[Mpi-forum] [EXTERNAL] Wording in MPI standard

Jeff Hammond jhammond at alcf.anl.gov
Tue Nov 27 09:15:07 CST 2012

There's a lot of ambiguity in the definitions of these words in
different contexts.  If the MPI Forum wants "should" to mean "is
required to", then such a definition should be explicit in the text.

>From http://en.wikipedia.org/wiki/Shall_and_will#Technical_specifications:

"The IETF (Internet Engineering Task Force) defines shall and must as
synonymous terms denoting absolute requirements, and should as
denoting a somewhat flexible requirement, in RFC documents."


On Tue, Nov 27, 2012 at 9:48 AM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:
> If you search for the word "should" in the document, it is used all over the place. And it does not mean "maybe"
> http://dictionary.reference.com/browse/should?s=t
> Rajeev
> On Nov 27, 2012, at 8:23 AM, Pavan Balaji wrote:
>> On 11/27/2012 04:48 AM US Central Time, Jeff Hammond wrote:
>>> Is it explicitly defined anywhere that "foo has been started" means
>>> "MPI_I*foo has been called by the appropriate MPI rank" or "sufficient
>>> matching has occurred such that foo can proceed without additional
>>> explicit remote activity"?  Perhaps this text would be more clear if
>>> it were more pedantic in this respect, assuming either of my
>>> equivalences are correct.
>> I think this needs to be clarified -- I always tell people that it needs
>> to be matched (even though the standard says it should have "started" --
>> what does that mean, if matching has started, but not completed, is it
>> considered "started").
>>> As for language, while "should" isn't legally enforceable in the same
>>> way that "must" or "shall" are, the MPI standard is not a legally
>>> binding document and I don't think any MPI implementer wants to be
>>> known as the jerk that exploits this loophole to create a formally
>>> standard-compliant implementation that screws over users by violating
>>> the principle of least surprise in important use cases such as Scott's
>>> example.
>> I have to agree with Scott here -- "must" or "is required to be" is a
>> clearer way to describe it.
>> -- Pavan
>> --
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
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Jeff Hammond
Argonne Leadership Computing Facility
University of Chicago Computation Institute
jhammond at alcf.anl.gov / (630) 252-5381

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