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*/
13: #include <petscsys.h>
14: int main(int argc,char **argv)
15: {
16: PetscMPIInt rank,size;
18: /*
19: Every PETSc program should begin with the PetscInitialize() routine.
20: argc, argv - These command line arguments are taken to extract the options
21: supplied to PETSc and options supplied to MPI.
22: help - When PETSc executable is invoked with the option -help,
23: it prints the various options that can be applied at
24: runtime. The user can use the "help" variable to place
25: additional help messages in this printout.
26: */
27: PetscInitialize(&argc,&argv,NULL,help);
29: /*
30: The following MPI calls return the number of processes
31: being used and the rank of this process in the group.
32: */
33: MPI_Comm_size(PETSC_COMM_WORLD,&size);
34: MPI_Comm_rank(PETSC_COMM_WORLD,&rank);
36: /*
37: Here we would like to print only one message that represents
38: all the processes in the group. We use PetscPrintf() with the
39: communicator PETSC_COMM_WORLD. Thus, only one message is
40: printed representing PETSC_COMM_WORLD, i.e., all the processors.
41: */
42: PetscPrintf(PETSC_COMM_WORLD,"Number of processors = %d, rank = %d\n",size,rank);
43: /*
44: Here we would like to print info from each process, such that
45: output from process "n" appears after output from process "n-1".
46: To do this we use a combination of PetscSynchronizedPrintf() and
47: PetscSynchronizedFlush() with the communicator PETSC_COMM_WORLD.
48: All the processes print the message, one after another.
49: PetscSynchronizedFlush() indicates that the current process in the
50: given communicator has concluded printing, so that the next process
51: in the communicator can begin printing to the screen.
52: */
53: PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World.\n",rank);
54: PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World - Part II.\n",rank);
55: PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT);
56: /*
57: Here a barrier is used to separate the two states.
58: */
59: MPI_Barrier(PETSC_COMM_WORLD);
61: /*
62: Here we simply use PetscPrintf() with the communicator PETSC_COMM_SELF
63: (where each process is considered separately). Thus, this time the
64: output from different processes does not appear in any particular order.
65: */
66: PetscPrintf(PETSC_COMM_SELF,"[%d] Jumbled Hello World\n",rank);
68: /*
69: Always call PetscFinalize() before exiting a program. This routine
70: - finalizes the PETSc libraries as well as MPI
71: - provides summary and diagnostic information if certain runtime
72: options are chosen (e.g., -log_view).
73: See the PetscFinalize() manpage for more information.
74: */
75: PetscFinalize();
76: return 0;
77: }
79: /*TEST
81: test:
83: TEST*/