1 2 static char help[] = "Synchronized printing.\n\n"; 3 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*/ 12 13 #include <petscsys.h> 14 int main(int argc,char **argv) 15 { 16 PetscMPIInt rank,size; 17 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 PetscCall(PetscInitialize(&argc,&argv,NULL,help)); 28 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 PetscCallMPI(MPI_Comm_size(PETSC_COMM_WORLD,&size)); 34 PetscCallMPI(MPI_Comm_rank(PETSC_COMM_WORLD,&rank)); 35 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 PetscCall(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 PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World.\n",rank)); 54 PetscCall(PetscSynchronizedPrintf(PETSC_COMM_WORLD,"[%d] Synchronized Hello World - Part II.\n",rank)); 55 PetscCall(PetscSynchronizedFlush(PETSC_COMM_WORLD,PETSC_STDOUT)); 56 /* 57 Here a barrier is used to separate the two states. 58 */ 59 PetscCallMPI(MPI_Barrier(PETSC_COMM_WORLD)); 60 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 PetscCall(PetscPrintf(PETSC_COMM_SELF,"[%d] Jumbled Hello World\n",rank)); 67 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 PetscCall(PetscFinalize()); 76 return 0; 77 } 78 79 /*TEST 80 81 test: 82 83 TEST*/ 84