In MPICH 3.2, MPI_Ibarrier(MPI_COMM_SELF,&r) returns r == MPI_REQUEST_NULL. This is also the case for other communicators of size 1. Previous versions of MPICH and also all versions of Open MPI return a valid request not equal to MPI_REQUEST_NULL. This bit me because it was natural to compare to MPI_REQUEST_NULL in a conditional for an Ibarrier/Issend/Iprobe algorithm. It can be worked around with a slightly more complicate conditional, but is this change intentional? The call returns a request handle, which must be passed to a completion call. -- MPI-3 §5.12 This does not say "unless the communicator has size 1". _______________________________________________ discuss mailing list [email protected] To manage subscription options or unsubscribe: https://lists.mpich.org/mailman/listinfo/discuss