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Subject: Re: [OMPI users] random MPI_UNIVERSE_SIZE and inter-commicator created by MPI_Comm_spawn
From: George Bosilca (bosilca_at_[hidden])
Date: 2010-02-18 13:46:05


Mathieu,

Your MPI_COMM_UNIVERSE is a inter-communicator, and therefore the MPI_Comm_size and MPI_Comm_rank return the size, respectively the rank, in the local group. There is a special accessor for getting the remote group size (MPI_Comm_remote_size).

Now regarding the previous question (about the attribute MPI_UNIVERSE_SIZE), your answer is in the MPI standard 2.2 page 346 line 35. The MPI_UNIVERSE_SIZE is not set in Open MPI.

  george.

On Feb 18, 2010, at 10:18 , Mathieu Gontier wrote:

>
> Another question on the same example.
>
> When I ask the size on the inter-communitator (MPI_COMM_UNIVERSE in the example) between the spaner/parent and the spawned/children processes, the same number of processes than in MPI_COMM_WORLD is returned. I do not really understand because I expected my MPI_COMM_UNIVERSE be a higher communicator including here the group of MPI_COMM_SELF and the group of MPI_COMM_WORLD of my spawned application (./worker).
> I think I missed something. Does someone can help me?
>
> Thank you.
>
> Mathieu Gontier wrote:
>>
>>
>> Hello,
>>
>> I am trying to use MPI_Comm_spawn (MPI-2 standard only) and I have an problem when I use MPI_UNIVERSE_SIZE. Here my code:
>>
>> int main( int argc, char *argv[] )
>> {
>> int wsize=0, wrank=-1 ;
>> int usize=0, urank=-1 ;
>> int ier ;
>> int usize_attr=0, flag=0 ;
>> MPI_Comm MPI_COMM_UNIVERSE;
>> ier = MPI_Init( &argc, &argv ) ;
>> ier = MPI_Comm_size( MPI_COMM_WORLD, &wsize ) ;
>> ier = MPI_Comm_rank( MPI_COMM_WORLD, &wrank ) ;
>> ier = MPI_Comm_get_attr( MPI_COMM_WORLD, MPI_UNIVERSE_SIZE, (void*) &usize_attr, &flag ) ;
>> if ( !flag ) { printf( "[manager][error] This MPI does not support MPI_UNIVERSE_SIZE.\n" ) ; return 1 ; }
>> if( wrank==0 ) {
>> ier = MPI_Comm_spawn( "./worker", argv, ( wsize/2 > 2 ? wsize/2 : 2 ), MPI_INFO_NULL, 0, MPI_COMM_SELF, &MPI_COMM_UNIVERSE, MPI_ERRCODES_IGNORE);
>> ier = MPI_Comm_size( MPI_COMM_UNIVERSE, &usize ) ;
>> ier = MPI_Comm_rank( MPI_COMM_UNIVERSE, &urank ) ;
>> }
>> printf( "[manager] I am the process %d on %d in world (universe attr size: %d) and %d on %d in universe\n", wrank, wsize, usize_attr, urank, usize ) ;
>> MPI_Finalize();
>> return 0;
>> }
>>
>> When I call MPI_Comm_get_attr() with MPI_UNIVERSE_SIZE, my variable u_size_attr is random. Any idea?
>>
>> Thank you.
>>
>>
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>
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