Thanks for your comments, Dan.

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

My reading of the text of lines 14-18 is to constrain the use of MPI_REQUEST_FREE and nothing else. It so happens that line 21 _implies_ additional restrictions, but these are not stated. And given that line 21 is preceded by "If this rule [pertaining to MPI_REQUEST_FREE] is followed..." it is not unreasonable to interpret line 21 as a non-normative illustration of the rule described in 14-18. Only if one reads line 21 as both normative and itself a constraint on its own (i.e. ignoring its relationship to lines 14-18), does one conclude that starting a request twice without completing it first is prohibited.

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 agree that the constraint on STARTALL follows immediately once it is established for START.

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.

I recall that am one of the very few members of that chapter committee. I will propose changes for the external interfaces chapter that I will then argue in the corresponding chapter committee context are ticket-0 :-) Best, Jeff

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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