[mpich-discuss] Order of completion in MPI_Waitany

[Matthieu Dorier]

Thanks Thomas! 

----- Mail original -----

> De: "Thomas Ropars" <thomas.ropars at epfl.ch>
> À: discuss at mpich.org
> Envoyé: Vendredi 20 Septembre 2013 09:57:27
> Objet: Re: [mpich-discuss] Order of completion in MPI_Waitany

> 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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