From: Douglas Gregor <dgregor@XXXXXXXXXX>
Date: January 9, 2008 4:19:15 PM CST
To: mpi-21@XXXXXXXXXXXXX
Subject: RE: [mpi-21] Proposal EH2: add const keyword to the C bindings
Reply-To: mpi-21@XXXXXXXXXXXXX


On Wed, 2008-01-09 at 13:51 -0800, Bronis R. de Supinski wrote:
> Dick:
>
> Re:
>> I think it is likely the forum will conclude that the send buffer  
>> access
>> rules should be relaxed but there should be more to the discussion  
>> than
>> "Do you care about users or don't you?"

> I have implemented a lot of MPI code. I work with many
> serious MPI application and library programmers. I have
> implemented tools that detect MPI programming errors.
> I have several people who use that tool and find it
> helpful. I have read many papers on the subject of MPI
> coding errors. I have seen some pretty bizarre MPI errors.

Do the tools you mentioned check for this particular error? If not, then
I don't see how they factor into this discussion.


> Not ONCE have I heard that "Restricted access to buffers
> of non-blocking MPI send operations was the source of my
> problem." Not only do implementations not take advantage
> of the opportunity, the restriction is NOT violated.

I don't understand how you came to the conclusion that this restriction
is not violated, unless some of the tools you mentioned do this check
explicitly.

Most implementations do not take advantage of their ability to change
the contents of the send buffer, therefore even if existing applications
violated this restriction, it is unlikely that we would know it.

An example: I just found some places in my own code where I violate this
restriction, and this code has not failed on LAM/MPI, Open MPI, MPICH,
MPICH2, MVAPICH, MS-MPI, Sun's MPI, or IBM's MPI.

> This
> issue is not worth the time it is being given until someone
> can do more than state that it must be causing problems for
> "many applications and commercial applications." I see no
> reason to sacrifice any potential performance for something
> no one slips on.

Well, now you know that at least one person slipped on it.

   - Doug