[mpich-discuss] Order of completion in MPI_Waitany

Thomas Ropars thomas.ropars at epfl.ch
Fri Sep 20 02:57:27 CDT 2013

Hi Matthieu,

MPI does not provide any guarantee on the completion order of the 
reception requests in this case. More generally, regarding waitAny, the 
MPI-3.0 specification says that "If more than one operation is enabled 
and can terminate, one is arbitrarily


On 09/19/2013 04:31 PM, Matthieu Dorier wrote:
> Hi,
> I would like a precision on the semantics of MPI_Waitany in this 
> situation:
> - Process 1 does 2 MPI_Irecv with different tags A and B (the order 
> doesn't matter); it then waits on the two requests with MPI_Waitany.
> - In the mean time, process 2 does an MPI_Send with tag A, then 
> MPI_Send with tag B.
> Can I ensure that MPI_Waitany will always give me the index of the 
> message corresponding to the first MPI_Send, i.e. the one with the tag 
> A, even in situations where process 1 called MPI_Irecv on a tag B first?
> Thanks
> Matthieu Dorier
> PhD student at ENS Cachan Brittany and IRISA
> http://people.irisa.fr/Matthieu.Dorier
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