[mpich-discuss] Generalized request classes

[Jim Dinan]

MPI Grequests do generally require external progress, usually polling or a
thread.  It would be nice to see if we can make progress on the MPIX
Grequests proposal.  There are several unresolved issues holding up this
proposal.  Off the top of my head: What progress must MPI provide for the
MPIX Grequest?  How does this affect performance of implementations that do
messaging in hardware?  What can one do from within the polling function
(make MPI calls, allocate memory, etc)?

Your question about Iprobe is interesting...  One could imagine doing an
MPI_Waitany on several communications, including one to receive a message
of unknown length.  I think the only way to do this right now would be to
poll using Iprobe and Testany.

 ~Jim.


On Sun, Aug 4, 2013 at 6:24 PM, Rajeev Thakur <thakur at mcs.anl.gov> wrote:

> MPI_Iprobe does not do any communication itself. It doesn't do a receive,
> for example. So there is no need to call test/wait after an Iprobe, since
> there is nothing to complete. Hence no request object.
>
> Rajev
>
>
> On Aug 4, 2013, at 12:05 PM, Matthieu Dorier wrote:
>
> > Hi,
> >
> > Is there any hope that the currently non-standard generalized request
> interface (MPIX_Grequest_*) in mpich eventually becomes part of the
> standard (or something that looks like this API)?
> > I just spent two days hopelessly trying to develop something with the
> standard generalized requests, but gave up: this API is basically useless
> unless a thread is used to do the MPI_Grequest_complete.
> >
> > For information, what I was trying to do was a custom version of
> MPI_Iprobe that takes an MPI_Request* parameter instead of a int* flag and
> an MPI_Status*, in order to be able to call MPI_{Wait,Test}{all,any,some}
> on requests generated by different types of non-blocking operations
> including MPI_Iprob. (btw, is there a reason why MPI_Iprob doesn't have
> this signature already? That would have make more sense, in my opinion).
> >
> > Matthieu Dorier
> > PhD student at ENS Cachan Brittany and IRISA
> > http://people.irisa.fr/Matthieu.Dorier
> > _______________________________________________
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