallelizable as
you would think.  Among them is the semantics of scoping, and whether
there is shared or unshared scope among the processors/nodes.  If shared,
then any operation that could change scopes would need to be distributed
(ick), or if unshared, then you are basically looking at an
automatically distributed tuplespace (LINDA).  It gets even uglier with
certain kinds of generators.

Regardless of which one is the case, heavy modifications to Python would
necessarily need to be done in order to make them happen.


 - Josiah