[m-rev.] for review: Separate processor counting from thread pinning.

[Peter Wang]

On Tue, 24 Jun 2014 19:45:43 +1000, Paul Bone <paul at bone.id.au> wrote:
> On Tue, Jun 24, 2014 at 12:22:27PM +1000, Julien Fischer wrote:
> >
> > On Mon, 23 Jun 2014, Peter Wang wrote:
> >
> >> Branches: master, 14.01
> >>
> >> In low-level C parallel grades we need the number MR_num_processors to
> >> prime MR_num_threads when it is not explicitly set by the user, even if
> >> thread pinning support is not available.
> >
> > BTW, can you add a brief entry to the 14.01.1 NEWS about this.
> 
> I thought this worked already, maybe it didn't fill out MR_num_threads
> properly but it did create the correct number of Mercury engines.

A quick grep will reveal that MR_num_threads is set in only two places:
in MR_setup_thread_pinning, and in response to MERCURY_OPTIONS=-Pn.
If MR_num_threads stays at its initial value of zero, it crashes due to
division by zero while creating the engine for the primordial thread:

    eng->MR_eng_victim_counter = (eng->MR_eng_id + 1) % MR_num_threads;

Peter