On Jun 15, 2012, at 4:38 PM, Ramesh Vinayagam wrote:
> I was looking more into this scenario :
>
> if (rank ==0){
> MPI_Send(&tmp,2048, MPI_INT, 1,123, myComm);
> MPI_Recv(&tmp2,2048, MPI_INT, 1,321,
> MPI_COMM_WORLD, MPI_STATUS_IGNORE);
> }
> if (rank == 1){
> MPI_Send(&tmp1,2048, MPI_INT, 0,321, MPI_COMM_WORLD);
> MPI_Recv(&tmp3,2048, MPI_INT, 0,123, myComm, MPI_STATUS_IGNORE);
>
> }
>
> This scenario in a normal case will lead to a deadlock. But I was wondering
> whether multiple communicators will solve this issue, but apparently it
> doesn't.
No, it does not.
You can use non-blocking communications, instead.
> I tried doing sends and receives on different threads, but that did not help
> too. So I was wondering if there is a way to handle this in MPI without
> using non-blocking sends and receives.
You could use MPI_Sendrecv().
> Thanks
> Ramesh
>
>
> On Fri, Jun 15, 2012 at 3:40 AM, Jeff Squyres <jsquy...@cisco.com> wrote:
> On Jun 14, 2012, at 8:43 PM, Ramesh Vinayagam wrote:
>
> > I was wondering is there a way to communicate between two processes with
> > two different communicators simultaneously in MPI? Like having two channels
> > for communication?
>
> I'm not quite sure what you're asking. Are you asking if it's possible to
> have 2 processes share 2 entirely different communicators (and use both of
> them for communication)?
>
> If so, yes. Any set of processes can have any number of shared
> communicators. For example:
>
> MPI_Comm foo;
> MPI_Comm_dup(MPI_COMM_WORLD, &foo);
>
> Now foo will be a duplicate of MPI_COMM_WORLD, but with a different
> communication context (so that messages sent on MCW won't be received on foo,
> and vice versa). Hence, you can send a message on MCW to any peer in that
> communicator, but you can also send a message on foo to any peer in that
> communicator.
>
> Note, however, that sending multiple messages on different communicators to
> the same peer doesn't (usually) expand your available bandwidth. Think of
> communicators (and tags, too), as message matching mechanisms rather than
> bandwidth-multiplying mechanisms. For example, you might send control
> messages on "foo", but send data messages on MPI_COMM_WORLD.
>
> Hope that helps.
>
> --
> Jeff Squyres
> jsquy...@cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
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--
Jeff Squyres
jsquy...@cisco.com
For corporate legal information go to:
http://www.cisco.com/web/about/doing_business/legal/cri/
