I recommend that you read "Semantics of Point-to-Point Communication" in the MPI standard (section 3.5 in MPI 3.1).  It has all of the information that you seek.

Best,

Jeff


On Tue, Oct 20, 2015 at 7:58 AM, Dorier, Matthieu <mdorier@anl.gov> wrote:
>
> Hi,
>
> In my program I have a loop of this form:
>
> loop {
>   MPI_Send(small message)
>   MPI_Isend(big message)
> }
> do_some_computation()
> MPI_Waitall
>
> The sends and isends all have the same target rank.
>
> Is there a risk that an MPI_Send forces a previously posted MPI_Isend to complete before it can complete itself (in which case I would loose the benefit of using non-blocking sends)?
>
> Thanks,
>
> Matthieu
>
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--
Jeff Hammond
jeff.science@gmail.com
http://jeffhammond.github.io/