Actual source code: ex2.c
2: static char help = "Synchronized printing.\n\n";
4: #include <petscsys.h>
5: int main(int argc, char **argv)
7: PetscMPIInt rank, size;
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.
19: PetscInitialize(&argc, &argv, NULL, help);
22: The following MPI calls return the number of processes
23: being used and the rank of this process in the group.
25: MPI_Comm_size(PETSC_COMM_WORLD, &size);
26: MPI_Comm_rank(PETSC_COMM_WORLD, &rank);
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.
34: PetscPrintf(PETSC_COMM_WORLD, "Number of processors = %d, rank = %d\n", size, rank);
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.
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);
49: Here a barrier is used to separate the two states.
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.
58: PetscPrintf(PETSC_COMM_SELF, "[%d] Jumbled Hello World\n", rank);
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.
68: return 0;