itaps-parallel Two options from today's iMeshP phone conference

[Jason Kraftcheck]

Mark Beall wrote:
> 
> On Jul 19, 2010, at 1:06 PM, Jason Kraftcheck wrote:
> 
>> Mark Beall wrote:
>>
>>>
>>> Would it make sense for an implementation to define a value that means
>>> NULL (for here and other places that it could be of use)?
>>
>> Well, what value would you choose and how would you guarantee that it
>> wouldn't be problematic for any existing implementation?  Zero would
>> clearly
>> be troubling for an implementation that was array-based and simply used
>> array indices as handles.
> 
> There could be a function that returns that value (iMesh_getNullSet) or

We could do that.  But it seems a lot simpler to use the existing
iMesh_getRootSEt.

> a global that the implementation must initialize to that value.
> 

This would definitely eliminate the possibility of ever using multiple
implementations at the same time.


>>> Passing the
>>> root set here could be confusing ("ah I see, everything is always added
>>> to the root set since I always have to pass it here. Oh wait, sometimes
>>> I don't have to pass it here, does that mean that this entity won't be
>>> added to the root set?")
>>>
>>
>> I think this was one of the reasons that Tim argued that the function
>> accept
>> any set in the serial case.  It would be less confusing than
>> documenting a
>> special case where an app need always pass the same redundant value (when
>> working in serial.)
> 
> The problem with accepting any set is that you don't want people to use
> it for some other purpose in serial and then find they have to change
> their code to do the right thing in parallel.
> 
>> I suppose we could pass a pointer to the handle, such that the pointer
>> could
>> be NULL.  I'm not sure that that would be any less confusing than
>> using the
>> root set, through.  And we already use the root set handle in exactly the
>> same way in iMesh_loadMesh.
> 
> I'd say that using the root set to mean both "no set" and "the set that
> contains everything" is confusing. In iMesh_loadMesh (and most other
> places I saw when I looked quickly) you can say that it means
> "everything in the instance", which is the same as the root set. However
> if there are places (now or in the future) where there is a meaningful
> difference between the two things, that usage could become problematic.
> 

How does it mean 'the set that contains everything' in the *load*Mesh case?

-jason