[Mpi-22] Ticket #46: Add const Keyword to the Cbindings-implementation

[Darius Buntinas]

Sorry Jeff, I didn't think I was rushing anything.  I'm not saying we
shouldn't put it off till 3.0, but I was challenging the lack of const
qualifiers on low-level interfaces as a reason to do so.

For the record, I do think that the fact that it would require
significant changes in the Open MPI implementation is a legitimate
reason to consider postponing this to 3.0.  But we shouldn't wait till
POSIX changes writev to use const qualifiers.

I wasn't at the last forum meeting, so maybe I missed discussion on
this.  So if I'm missing some context, I apologize.  I'm not trying to
rush this into 2.2, but I guess I'm not in a rush to push it off to 3.0
either.

-d

On 03/18/2009 08:24 PM, Jeff Squyres wrote:
> Can someone explain what the rush is to do this for 2.2?
> 
> Is there a problem with putting this issue off until 3.0?
> 
> 
> 
> On Mar 18, 2009, at 9:15 PM, Darius Buntinas wrote:
> 
>>
>> I just want to point out that casting away the const for low-level
>> interfaces is really a non issue.  Putting a const on the send buffer
>> parameter in an MPI function prototype indicates a contract with the
>> user that the MPI implementation will not change the contents of the
>> buffer referenced from that function.  As long as the MPI implementor
>> knows that a routine called by the library will not modify the buffer
>> it's OK to cast away the const.  E.g., the POSIX standard tells you that
>> writev must not change the contents of the buffer, so casting away const
>> is fine.
>>
>> Sure, that means that the MPI implementor has to be more careful when
>> casting away const to ensure that the function being called won't modify
>> the buffer.   But the whole point of the proposal is so that the
>> _MPI_user_ doesn't need to do this and instead can count on the compiler
>> to do the check.
>>
>> -d
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> 
>