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

Tue Mar 17 18:20:06 CDT 2009

Okay, following your logic I would say that the MPI C++ binding makes the MPI C bindings obsolete because it uses the const modifier at the C++ level where it's not at the MPI C level. (The MPI C++ implementation is using the C bindings)

Does this follow your logic correctly?

Thanks,
.Erez

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander
Sent: Tuesday, March 17, 2009 1:05 AM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Thanks. Then I have to disagree for the reasons mentioned below. In my view, adding the const modifier at the MPI level does add to the obsolescence down below by basically forcing the lower level interfaces move toward the use of the const keyword, what they currently and predominantly do not do.

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba
Sent: Monday, March 16, 2009 10:48 PM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

It means that adding the const keyword is not relevant to the obsoleteness of the lower level interface (ticket #45 is).

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander
Sent: Monday, March 16, 2009 2:37 PM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Thanks. What does it mean here, "more "obsolete" or less "obsolete""? Did you mean "more "obsolete" or less "advanced""?

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba
Sent: Monday, March 16, 2009 6:22 PM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Yes, I think we agree. Let me rephrase.

With ticket #45 (send buffer access) being accepted, adding the const keyword does make any network interface more "obsolete" or less "obsolete".

Thanks,
.Erez

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander
Sent: Monday, March 16, 2009 4:22 AM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Dear Erez,

Thanks. Before this becomes too involved, let's untangle this a little.

There are three topics here:

1. The send buffer change (#45).
2. The const pointer modifier (#46).
3. Bill's claim that 2. "simply captures the previously required semantics of the interface in the syntax".

My message contained two statements:

A. I said that 2. can only be understood in relation to 1. rather than the existing standard (say, MPI 2.1). I doubt this can be refuted. The old standard did allow in-place buffer changes. This would be impossible with the const buffer modifier. Hence my statement.

B. Now, at least for me, 2. simply seals 1. This is why I said that this will make interfaces "obsolete". You object to this. Here's my reasoning: if I have to cast the const away on a lower level interface to make use of the MPI buffer, I surely have an issue. The issue is that the new MPI interface advanced ahead of my lower level networking interface. Thus, from the point of view of the MPI interface, the respective lower level interface becomes "obsolete". Hence my claim and hence the quotes - to point out that this is only MPI POV. Note that this is, in essence, only a negative rewording of Bill's "MPI should take the lead" clause. I doubt this can be refuted either.

Finally, you added that 1. makes some networking interfaces "obsolete". Taking into account A. and B. above, I think we're in violent agreement: both 1. and 2. make MPI lead, or, in other words, make many networking interfaces "obsolete" from the MPI POV. This is very brave on part of the MPI standard. Let's see what happens next.

Best regards.

Alexander

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Erez Haba
Sent: Monday, March 16, 2009 11:53 AM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Dear Alexander,

Your claim that the const keyword might render some internal networking interfaces as "obsolete" is not correct. The const keyword has no effect on how relevant the network interface is. You probably mean that ticket #45 (send buffer) might render these interfaces as obsolete, and that would be a correct claim for those network interfaces that modify the send buffer.

Thanks,
.Erez

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of Supalov, Alexander
Sent: Monday, March 16, 2009 3:43 AM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Hi,

I most respectively disagree with the "Const simply captures the previously required semantics of the interface in the syntax" statement. The standard did not prohibit a reversible in-place modification of the send buffer until the very recent change related to #45. Adding const on top will automatically make MPI not the greatest common denominator - some internal networking interfaces that were mentioned in this trail will suddenly become "obsolete". That is, most of the existing networking interfaces will.

Best regards.

Alexander

-----Original Message-----
From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_[hidden]] On Behalf Of William Gropp
Sent: Sunday, March 15, 2009 9:59 PM
To: MPI 2.2
Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C bindings-implementation

Actually, MPI has taken the lead in a number of areas, including cross- 
language compatibility, to say nothing of the existence of MPI itself.

And MPI has taken great pains to be the *greatest* common  
denominator.  Const simply captures the previously required semantics  
of the interface in the syntax, and is consistent with the MPI spirit.

Bill
On Mar 13, 2009, at 2:17 PM, Jeff Squyres wrote:

> On Mar 13, 2009, at 9:40 AM, William Gropp wrote:
>
>> First, this is a chicken-and-egg problem; the low level
>> interfaces are unlikely to change to add const unless there is some
>> application that will take advantage of that (and internally, if  
>> their
>> semantics allows it and their compiler can support it, they'll just
>> cast to add the const).  So MPI should take the lead, particularly
>> since using const also provides information to the user.
>>
>
> This is a very scary statement to me.  MPI has not traditionally
> "taken the lead" on forcing issues with other interfaces (look where
> it has gotten us with Fortran...).  Indeed, MPI has taken great pains
> to be the lowest common denominator across a variety of language,
> platforms, and operating systems.
>
> -- 
> Jeff Squyres
> Cisco Systems
>
> _______________________________________________
> mpi-22 mailing list
> mpi-22_at_[hidden]
> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22

William Gropp
Deputy Director for Research
Institute for Advanced Computing Applications and Technologies
Paul and Cynthia Saylor Professor of Computer Science
University of Illinois Urbana-Champaign

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