simple parallelization

[Max Alekseyev <maxale@gmail.com>]

Dear pari-developers,

Would it be possible to implement an optional threading that would
automatically parallelize execution of any for*/sum*/vector/matrix
loops (i.e. all loops with predetermined number of iterations)? I mean
something like

default( threads, 4 );
vector( 100, i, f(i));

which would run the 'vector' loop in four threads, each with its own
value of i and computing its own f(i).

Of course, not every loop is parallelizable this way but this feature
would be off by default (threads = 1) and the user will take
responsibility for code's correctness (independence of iterations,
order of output, or whatever other related issues) when threading is
on. Moreover, it would be possible to turn threading on and off as
needed within a single program.

Personally, in many cases I have independent loop iterations that may
easily run in parallel (say, on 4 cores) but currently I can do
parallezation only either by explicitly by running several PARI/GP's
in parallel or by writing C code using pari library and threading,
which is rather inconvenient and troublesome.
The proposed approach appears to me rather universal and may greatly
simplify parallelization with PARI/GP.

Regards,
Max