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Subject: Re: [OMPI devel] RFC: make hwloc be a 1st-class citizen
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2011-09-12 09:55:13


OPAL_HAVE_HWLOC will always be defined to 0 or 1.

On Sep 12, 2011, at 9:46 AM, Kenneth Lloyd wrote:

> According to http://gcc.gnu.org/onlinedocs/cpp/If.html
>
> "The `#if' directive allows you to test the value of an arithmetic
> expression, rather than the mere existence of one macro."
>
> Is the objective to test for the existence of the macro, its value, or its
> value IFF it exists?
>
> Ken Lloyd
>
> -----Original Message-----
> From: devel-bounces_at_[hidden] [mailto:devel-bounces_at_[hidden]] On
> Behalf Of Jeff Squyres
> Sent: Monday, September 12, 2011 7:07 AM
> To: Open MPI Developers
> Subject: Re: [OMPI devel] RFC: make hwloc be a 1st-class citizen
>
> On Sep 12, 2011, at 8:51 AM, Jeff Squyres wrote:
>
>> *** Remember that although the opal_hwloc_topology global variable will
> always be available, ##IT MAY BE NULL## on platforms where hwloc was
> compiled out / not supported. Therefore, you MUST protect access to hwloc
> API calls with #if OPAL_HAVE_HWLOC! See the original RFC text below.
>
> Oops! Ralph just reminded me that this was slightly inaccurate.
>
> If hwloc is not present, then the global variable opal_hwloc_topology won't
> be present at all (because its corresponding hwloc type won't be available).
> Hence, the example in the original RFC isn't quite right:
>
>>> if (NULL != opal_hwloc_topology) {
>>> #if OPAL_HAVE_HWLOC
>>> // ...use hwloc API, etc.
>>> #endif
>>> }
>
> This really should be:
>
> #if OPAL_HAVE_HWLOC
> if (NULL != opal_hwloc_topology) {
> // ...use hwloc API, etc.
> }
> #endif
>
> Sorry for the confusion!
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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-- 
Jeff Squyres
jsquyres_at_[hidden]
For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/