xbt_dict_foreach(smpi_instances, cursor, name, instance) {
if(instance->comm_world!=MPI_COMM_NULL)
while (instance->comm_world->group()->unuse() > 0);
xbt_dict_foreach(smpi_instances, cursor, name, instance) {
if(instance->comm_world!=MPI_COMM_NULL)
while (instance->comm_world->group()->unuse() > 0);