Actual source code: ex2.c

      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*/