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Subject: Re: [OMPI users] multi-threaded programming
From: Durga Choudhury (dpchoudh_at_[hidden])
Date: 2011-03-08 14:10:20


A follow-up question (and pardon if this sounds stupid) is this:

If I want to make my process multithreaded, BUT only one thread has
anything to do with MPI (for example, using OpenMP inside MPI), then
the results will be correct EVEN IF #1 or #2 of Eugene holds true. Is
this correct?

Thanks
Durga

On Tue, Mar 8, 2011 at 12:34 PM, Eugene Loh <eugene.loh_at_[hidden]> wrote:
> Let's say you have multi-threaded MPI processes, you request
> MPI_THREAD_MULTIPLE and get MPI_THREAD_MULTIPLE, and you use the self,sm,tcp
> BTLs (which have some degree of threading support).  Is it okay to have an
> [MPI_Isend|MPI_Irecv] on one thread be completed by an MPI_Wait on another
> thread?  I'm assuming some sort of synchronization and memory barrier/flush
> in between to protect against funny race conditions.
>
> If it makes things any easier on you, we can do this multiple-choice style:
>
> 1)  Forbidden by the MPI standard.
> 2)  Not forbidden by the MPI standard, but will not work with OMPI (not even
> with the BTLs that claim to be multi-threaded).
> 3)  Works well with OMPI (provided you use a BTL that's multi-threaded).
>
> It's looking like #2 to me, but I'm not sure.
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