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
chosen".

Thomas

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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