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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">A communication that does nothing is not the same as the initialization value of the type. It makes a non-unique mapping of operations to handles too, for no good reason.
<br>
<br>
Imagine that I start my array with MPI_REQUEST_NULL as the default value. Now I can have some of those in the middle of my array even though this is an actual (albeit empty) communication. I have to distinguish now between MPI_REQUEST_NULL being generated
because the work was trivial, vs. because of an uninitialized array element.<br>
<br>
What if I want to test this request too? Does it return completed? :-)<br>
<br>
I think there is a subtle semantic difference between "a no work operation" and MPI_REQUEST_NULL. We need to look at all the possible dark corners of what can happen by the literal mapping.<br>
<br>
I will go re-read 5.2.3 next.<br>
<br>
Its just my opinion, it may be that we decide I am overly worried about a small edge condition.<br>
<br>
Tony<br>
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<p class="p1" style="font-family:Tahoma; font-size:13px"><font size="2">Anthony Skjellum, PhD<br>
</font><span style="font-size:small">Professor of Computer Science and Software Engineering<br>
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</span><font size="2">Samuel Ginn College of Engineering<br>
</font><span style="font-size:13px">Auburn University<br>
</span><span style="font-size:13px">skjellum@auburn.edu or skjellum@gmail.com<br>
</span><span style="font-size:13px">cell: +1-205-807-4968 ; office: +1-334-844-6360</span></p>
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<div style="direction: ltr;" id="divRpF185939"><font face="Tahoma" color="#000000" size="2"><b>From:</b> mpi-forum [mpi-forum-bounces@lists.mpi-forum.org] on behalf of George Bosilca [bosilca@icl.utk.edu]<br>
<b>Sent:</b> Thursday, December 11, 2014 4:50 PM<br>
<b>To:</b> Main MPI Forum mailing list<br>
<b>Subject:</b> Re: [Mpi-forum] behavior of NBC for intracommunicators when root == MPI_PROC_NULL<br>
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<div>What's wrong with 5.2.3? From a practical point of view, returning MPI_REQUEST_NULL makes sense (following the description about communication with MPI_PROC_NULL from 3.11).</div>
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<div> George.<br>
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<div class="gmail_quote">On Thu, Dec 11, 2014 at 5:22 PM, Anthony Skjellum <span dir="ltr">
<<a href="mailto:skjellum@auburn.edu" target="_blank">skjellum@auburn.edu</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex; border-left:1px #ccc solid; padding-left:1ex">
Shouldn't it just be a trivial request -- why map to null ? - shortcut should of course happen internally but the request should be valid --- undesirable side effects possible Imho with a literal mapping !<br>
<br>
Anthony Skjellum, PhD<br>
<a href="tel:205-807-4968" value="+12058074968" target="_blank">205-807-4968</a><br>
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<div class="h5"><br>
<br>
> On Dec 11, 2014, at 3:30 PM, Jeff Hammond <<a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a>> wrote:<br>
><br>
> I would hope that the Ianything is matched with a corresponding<br>
> Test/Wait* call on every process that calls it. To allow otherwise<br>
> seems pretty odd.<br>
><br>
> Presumably, if Ibcast is a no-op when root=MPI_PROC_NULL, then the<br>
> request can be set to MPI_REQUEST_NULL and thus completing it is<br>
> trivial.<br>
><br>
> If the standard says that completing a request known to be<br>
> MPI_REQUEST_NULL is not required, then I suppose the user can avoid<br>
> making the completion call, but I don't like that style.<br>
><br>
> Jeff<br>
><br>
>> On Thu, Dec 11, 2014 at 11:30 AM, Fab Tillier <<a href="mailto:ftillier@microsoft.com" target="_blank">ftillier@microsoft.com</a>> wrote:<br>
>> Hi Folks,<br>
>><br>
>><br>
>><br>
>> I can’t find anything in the standard document that explains the behavior<br>
>> for NBC requests on intercommunicators when root == MPI_PROC_NULL. Taking<br>
>> MPI_Ibcast as an example, what is the output value of request? Is it<br>
>> MPI_REQUEST_NULL? Is it not set at all? Is it a valid request that must be<br>
>> completed?<br>
>><br>
>><br>
>><br>
>> Thanks,<br>
>><br>
>> -Fab<br>
>><br>
>><br>
>> _______________________________________________<br>
>> mpi-forum mailing list<br>
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http://lists.mpi-forum.org/mailman/listinfo.cgi/mpi-forum</a><br>
><br>
><br>
><br>
> --<br>
> Jeff Hammond<br>
> <a href="mailto:jeff.science@gmail.com" target="_blank">jeff.science@gmail.com</a><br>
> <a href="http://jeffhammond.github.io/" target="_blank">http://jeffhammond.github.io/</a><br>
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