[Mpi-forum] MPI "Allocate receive" proposal

[Pavan Balaji]

Where are you providing the buffer information?  Where will the message be received to?

 -- Pavan

On Aug 30, 2013, at 7:27 PM, Matthieu Dorier wrote:

> What I actually meant is rather a version of MPI_Iprobe that uses an MPI_Request argument rather than a (flag, status) pair.
> 
> Matthieu
> 
> ----- Mail original -----
>> De: "Matthieu Dorier" <matthieu.dorier at irisa.fr>
>> À: "Main MPI Forum mailing list" <mpi-forum at lists.mpi-forum.org>
>> Envoyé: Samedi 31 Août 2013 02:23:07
>> Objet: Re: [Mpi-forum] MPI "Allocate receive" proposal
>> 
>> Sorry I only read only half of the exchanges, but I see many open
>> questions here while another solution could be easier and more
>> elegant, in my opinion: just provide MPI_Iprobe.
>> 
>> The main problem we have here is the fact that it is not possible to
>> use MPI_Probe in a Wait/Test array, which I agree is an important
>> problem (I ran into it myself no later than this summer). Yet from
>> the MPI_Arecv proposal, my immediate question is "What if I don't
>> want MPI to use malloc but another function (e.g. cudaMalloc, or any
>> other custom allocators, for instance those from the C++ STL, or an
>> allocator that allocates in a shared memory, etc.)?"
>> 
>> MPI_Iprobe(int source, int tag, MPI_Comm comm, MPI_Request* req)
>> seems to resolve everything: we can use the request in a test/wait
>> array, as soon as it completes we can get the status using
>> MPI_Request_get_status, and get all the informations we would have
>> had from a normal MPI_Probe. From there, the user is free to
>> allocate its buffer the way she wants, and do either an MPI_Recv or
>> an MPI_Irecv with this buffer.
>> 
>> To be honest I also don't like the idea of having a library
>> internally allocate memory for me that I should free outside of the
>> library afterward (except if it's specifically the goal of that
>> library), it's a good way of forgetting to free the buffer and it
>> disallows any flexibility in the way the memory is allocated.
>> 
>> Matthieu
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>> 
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--
Pavan Balaji
http://www.mcs.anl.gov/~balaji