[mpiwg-p2p] how to classify ticket 471 ("MPI_START(ALL) restrictions")?

Dan Holmes dholmes at staffmail.ed.ac.uk
Fri Jan 16 11:37:35 CST 2015

Hi Jeff,

MPI 3.0 p78 lines 18-25 (section 3.9) forces the correct sequence and 
explicitly calls out the case of multiple concurrent threads.

Also, a MPI_STARTALL call "has the same effect as" lots of MPI_START 
calls "in some arbitrary order" p78 lines 5-7 plus "the request should 
be inactive... becomes active once the call is made" p77 lines 28-29 so 
specifying a request more than once in the vector to MPI_STARTALL is 
pretty much guaranteed to break the correct sequence and the 
chronologically second implied MPI_START will be supplied with an active 
request, which is defined to be bad.

I think that section 3.9 is fine and deals with all your points of 
possible ambiguity. Section 12 then incorrectly tries to un-write some 
of those rules by absent-mindedly neglecting the existence of persistent 
requests. Changing the text you quote (section 12.4.3), in particular 
"In MPI, a request can only be completed once" - *buzzz*, fail - is, 
IMHO, errata because the Standard is semantically (rather than just 
syntactically) wrong and needs to be corrected. Determining ticket-0 on 
this is a matter for the External Interfaces chapter committee. An 
errata could be brought by this WG because it is point-to-point 
functionality that is causing the conflict or by the Hybrid WG because 
it is all the fault of those pesky threads again.


On 16/01/2015 17:00, Jeff Hammond wrote:
> I created https://svn.mpi-forum.org/trac/mpi-forum-web/ticket/471 last
> night.  Jim and Sayantan the overall concept is noncontroversial.
> Is this ticket-0, an errata, or something that has to be read for MPI-4?
> Thanks,
> Jeff

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