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

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

  8:   /*
  9:     Every PETSc program should begin with the PetscInitialize() routine.
 10:     argc, argv - These command line arguments are taken to extract the options
 11:                  supplied to PETSc and options supplied to MPI.
 12:     help       - When PETSc executable is invoked with the option -help,
 13:                  it prints the various options that can be applied at
 14:                  runtime.  The user can use the "help" variable to place
 15:                  additional help messages in this printout.
 16:   */
 17:   PetscFunctionBeginUser;
 18:   PetscCall(PetscInitialize(&argc, &argv, NULL, help));

 20:   /*
 21:      The following MPI calls return the number of processes
 22:      being used and the rank of this process in the group.
 23:    */
 24:   PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD, &size));
 25:   PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD, &rank));

 27:   /*
 28:      Here we would like to print only one message that represents
 29:      all the processes in the group.  We use PetscPrintf() with the
 30:      communicator PETSC_COMM_WORLD.  Thus, only one message is
 31:      printed representing PETSC_COMM_WORLD, i.e., all the processors.
 32:   */
 33:   PetscCall(PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank));
 34:   /*
 35:      Here we would like to print info from each process, such that
 36:      output from process "n" appears after output from process "n-1".
 37:      To do this we use a combination of PetscSynchronizedPrintf() and
 38:      PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
 39:      All the processes print the message, one after another.
 40:      PetscSynchronizedFlush() indicates that the current process in the
 41:      given communicator has concluded printing, so that the next process
 42:      in the communicator can begin printing to the screen.
 43:      */
 44:   PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] Synchronized Hello World.\n", rank));
 45:   PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD, "[%d] Synchronized Hello World - Part II.\n", rank));
 46:   PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD, PETSC_STDOUT));
 47:   /*
 48:     Here a barrier is used to separate the two states.
 49:   */
 50:   PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD));

 52:   /*
 53:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
 54:     (where each process is considered separately).  Thus, this time the
 55:     output from different processes does not appear in any particular order.
 56:   */
 57:   PetscCall(PetscPrintf(PETSC_COMM_SELF, "[%d] Jumbled Hello World\n", rank));

 59:   /*
 60:      Always call PetscFinalize() before exiting a program.  This routine
 61:        - finalizes the PETSc libraries as well as MPI
 62:        - provides summary and diagnostic information if certain runtime
 63:          options are chosen (e.g., -log_view).
 64:      See the PetscFinalize() manpage for more information.
 65:   */
 66:   PetscCall(PetscFinalize());
 67:   return 0;
 68: }

 70: /*TEST

 72:    test:

 74: TEST*/