Actual source code: ex2.c


  2: static char help[] = "Synchronized printing.\n\n";

  4: #include <petscsys.h>
  5: int main(int argc, char **argv)
  6: {
  7:   PetscMPIInt rank, size;

  9:   /*
 10:     Every PETSc program should begin with the PetscInitialize() routine.
 11:     argc, argv - These command line arguments are taken to extract the options
 12:                  supplied to PETSc and options supplied to MPI.
 13:     help       - When PETSc executable is invoked with the option -help,
 14:                  it prints the various options that can be applied at
 15:                  runtime.  The user can use the "help" variable to place
 16:                  additional help messages in this printout.
 17:   */
 19:   PetscInitialize(&argc, &argv, NULL, help);

 21:   /*
 22:      The following MPI calls return the number of processes
 23:      being used and the rank of this process in the group.
 24:    */
 25:   MPI_Comm_size(PETSC_COMM_WORLD, &size);
 26:   MPI_Comm_rank(PETSC_COMM_WORLD, &rank);

 28:   /*
 29:      Here we would like to print only one message that represents
 30:      all the processes in the group.  We use PetscPrintf() with the
 31:      communicator PETSC_COMM_WORLD.  Thus, only one message is
 32:      printed representing PETSC_COMM_WORLD, i.e., all the processors.
 33:   */
 34:   PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank);
 35:   /*
 36:      Here we would like to print info from each process, such that
 37:      output from process "n" appears after output from process "n-1".
 38:      To do this we use a combination of PetscSynchronizedPrintf() and
 39:      PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
 40:      All the processes print the message, one after another.
 41:      PetscSynchronizedFlush() indicates that the current process in the
 42:      given communicator has concluded printing, so that the next process
 43:      in the communicator can begin printing to the screen.
 44:      */
 45:   PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] Synchronized Hello World.\n", rank);
 46:   PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] Synchronized Hello World - Part II.\n", rank);
 47:   PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT);
 48:   /*
 49:     Here a barrier is used to separate the two states.
 50:   */
 51:   MPI_Barrier(PETSC_COMM_WORLD);

 53:   /*
 54:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
 55:     (where each process is considered separately).  Thus, this time the
 56:     output from different processes does not appear in any particular order.
 57:   */
 58:   PetscPrintf(PETSC_COMM_SELF, "[%d] Jumbled Hello World\n", rank);

 60:   /*
 61:      Always call PetscFinalize() before exiting a program.  This routine
 62:        - finalizes the PETSc libraries as well as MPI
 63:        - provides summary and diagnostic information if certain runtime
 64:          options are chosen (e.g., -log_view).
 65:      See the PetscFinalize() manpage for more information.
 66:   */
 67:   PetscFinalize();
 68:   return 0;
 69: }

 71: /*TEST

 73:    test:

 75: TEST*/