Actual source code: ex2.c

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

      4: /*T
      5:    Concepts: petsc^introduction
      6:    Concepts: printing^synchronized
      7:    Concepts: printing^in parallel
      8:    Concepts: printf^synchronized
      9:    Concepts: printf^in parallel
     10:    Processors: n
     11: T*/

     15: #include <petscsys.h>
     16: int main(int argc,char **argv)
     17: {
     19:   PetscMPIInt    rank,size;

     21:   /*
     22:     Every PETSc program should begin with the PetscInitialize() routine.
     23:     argc, argv - These command line arguments are taken to extract the options
     24:                  supplied to PETSc and options supplied to MPI.
     25:     help       - When PETSc executable is invoked with the option -help,
     26:                  it prints the various options that can be applied at
     27:                  runtime.  The user can use the "help" variable place
     28:                  additional help messages in this printout.
     29:   */
     30:   PetscInitialize(&argc,&argv,NULL,help);if (ierr) return ierr;

     32:   /*
     33:      The following MPI calls return the number of processes
     34:      being used and the rank of this process in the group.
     35:    */
     36:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
     37:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

     39:   /*
     40:      Here we would like to print only one message that represents
     41:      all the processes in the group.  We use PetscPrintf() with the
     42:      communicator PETSC_COMM_WORLD.  Thus, only one message is
     43:      printed representing PETSC_COMM_WORLD, i.e., all the processors.
     44:   */
     45:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);
     46:   /*
     47:      Here we would like to print info from each process, such that
     48:      output from process "n" appears after output from process "n-1".
     49:      To do this we use a combination of PetscSynchronizedPrintf() and
     50:      PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
     51:      All the processes print the message, one after another.
     52:      PetscSynchronizedFlush() indicates that the current process in the
     53:      given communicator has concluded printing, so that the next process
     54:      in the communicator can begin printing to the screen.
     55:      */
     56:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World.\n",rank);
     57:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World - Part II.\n",rank);
     58:   PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);
     59:   /*
     60:     Here a barrier is used to separate the two states.
     61:   */
     62:   MPI_Barrier(PETSC_COMM_WORLD);

     64:   /*
     65:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
     66:     (where each process is considered separately).  Thus, this time the
     67:     output from different processes does not appear in any particular order.
     68:   */
     69:   PetscPrintf(PETSC_COMM_SELF,"[%d] Jumbled Hello World\n",rank);

     71:   /*
     72:      Always call PetscFinalize() before exiting a program.  This routine
     73:        - finalizes the PETSc libraries as well as MPI
     74:        - provides summary and diagnostic information if certain runtime
     75:          options are chosen (e.g., -log_view).
     76:      See the PetscFinalize() manpage for more information.
     77:   */
     78:   PetscFinalize();
     79:   return ierr;
     80: }

     83: /*TEST

     85:    test:

     87: TEST*/