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

Sun Apr 5 19:45:42 CDT 2009

Hi,

This sort of puts the argument upon its head. It reads almost like "let's define a standard as we please, and those who don't like it may not upgrade". I bet there will be some who won't, as currently MPI-2.2 does not seem to provide an overwhelming set of new features to justify ABI incompatibility. What's the point in defining such a standard?

I'm about to propose to scuttle an ABI-incompatible MPI-2.2 altogether then. Let's collect a critical mass of new features in the MPI-3, and then we'll be able to fix ABI issues in due order.

Full disclaimer: written upon a 10-hour flight, running into 3 am by the old time zone.

Best regards.

Alexander 

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Jeff Squyres
Sent: Saturday, April 04, 2009 3:54 PM
To: MPI 2.2
Subject: Re: [Mpi-22] [MPI Forum] #59: Clarification on MPI::FILE_NULL, MPI::WIN_NULL and MPI::COMM_NULL

Regardless of this point, note that the C++ bindings are *broken* in  
MPI-2.1 with regards to #55.  You can't compile C++ MPI-2.1  
applications that use MPI::FILE_NULL, MPI::WIN_NULL as specified in  
#55, so the point may be moot for this ticket.

But the general point may need broad discussion next week -- have we  
been sure to adhere to the "must be ABI compatible" rule for all  
MPI-2.2 issues?

My $0.02: why would ISV's (or any MPI application provider) upgrade to  
an MPI-2.2 implementation?  They would only upgrade if there are  
features or bug fixes that they want.  They would not upgrade for the  
sake of upgrading to 2.2.  In such cases, I think it's ok for any MPI  
application developer (ISV or not) to re-compile.  Indeed, most ISV's  
bundle/ship their own MPI implementation, so they tightly control the  
MPI anyway.  If they don't want to upgrade to an MPI-2.2  
implementation, they won't.

On Apr 3, 2009, at 4:04 PM, Supalov, Alexander wrote:

> 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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-- 
Jeff Squyres
Cisco Systems
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