Re: Help running parfor...

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Thu, May 18, 2023 at 04:25:06PM -0500, wraithx@morpheus.net wrote:
> Hello,
> 
> I think I'm having trouble using parfor.  I just downloaded and installed
> Pari64-2-15-3-pthread.exe.  I'm trying to use parfor, but it seems like it
> is only using a single thread.  I've created some test code to use 4
> threads, and it seems to run the first iteration until completion, then it
> starts running the second iteration to completion, and so on until the last
> iteration until completion.  I put in print statements hoping to see it
> randomly working on different iterations, depending on which thread executed
> the print statement. But it's printing each iteration in order with no sign
> of parallelism here.

  parfor(i = first_n, last_n,
    get_fname(p,i),
    fname,
    parallel_g(fname, p, i, range)
  );

When using parfor the first sequence of instructions (3rd arhument, here get_fname(p,i)) is run
in parallel, but not the second one (5th argument, here parallel_g) which is sequentially.
This is on purpose.
So yes, the call to parallel_g are done sequentially in this example.

Maybe you wanted to do simply:

  parfor(i = first_n, last_n,
    my(fname=get_fname(p,i));
    parallel_g(fname, p, i, range)
  );

Beware that on Windows Pari64-2-15-3-pthread.exe might be much slower than Pari64-2-15-3.exe
It is better to use the Windows subsystem for Linux.

Cheers,
Bill.