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Subject: Re: [OMPI users] MPI_Comm_dup hangs
From: Prentice Bisbal (prentice_at_[hidden])
Date: 2010-02-04 00:35:03


Nevermind... I figured this one out on my own. I was calling foo() from
inside an if (rank == 0) block. Since MPI_Comm_dup is a collective
operation, it was waiting for all the other nodes to also call
MPI_Comm_dup. Oops.

--
Prentice
Prentice Bisbal wrote:
> I have a problem with MPI_Comm_dup. When I call it in a function, it
> causes my application to hang. Are they any common causes for a problem
> like this? I'm using OpenMPI 1.2.8. Are there any known bugs that could
> be causing this?
> 
> My program seems to hang when it gets to MPI_Comm_dup. Here's an example
> of how I'm using it.
> 
> #include "foo.h"
> 
> /* MPI variables */
> int my_rank;
> int num_proc;
> MPI_Comm euclid_comm;
> 
> void foo(long *arg1, long *arg2, MPI_Comm old_comm);
> 
> int main (int argc, char** argv) {
> 
>   /* get options */
> 
>   MPI_Init(&argc, &argv);
>   MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);
>   MPI_Comm_size(MPI_COMM_WORLD, &num_proc);
> 
>  /* read in some data, yadda, yadda yadda */
> 
>  foo(&arg1, &arg2, MPI_COMM_WORLD);
> 
>  / *print results from foo */
> 
>  MPI_Finalize();
> 
> }
> 
> void foo(long *arg1, long *arg2, MPI_Comm old_comm)
> {
>   MPI_Comm foo_comm;
>   int foo_my_rank;
>   int foo_num_proc;
> 
>   MPI_Comm_dup(old_comm, &foo_comm);
>   MPI_Comm_rank(foo_comm, &foo_my_rank);
>   MPI_Comm_size(foo_comm, &foo_num_proc);
> 
>   /* do stuff */
> 
> }
> 
>