#include<stdio.h>#include<stdlib.h>#include<string.h>#include"mpi.h"/** * blocking read/write in the context of a specific process's fileview * * int MPI_File_read(MPI_file fh, void * buf, int count, MPI_Datatype datatype, MPI_Status * status); * * int MPI_File_write(MPI_file fh, void * buf, int count, MPI_Datatype datatype, MPI_Status * status) */int main(int argc, char *argv[]){int totalTaskNum, rankID;MPI_Init(&argc, &argv);MPI_Comm_rank(MPI_COMM_WORLD, &rankID);MPI_Comm_size(MPI_COMM_WORLD, &totalTaskNum);char *filename = "file.txt";MPI_File fh;MPI_Status status;MPI_File_open(MPI_COMM_WORLD, filename, MPI_MODE_CREATE | MPI_MODE_RDWR, MPI_INFO_NULL, &fh);MPI_Offset offset = rankID * 128;//each process will has its file view which starts with offsetMPI_File_set_view(fh, offset, MPI_CHAR, MPI_CHAR, "native", MPI_INFO_NULL);MPI_Offset seek_offset = 0;int whence = MPI_SEEK_SET;//after set fileview, the seek is the context of new fileviewMPI_File_seek(fh, seek_offset, whence);//write start with seek's positionchar write_buf[128];sprintf(write_buf, "rankID = %d, totalTaskNum = %d\n", rankID, totalTaskNum);MPI_File_write(fh, write_buf, strlen(write_buf), MPI_CHAR, &status);//after write, the position has been moved, so let's go back via seekMPI_Offset seek_offset2 = 0;int whence2 = MPI_SEEK_SET;//after set fileview, the seek is the context of new fileviewMPI_File_seek(fh, seek_offset2, whence2);//read start with seek's positionchar read_buf[128];MPI_File_read(fh, read_buf, sizeof(read_buf), MPI_CHAR, &status);printf("rankID = %d, content = \'%s\'\n", rankID, read_buf);/*//after reading, the current offset has moved to a new positionMPI_Offset curr_offset;MPI_File_get_position(fh, &curr_offset);printf("==rankID = %d, curr_offset = %lld\n", rankID, curr_offset);//get physical_offset from fileview's curr_offsetMPI_Offset physical_offset;MPI_File_get_byte_offset(fh, curr_offset, &physical_offset);printf("==rankID = %d, physical_offset = %lld\n", rankID, physical_offset);*/MPI_File_close(&fh);//after open, fh has the communicator infoMPI_Finalize();return 0;}
