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Subject: Re: [hwloc-devel] -lhwloc in components.
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-09-05 11:40:07


I agree -- all of the things you mention are do-able.

But it's a whole lot more bookkeeping and care/feeding to ensure that nothing goes wrong vs. just calling a hwloc core function and assuming it's there. Such things will require maintenance over time.

In the end -- it's a tradeoff:

- do we want the maintenance associated with a struct full of core function pointers?

or

- do we want to use the solution I mentioned in http://www.open-mpi.org/community/lists/hwloc-devel/2012/09/3253.php?

Both have strengths / weaknesses.

On Sep 5, 2012, at 11:25 AM, Samuel Thibault wrote:

> Jeff Squyres, le Wed 05 Sep 2012 17:13:56 +0200, a écrit :
>>> The source code shouldn't need to be modified:
>>>
>>> #define hwloc_foo_bar(arg1, arg2) hwloc_funcs->foo_bar(arg1, arg2)
>>
>> You need to make sure that #define is only effected in certain places in the code.
>
> Well, all the places that will constitute a plugin, no?
>
>> And you need to ensure that hwloc_funcs->[foo] isn't attempted to be used before it has been filled in.
>
> As I said in my earlier mail, hwloc_funcs would be provided by the
> loader of the plugin, so it can make sure it's filled in (I forgot to
> mention that what I call hwloc_funcs above is an internal variable of
> the plugin, not a symbol provided by libhwloc.so).
>
>> And unless there is a very fixed set of functions that can be called by plugins,
>
> Well, I believe we'll have to have that anyway. That was part of the
> whole discussion about plugins a long time ago.
>
>> you'll probably need to grow hwloc_funcs over time, which may lead to ABI issues...?
>
> Sure. We can for instance make the plugin check for the size of
> hwloc_funcs provided by the plugin loader vs the size that it was
> compiled against, and thus refuse to get loaded by an older hwloc.
>
> Samuel
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-- 
Jeff Squyres
jsquyres_at_[hidden]
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