Wesley, I haven't read the test case code, but based on the description in this thread I think this is probably a duplicate of ticket #1502: http://trac.mpich.org/projects/mpich/ticket/1502 FWIW, I think that issue has since been fixed in Open MPI, though I haven't tested it myself. -Dave On Sep 26, 2014, at 11:29 AM, Wesley Bland <[email protected]> wrote:

I believe that your code is correct. I’ve gone through it to simplify things a bit (attached) and see the same errors as you. That’s probably a bug in MPICH that needs to be fixed unless someone else comes along and says that for MPI_INTERCOMM_CREATE to work, all processes must be in the same peer_comm, which doesn’t seem to be what the standard says to me. I’ll create a ticket and add you as a CC so you can keep track of things.

In the meantime, you can avoid this problem by using one of the other ways of setting up communication between two group of processes. You can use the connect/accept functions as per this ticket: http://trac.mpich.org/projects/mpich/ticket/495 or you can change the way you spawn processes to have all processes in MPI_COMM_WORLD be involved in spawning the new processes. I don’t know if that will actually work for your application, but it’s a stopgap measure while we fix this bug.

Thanks, Wesley

...

On Sep 26, 2014, at 10:50 AM, Carsten Clauss <[email protected]> wrote:

Dear all,

I have a code where two processes (forming the original MPI_COMM_WORLD) each spawn one additional child process (using MPI_COMM_SELF as spawning group).

Now I want to create an intra-comm that covers all of these four processes.

For doing so, I initially merge the two inter-comms resulting from the spawn calls into two new intra-comms (by using MPI_Intercomm_merge()).

Then I create via MPI_intercomm_create() a new inter-comm that connects these two by using the original world communicator as peer-com.

Finally, I merge the resulting inter-comm into the desired intra-comm.

When using Open MPI, my code (it's derived from the MPICH test spaiccreate2.c, see attachment) works fine on my local machine. However, when running it with MPICH-3.1.2, I get the following error message:

PMPI_Intercomm_create(601).....: MPI_Intercomm_create(comm=0x84000006, local_leader=1, MPI_COMM_WORLD, remote_leader=1, tag=123, newintercomm=0x7fff8323ee3c) failed MPIR_Intercomm_create_impl(258): MPID_GPID_ToLpidArray(461).....: Internal MPI error: Unknown gpid (1809769587)0 Fatal error in PMPI_Intercomm_create: Internal MPI error!, error stack: PMPI_Intercomm_create(601).....: MPI_Intercomm_create(comm=0x84000004, local_leader=1, MPI_COMM_WORLD, remote_leader=0, tag=123, newintercomm=0x7fff6e0b4c7c) failed MPIR_Intercomm_create_impl(258): MPID_GPID_ToLpidArray(461).....: Internal MPI error: Unknown gpid (1607388239)0

Here are my questions: 1) Is the above mentioned approach the right way to reach my goal? 2) Is the semantics of the attached code MPI compliant? 3) What is the reason for the error message when using MPICH?

Thanks in advance and with kind regards, Carsten

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