Re: How to use OpenMP with PARI/GP?

[Erkan Tairi <erkan.tairi@gmail.com>]

Thank you Bill. The fix worked nicely, and your explanation was very helpful.

Cheers,

Erkan

On Thu, Jun 11, 2020 at 11:08 PM Bill Allombert <Bill.Allombert@math.u-bordeaux.fr> wrote:

On Thu, Jun 11, 2020 at 10:44:44PM +0200, Erkan Tairi wrote:
> Hi Bill,
>
> Sorry about that, I updated my question on stackoverflow with the new
> code:
> https://stackoverflow.com/questions/62322277/how-to-use-openmp-with-pari-gp

Thanks!

You can fix it by removing the lines

  for (size_t i = 0; i < numthread; i++) {
    if (&pth[i] != NULL) pari_thread_free(&pth[i]);
  }

I explain: each threads use its own PARI stack to store results.
Calling pari_thread_free destroys the PARI stack thread and any
result computed by that thread.
So whatever result you want to preserve need to be moved to the main
stack using gcopy before calling pari_thread_free.

In fact this is why the API has pari_thread_alloc: to allow the
thread stacks to survive pari_thread_close so that the main thread
get the results.

Cheers,
Bill.