[mpich2-dev] Weird behavior collective routine

[Simone Atzeni]

Hi,

According to the MPI-2 Standard about collectives routine at page 132  
(Section 5.2.1), it says "All processes in the group
identified by the intracommunicator must call the collective routine  
with matching arguments".

Running the program below using MPICH:

if (rank == 0) {

} else if (rank == 1) {
     MPI_Reduce(&u, &v, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
} else if (rank == 2) {
     MPI_Reduce(&u, &v, 1, MPI_INT, MPI_SUM, 0, MPI_COMM_WORLD);
}

it terminates correctly, but it shouldn't be in agreement whit the  
standard because all process in the group (MPI_COMM_WORLD in this  
case) must call the collective routine. In this case  the root process  
does not call the REDUCE routine, so where do all the messages from  
other MPI_Reduce end up?

Another program, using Broadcast routine:

if (rank == 0) {
     MPI_Bcast(&u, 1, MPI_INT, 0, MPI_COMM_WORLD);
}
else if (rank == 1) {

}  else if (rank == 2) {
     MPI_Bcast(&v, 1, MPI_INT, 0, MPI_COMM_WORLD);
}

it also terminates correctly, but also in this case not all process in  
the group (MPI_COMM_WORLD) call the collective routine. So it seems  
that also in this case the standard is not enforced. So where does the  
message to process 1 end up?


I tried the same programs with Open MPI and they have the same  
behavior, but using Microsoft MPI both programs crash.
So, the question is, MPICH2 and Open MPI don't enforce the standard  
and only Microsoft MPI enforces it?

Thanks
Regards
Simone
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