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

Underwood, Keith D keith.d.underwood at [hidden]
Fri Mar 13 11:46:34 CDT 2009 


Yes, you have to cast it away for Portals and Elan (http://web1.quadrics.com/downloads/documentation/ElanProgMan_5.3.pdf)

Keith

>-----Original Message-----
>From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-bounces_at_lists.mpi-
>forum.org] On Behalf Of Jeff Squyres
>Sent: Friday, March 13, 2009 7:05 AM
>To: MPI 2.2
>Subject: Re: [Mpi-22] Ticket #46: Addconst Keyword to the C bindings-
>implementation
>
>Do you end up casting away the const when invoking the Windows network
>interfaces?
>
>On Linux, I think the following interfaces would require casting the
>const away:
>
>- shared memory (even using Linux vmsplice())
>- MX
>- TCP
>- OpenFabrics (both verbs and udapl)
>
>These interfaces do not require casting away const:
>
>- SCTP (I *think* -- I'm not an SCTP expert, but a quick look in
>sctp.h showed a "const" argument for the sctp_sendmsg() function)
>
>I can't check these offhand:
>
>- Portals
>- Elan
>
>
>
>On Mar 12, 2009, at 6:06 PM, Erez Haba wrote:
>
>> I urge you, please read the ticket proposal again. It discusses the
>> merit of this proposal.
>>
>> As for IB; yes you'd copy small messages (which const is fine with)
>> and some implement RDMA read or write for large messages; you might
>> need to cast the const away if your IB interface does not expose
>> const SGE's.
>>
>> As for the compiler; no you are not violating the contact;
>> (otherwise we wouldn't have casts); as long as you guarantee that
>> you are not changing the buffer. It's a way for the programmer to
>> use old, non const correct, interfaces.
>>
>> .Erez
>>
>> -----Original Message-----
>> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>bounces_at_[hidden]
>> ] On Behalf Of Underwood, Keith D
>> Sent: Thursday, March 12, 2009 2:03 PM
>> To: MPI 2.2
>> Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings- implementation
>>
>> I didn't think that typical MPI implementations over IB copied the
>> data for large messages (as opposed to the bounce buffers for small
>> messages).
>>
>> If you are going to have to cast away the const, what is the point
>> of putting it in?  In fact, if you have to cast away the const,
>> aren't you violating your contract with the compiler?  Should this
>> change be rolled out from the bottom up?  i.e. common low-level APIs
>> first and then MPI?
>>
>> Keith
>>
>> >-----Original Message-----
>> >From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>bounces_at_lists.mpi-
>> >forum.org] On Behalf Of Erez Haba
>> >Sent: Thursday, March 12, 2009 2:10 PM
>> >To: MPI 2.2
>> >Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings-
>> >implementation
>> >
>> >Possibly you'll have to cast.
>> >There are few interfaces that take const for send buffer (like
>> sockets).
>> >In other cases you copy the buffer (like with IB) which keeps the
>> const
>> >property.
>> >
>> >Thanks,
>> >.Erez
>> >
>> >-----Original Message-----
>> >From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>bounces_at_lists.mpi-
>> >forum.org] On Behalf Of Underwood, Keith D
>> >Sent: Thursday, March 12, 2009 12:05 PM
>> >To: MPI 2.2
>> >Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings-
>> >implementation
>> >
>> >It would seem like const would eventually have to be cast away for
>> most
>> >lower level interfaces.  Portals, Elan, IB Verbs, and as best I can
>> tell MX
>> >don't have const on their send buffers...
>> >
>> >Keith
>> >
>> >>-----Original Message-----
>> >>From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>bounces_at_lists.mpi-
>> >>forum.org] On Behalf Of Erez Haba
>> >>Sent: Thursday, March 12, 2009 12:44 PM
>> >>To: MPI 2.2
>> >>Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings-
>> >>implementation
>> >>
>> >>No, it's not being cast away (although it is a quick way for you to
>> >>implement it).
>> >>In MPICH2 implementation it trickles down to the lower functions.
>> There
>> >are
>> >>very few places where the const is being cast away because ticket
>> #46 does
>> >>not to break backward compatibility.
>> >>For example, when the user function is called (const was not added
>> to the
>> >>MPI_User_function) the implementation must cast away const from
>> the send
>> >>buffer before calling the user function.
>> >>
>> >>Thanks,
>> >>.Erez
>> >>
>> >>-----Original Message-----
>> >>From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>bounces_at_lists.mpi-
>> >>forum.org] On Behalf Of Jeff Squyres
>> >>Sent: Thursday, March 12, 2009 11:34 AM
>> >>To: MPI 2.2
>> >>Subject: Re: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings-
>> >>implementation
>> >>
>> >>More importantly, how is const handled?  Is it just cast away inside
>> >>the MPI library?
>> >>
>> >>
>> >>On Mar 12, 2009, at 2:34 PM, Underwood, Keith D wrote:
>> >>
>> >>> Since the main purpose of an implementation for something like
>> >>> adding const is to see how invasive the change is, would it be
>> >>> possible to get a diff against the trees that these were created
>> from?
>> >>>
>> >>> Thanks,
>> >>> Keith
>> >>>
>> >>> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
>> >>bounces_at_[hidden]
>> >>> ] On Behalf Of Erez Haba
>> >>> Sent: Thursday, March 12, 2009 12:24 PM
>> >>> To: MPI 2.2
>> >>> Subject: [Mpi-22] Ticket #46: Add const Keyword to the C
>> bindings -
>> >>> implementation
>> >>>
>> >>>
>> >>> Implementation for ticket #46 is now available from ANL (thanks
>> Pavan)
>> >>>
>> >>>
>> >>> tarballs
>> >>>
>>
>>>http://www.mcs.anl.gov/research/projects/mpich2/downloads/tarballs/nightl
>y
>> >/
>> >>const
>> >>>
>> >>>
>> >>> thanks,
>> >>> .Erez
>> >>>
>> >>> _______________________________________________
>> >>> mpi-22 mailing list
>> >>> mpi-22_at_[hidden]
>> >>> http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-22
>> >>
>> >>
>> >>--
>> >>Jeff Squyres
>> >>Cisco Systems
>> >>
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>> >>
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>
>--
>Jeff Squyres
>Cisco Systems
>
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