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

[Brightwell, Ronald]

The issue is not whether the local non-blocking operation will complete, but whether starting a local non-blocking operation is enough to satisfy the matching non-local operation. It  is essentially saying that once an operation has been started and matched, completion is local. That is, completion of a send operation that has been started and satisfied by a matching receive operation (that has also been started) is not dependent on whether that receive operation has been completed. The send side doesn't have to wait for the receive side to call MPI_WAIT in order for the send to complete.

I'm not sure there's any semantic difference between "... the receive should complete..." versus "... the receive must complete...", but the latter does seem stronger.

-Ron

On Nov 26, 2012, at 11:44 AM, Bronis R. de Supinski wrote:

> 
> Scott:
> 
> The problem with your suggestion is that completion
> has a well defined meaning in MPI that requires the
> completion call. If the receive completed without
> any call then a subsequent attempt to complete it
> would be an error. I believe that is reason the term
> "satisfied" was used.
> 
> Bronis
> 
> 
> 
> On Mon, 26 Nov 2012, Pavan Balaji wrote:
> 
>> Scott,
>> 
>> I'm not sure.  I've cc'ed the list on this email.
>> 
>> -- Pavan
>> 
>> On 11/26/2012 10:42 AM US Central Time, Scott Pakin wrote:
>>> Pavan,
>>> 
>>> On 11/19/2012 11:59 PM, Pavan Balaji wrote:
>>>>> Thanks.  I didn't see the email come through, though.
>>> Do you know if email from non-subscribers gets silently dropped?
>>> 
>>> I attached the message I tried posting.  Want to try resending it
>>> yourself?  If not, I suppose I can subscribe, resend, then probably
>>> unsubscribe.
>>> 
>>> Thanks,
>>> -- Scott
>>> 
>>> 
>>> Attached Message
>>> 
>>> Subject:
>>> Unclear wording in MPI spec
>>> From:
>>> Scott Pakin <pakin at lanl.gov>
>>> Date:
>>> 11/19/2012 11:14 AM
>>> 
>>> To:
>>> <mpi-forum at lists.mpi-forum.org>
>>> 
>>> 
>>> From a discussion I had with Pavan Balaji at SC'12, I believe a minor
>>> wording change is needed in the MPI 3.0 standard, page 56, lines
>>> 30-35:
>>> 
>>>    Progress: A call to MPI_WAIT that completes a receive will
>>>    eventually terminate and return if a matching send has been
>>>    started, unless the send is satisfied by another receive. In
>>>    particular, if the matching send is nonblocking, then the receive
>>>    should complete even if no call is executed by the sender to
>>>    complete the send.  Similarly, a call to MPI_WAIT that completes a
>>>    send will eventually return if a matching receive has been
>>>    started, unless the receive is satisfied by another send, and even
>>>    if no call is executed to complete the receive.
>>> 
>>> Perhaps that should say, "...the receive *is required* to complete
>>> even if no call is executed...".
>>> 
>>> -- Scott
>> 
>> -- 
>> Pavan Balaji
>> http://www.mcs.anl.gov/~balaji
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>> 
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