[Mpi-22] MPI_INIT assertions

Mon May 5 16:53:05 CDT 2008

I changed the subject to be meaningful - it had been  "Re: [Mpi-22] mpi-22
Digest, Vol 2, Issue 7"

I do think this proposal is within the scope of the MPI 2.2 rules so I am
pleased to hear this is being considered.

I am 100% convinced that a query function should be part of this proposal,
probably with 2 query flavors. One flavor of the query would respond with
the set of assertions the application MPI_INIT_xxx call had provided and
another would respond with the set of assertions the MPI implementation is
actually exploiting.

One library author may decide he will use if/else logic based on how the
MPI implementation will behave. The application may assert MPI_NO_yyy but
if the MPI implementation does not exploit MPI_NO_yyy then the library can
still use the code that depends on yyy. Another library author may depend
unconditionally on yyy.  On an MPI implementation that does not exploit
MPI_NO_yyy he may want to issue a warning that assertion MPI_NO_yyy is
non-portable but let the job run. On one that does exploit MPI_NO_yyy he
would abort the job. Or, he may decide to simply abort any job that asserts
MPI_NO_yyy to avoid having the library suddenly quit working when the
customer upgrades to an MPI implementation that does exploit MPI_NO_yyy.

I think 32 assertions is probably more than enough

Even a handful of defined assertions can raise testing costs. For simple
cases like MPI_NO_ANY_SOURCE it is easy for a user  to judge whether a
piece of code is OK but if we begin to add subtle or narrow semantic
assertions it gets harder. Some library providers will be tempted to say "I
cannot proof read and test my code to a degree that will allow me to accept
28 specific assertions and forbid 4. I will simply forbid every subtle
assertion I cannot afford to test."

I predict that for large applications developed by teams and for community
open source efforts the design leads will consider requiring that all parts
be written to live within a few carefully chosen assertions. The design
leads will not want to provide a list of 26 subtle or narrow assertions and
require that everyone respect all 26 in the code they contribute.

Many distinct assertions also could become a big test cost for MPI
implementors and customers who must qualify an MPI implementation before
trusting their business to it.  If there were 64 or more assertions, how
would a tester decide what combinations of assertions must be tested and
then create suitable test cases?

        Dick

Dick Treumann  -  MPI Team/TCEM
IBM Systems & Technology Group
Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
Tele (845) 433-7846         Fax (845) 433-8363

mpi-22-bounces_at_[hidden] wrote on 05/05/2008 01:28:06 PM:

> Dear Dick,
>
> Thank you. We can actually introduce what you propose, possibly with
> a query function to make it still easier to live with, as early as
> in MPI 2.2, as a subset precursor. Judging by the discussion in
> Chicago, subsets may not need much more than that in the end,
> possibly with a little more flags and semantics added in MPI-3.
>
> The reservation against 32- (or for that matter, 64-) bit limitation
> is the only one I have at the moment. Not being able to attach
> assertions to communicators, etc. may be missed by some advanced
> programmers, but here we need to be pragmatic: who will ever want to
> go that deep?
>
> Best regards.
>
> Alexander
>
> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
> bounces_at_[hidden]] On Behalf Of Richard Treumann
> Sent: Monday, May 05, 2008 7:18 PM
> To: MPI 2.2
> Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7

> Hi Alexander
>
> I have no objection to citing my "assertions" proposal in the
> subsetting discussions. I do want to keep it clear that this
> proposal is intended to be as simple as practical to implement, exploit
and
> live with.
>
> "Live with" applies to 3rd party library authors or anyone else who
> must write MPI code but does not know and control the structure of
> the entire application. That guy must "live with" the decisions made
> by whoever coded the MPI_INIT piece. "Live with" also applies to
> whoever must test or certify a specific MPI implementation.
>
> Thanks - Dick
>
> Dick Treumann - MPI Team/TCEM
> IBM Systems & Technology Group
> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
> Tele (845) 433-7846 Fax (845) 433-8363
>
> [image removed] "Supalov, Alexander" <alexander.supalov_at_[hidden]>
>

>
> "Supalov, Alexander" <alexander.supalov_at_[hidden]>
> Sent by: mpi-22-bounces_at_[hidden]
> 04/26/2008 04:03 AM
>
> Please respond to
> "MPI 2.2" <mpi-22_at_[hidden]>
>
> [image removed]
> To
>
> [image removed]
> "MPI 2.2" <mpi-22_at_[hidden]>
>
> [image removed]
> cc
>
> [image removed]
>
> [image removed]
> Subject
>
> [image removed]
> Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7
>
> [image removed]
>
> [image removed]
>
>
> Dear Dick,
>
> Thank you. Would you mind if I cite your proposal in the subsets
> discussion? Yours looks like a good alternative to the thinking of
> some of us that subsets might be very rich and mutable, and to
> Jeff's proposal on hints I've already cited there with his permission.
>
> Best regards.
>
> Alexander
>
> From: mpi-22-bounces_at_[hidden] [mailto:mpi-22-
> bounces_at_[hidden]] On Behalf Of Richard Treumann
> Sent: Thursday, April 24, 2008 6:16 PM
> To: MPI 2.2
> Subject: Re: [Mpi-22] mpi-22 Digest, Vol 2, Issue 7
> Dick Treumann - MPI Team/TCEM
> IBM Systems & Technology Group
> Dept 0lva / MS P963 -- 2455 South Road -- Poughkeepsie, NY 12601
> Tele (845) 433-7846 Fax (845) 433-8363
>
>
> mpi-22-bounces_at_[hidden] wrote on 04/24/2008 11:33:42 AM:
>
> > Hi,
> >
> > Note that this is an argument for making the assertions optional: those
> > who don't care don't have to use them. Those who care should use them
> > correctly or else. As usual.
> >
> > Best regards.
> >
> > Alexander
> >
>
> Hi Alexander
>
> The assertions are optional in this proposal.  If this is added to
> the MPI standard the minimal impacts (day one impacts) are:
>
> ==
> To application writers (none) - MPI_INIT and MPI_INIT_THREAD still
> work. MPI_INIT_THREAD_xxx can be
> passed 0 (zero) as the assertions bit vector.
>
> To MPI Implementors (small) - subroutine MPI_INIT_THREAD_xxx can be
> a clone of MPI_INIT_THREAD under the covers. If the Forum decides
> the query function is for asking what assertions are being honored,
> the implementation can just return "none" to every query. If there
> is also a query for what assertions have been made then there are a
> few more lines of code the implementor must write to preserve the
> value so it can be returned(maybe 10 lines)
>
> Writers of opaque libraries (small) - call the query function at
> library init time and if any assertions are found, issue an error
> message and kill the job. This is awkward for a library that wants
> to support every MPI whether it has implemented the new query function or
not.
> ==
>
> As MPI implementations begin to take advantage of assertions there
> is more work for the MPI implementor and the library author must
> begin to think about whether his customer will be upset if the
> library simply outlaws all assertions.
>
> The library author will never be wrong if he simply forbids
> assertions forever. If they become valuable he will feel the
> pressure to work it out.
>
> The MPI implementor will never be wrong if he adds the API but
> simply ignores assertions forever. If they become valuable he will
> feel the pressure to honor some at least.
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