/* manager */ #include "mpi.h" int main(int argc, char *argv[]) { int world_size, universe_size, *universe_sizep, flag; MPI_Comm everyone; /* intercommunicator */ char worker_program[100];MPI_Init(&argc, &argv); MPI_Comm_size(MPI_COMM_WORLD, &world_size);
if (world_size != 1) error("Top heavy with management");
MPI_Attr_get(MPI_COMM_WORLD, MPI_UNIVERSE_SIZE, &universe_sizep, &flag); if (!flag) { printf("This MPI does not support UNIVERSE_SIZE. How many\n\ processes total?"); scanf("%d", &universe_size); } else universe_size = *universe_sizep; if (universe_size == 1) error("No room to start workers");
/* * Now spawn the workers. Note that there is a run-time determination * of what type of worker to spawn, and presumably this calculation must * be done at run time and cannot be calculated before starting * the program. If everything is known when the application is * first started, it is generally better to start them all at once * in a single MPI_COMM_WORLD. */
choose_worker_program(worker_program); MPI_Comm_spawn(worker_program, MPI_ARGV_NULL, universe_size-1, MPI_INFO_NULL, 0, MPI_COMM_SELF, &everyone, MPI_ERRCODES_IGNORE); /* * Parallel code here. The communicator "everyone" can be used * to communicate with the spawned processes, which have ranks 0,.. * MPI_UNIVERSE_SIZE-1 in the remote group of the intercommunicator * "everyone". */
MPI_Finalize(); return 0; }
/* worker */#include "mpi.h" int main(int argc, char *argv[]) { int size; MPI_Comm parent; MPI_Init(&argc, &argv); MPI_Comm_get_parent(&parent); if (parent == MPI_COMM_NULL) error("No parent!"); MPI_Comm_remote_size(parent, &size); if (size != 1) error("Something's wrong with the parent");
/* * Parallel code here. * The manager is represented as the process with rank 0 in (the remote * group of) MPI_COMM_PARENT. If the workers need to communicate among * themselves, they can use MPI_COMM_WORLD. */
MPI_Finalize(); return 0; }