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*/

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

 19:   /*
 20:     Every PETSc program should begin with the PetscInitialize() routine.
 21:     argc, argv - These command line arguments are taken to extract the options
 22:                  supplied to PETSc and options supplied to MPI.
 23:     help       - When PETSc executable is invoked with the option -help,
 24:                  it prints the various options that can be applied at
 25:                  runtime.  The user can use the "help" variable place
 26:                  additional help messages in this printout.
 27:   */
 28:   PetscInitialize(&argc,&argv,NULL,help);

 30:   /*
 31:      The following MPI calls return the number of processes
 32:      being used and the rank of this process in the group.
 33:    */
 34:   MPI_Comm_size(PETSC_COMM_WORLD,&size);
 35:   MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

 37:   /*
 38:      Here we would like to print only one message that represents
 39:      all the processes in the group.  We use PetscPrintf() with the
 40:      communicator PETSC_COMM_WORLD.  Thus, only one message is
 41:      printed representing PETSC_COMM_WORLD, i.e., all the processors.
 42:   */
 43:   PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);
 44:   /*
 45:      Here we would like to print info from each process, such that
 46:      output from process "n" appears after output from process "n-1".
 47:      To do this we use a combination of PetscSynchronizedPrintf() and
 48:      PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
 49:      All the processes print the message, one after another.
 50:      PetscSynchronizedFlush() indicates that the current process in the
 51:      given communicator has concluded printing, so that the next process
 52:      in the communicator can begin printing to the screen.
 53:      */
 54:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World.\n",rank);
 55:   PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World - Part II.\n",rank);
 56:   PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);
 57:   /*
 58:     Here a barrier is used to separate the two states.
 59:   */
 60:   MPI_Barrier(PETSC_COMM_WORLD);

 62:   /*
 63:     Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
 64:     (where each process is considered separately).  Thus, this time the
 65:     output from different processes does not appear in any particular order.
 66:   */
 67:   PetscPrintf(PETSC_COMM_SELF,"[%d] Jumbled Hello World\n",rank);

 69:   /*
 70:      Always call PetscFinalize() before exiting a program.  This routine
 71:        - finalizes the PETSc libraries as well as MPI
 72:        - provides summary and diagnostic information if certain runtime
 73:          options are chosen (e.g., -log_summary).
 74:      See the PetscFinalize() manpage for more information.
 75:   */
 76:   PetscFinalize();
 77:   return 0;
 78: }