[Mpi-22] [MPI Forum] #59: Clarification on MPI::FILE_NULL, MPI::WIN_NULL and MPI::COMM_NULL

[Supalov, Alexander]

Right. This is why I'm not sure whether changing the const status may break existing apps: only compiler writers know for sure what kind of repercussions this change may have in a C++ program. We should probably ask them, at least in order to make data based decisions.

Semantic changes are also important and should be reduced only to clean extensions. If an application expects a certain outcome, and this outcome changes, the application may break, defeating MPI-2.2 charter.

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba
Sent: Friday, April 03, 2009 9:58 PM
To: MPI 2.2
Subject: Re: [Mpi-22] [MPI Forum] #59: Clarification on MPI::FILE_NULL, MPI::WIN_NULL and MPI::COMM_NULL

I think it's both;
Any compiled application that is running against any specific implementation does not have to recompile/rebuild to continue and run against an updated implementation that is compliant with MPI 2.2.
i.e., MPI 2.2 does not mandate any runtime incompatibility. An example for such incompatibility would be to for a change of the rank parameter from int to MPI_Aint.

Plus - any application that recompiles with the new MPI 2.2 headers should not incur any (new) compiler errors.

The first rule is significant to ISV's that release binary implementation. Without this requirement, MPI 2.2 would create a significant backward compatibility to those implementing.

Thanks,
.Erez
-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Jeff Squyres
Sent: Friday, April 03, 2009 11:07 AM
To: MPI Forum
Subject: Re: [Mpi-22] [MPI Forum] #59: Clarification on MPI::FILE_NULL, MPI::WIN_NULL and MPI::COMM_NULL

This is worth raising to the list.

What is the rule for 2.2 -- that existing MPI applications must be  
able to run with no changes against an MPI-2.2 library?  Or is it that  
existing MPI applications must be able to compile and run with no  
source code changes against an MPI-2.2 implementation?

I hope it's the latter; this change is relatively important.

On Apr 3, 2009, at 5:56 AM, MPI Forum wrote:

> #59: Clarification on MPI::FILE_NULL, MPI::WIN_NULL and MPI::COMM_NULL
> ----------------------------------- 
> +----------------------------------------
> Reporter:  hubertritzdorf          |            Owner:  hubertritzdorf
>     Type:  Correction to standard  |           Status:  new
> Priority:  Waiting for reviews     |        Milestone:  2009/04/06  
> Chicago
>  Version:  MPI 2.2                 |       Resolution:
> Keywords:                          |   Implementation:  Completed
> ----------------------------------- 
> +----------------------------------------
> Changes (by asupalov):
>
>  * cc: alexander.supalov_at_[hidden] (added)
>
>
> Comment:
>
>  Aren't we changing C++ ABI herewith? If so, we may want to postpone  
> this
>  change till MPI-3.
>
> --
> Ticket URL: <https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/59#comment:33 
> >
> MPI Forum <https://svn.mpi-forum.org/>
> MPI Forum


-- 
Jeff Squyres
Cisco Systems
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