[mpich-discuss] Issues with MPI_Comm_create

[Arthur Wu]

Hi There,

I am trying to create a new communicator using the
following textbook code. However, the created
communicator is always MPI_COMM_NULL, as shown in the
runtime error message. Since I could not find any
example code in MPICH2 regarding communicator
creation, my questions is this: does MPICH2 currently
support creation of new communicators?

Thanks a lot.

Arthur Wu

>  
> // create the worker communicator
>     MPI_Group world_group, work_group;
>     MPI_Comm  work_comm;
>     int       excl_ranks[2];
>     int nn=0;
>  
>     excl_ranks[0] = 1;
>     excl_ranks[1] = 2;
>     MPI_Comm_group(MPI_COMM_WORLD, &world_group);
>     MPI_Group_incl(world_group, 2, excl_ranks,
> &work_group);
>     MPI_Comm_create(MPI_COMM_WORLD, work_group,
> &work_comm);
>     MPI_Comm_size(work_comm, &nn);
>  
>     fprintf(stderr,  "Sub comm size = %i\n", nn );
>  

Runtime errors:

> 
> C:\public\bin>mpiexec -n 3 -machinefile Config.txt
> c:\public\bin\MpiApp.exe c:\t
> emp\mpi\7 input.txt output.txt log.txt
> Process   1 of 3 on
> B00123F4418EA.corp.bankofamerica.com (pid 2168)
> Process   0 of 3 on
> B00123F4418EA.corp.bankofamerica.com (pid 4440)
> Process   2 of 3 on
> B000BCD9949B9.corp.bankofamerica.com (pid 208)
>  
> job aborted:
> rank: node: exit code[: error message]
> 0: B00123F4418EA: 1: Fatal error in MPI_Comm_size:
> Invalid communicator,
> error s
> tack:
> MPI_Comm_size(112): MPI_Comm_size(MPI_COMM_NULL,
> size=000FED08) failed
> MPI_Comm_size(70).: Null communicator
> 1: B00123F4418EA: 1
> 2: b000bcd9949b9: 1
>  
>  


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