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Subject: Re: [OMPI users] Can't read values with MPI-IO
From: David O. Gunter (dog_at_[hidden])
Date: 2010-01-13 15:07:23


I noticed you never checked the return code from your MPI_File_read
statement. If you had used your own mpi() function, it would state
something like this:

MPI_FILE_READ(116): Cannot read from a file opened with amode MPI_MODE_WRONLY

-david

| Hi, i have this program, that write the rank of a process on a file.
| Every
| processes write the rank on the same file. Whe i try to read that value,
| is
| always zero.
|
|
| #include <stdio.h> /*IO stuff lives here*/
| #include <stdlib.h> /*exit lives here*/
| #include <mpi.h> /*MPI and MPI-IO live here*/
|
|
| //GLobal variables
| int rank;
|
| void mpi(int error_code){
|
| if (error_code != MPI_SUCCESS) {
|
| char error_string[BUFSIZ];
| int length_of_error_string, error_class;
|
| MPI_Error_class(error_code, &error_class);
| MPI_Error_string(error_class, error_string, &length_of_error_string);
| fprintf(stderr, "%3d: %s\n", rank, error_string);
| MPI_Error_string(error_code, error_string, &length_of_error_string);
| fprintf(stderr, "%3d: %s\n", rank, error_string);
| // send_error = TRUE;
| }
| }
|
| int main(int argc, char *argv[]){
|
| int size;
|
| MPI_File fh;
|
| MPI_Init(&argc, &argv);
|
| MPI_Comm_rank(MPI_COMM_WORLD, &rank);
| MPI_Comm_size(MPI_COMM_WORLD, &size);
|
| MPI_Errhandler_set(MPI_COMM_WORLD, MPI_ERRORS_RETURN);
|
| /*
| MPI_MODE_RDONLY --- read only,
| MPI_MODE_RDWR --- reading and writing,
| MPI_MODE_WRONLY --- write only,
| MPI_MODE_CREATE --- create the file if it does not exist,
| MPI_MODE_EXCL --- error if creating file that already exists,
| MPI_MODE_DELETE_ON_CLOSE --- delete file on close,
| MPI_MODE_UNIQUE_OPEN --- file will not be concurrently opened elsewhere,
| MPI_MODE_SEQUENTIAL --- file will only be accessed sequentially,
| MPI_MODE_APPEND --- set initial position of all file pointers to end of
| file.
| */
|
| MPI_Barrier(MPI_COMM_WORLD);
|
| //OPEN FILE
| // abertura do ficheiro
| //printf("[%d] - A abrir ficheiro\n", rank);
| mpi(MPI_File_open(MPI_COMM_WORLD, "buffer.io", MPI_MODE_CREATE |
| MPI_MODE_WRONLY, MPI_INFO_NULL, &fh));
| MPI_Barrier(MPI_COMM_WORLD);
|
|
| //calcular quantidade de bytes a escrever no ficheiro
| //MPI_Offset totalNumberOfIntegers
|
| //DEFINE OFFSET
| //definir o offset
| MPI_Offset myOffset = (MPI_Offset)(rank * sizeof(int));
| mpi(MPI_File_seek(fh, myOffset, MPI_SEEK_SET));
| MPI_Barrier(MPI_COMM_WORLD);
|
| //CHECK OFFSET
| // verificar a posição no ficheiro
| MPI_Offset myCurrentOffset;
|
| MPI_File_get_position(fh, &myCurrentOffset);
| printf ("[%d] - My current offset is %lld\n", rank, myCurrentOffset);
| MPI_Barrier(MPI_COMM_WORLD);
|
| //WRITE RANK IN THE FILE
| // escrita do ficheiro
| MPI_Status mpiStatus;
| int write=9;
|
| mpi(MPI_File_write(fh, &write, sizeof(int), MPI_BYTE, &mpiStatus));
| printf("[%d] - Escreveu no ficheiro o valor '%d'\n", rank, rank );
| MPI_Barrier(MPI_COMM_WORLD);
|
| //CALCULATE FILE SIZE
| //calcular quantidade de bytes a ler do ficheiro
| int numberOfBytes;
| MPI_Offset totalNumberOfBytes, numberOfBytesToRead;
|
| MPI_File_get_size(fh, &totalNumberOfBytes);
| numberOfBytesToRead = totalNumberOfBytes / size;
| numberOfBytes = (int) numberOfBytesToRead;
| printf("[%d] - A preparar para ler %d bytes\n", rank, numberOfBytes);
| MPI_Barrier(MPI_COMM_WORLD);
|
| //RESET OFFSET
| //restaurar valor inicial do offset
| myOffset = (MPI_Offset)(rank * sizeof(int));
| mpi(MPI_File_seek(fh, myOffset, MPI_SEEK_SET));
| MPI_Barrier(MPI_COMM_WORLD);
|
| //CHECK OFFSET
| // verificar a posição no ficheiro
| MPI_File_get_position(fh, &myCurrentOffset);
| printf ("[%d] - My current offset is %lld\n", rank, myCurrentOffset);
| MPI_Barrier(MPI_COMM_WORLD);
|
| //READ FILE
| //leitura do ficheiro
| int readBuffer=0;
| // MPI_Status mpiStatus;
| MPI_File_read(fh, &readBuffer, sizeof(int) , MPI_INT,
| MPI_STATUS_IGNORE);
| MPI_Barrier(MPI_COMM_WORLD);
| printf("[%d] - Leu do ficheiro o valor '%d'\n", rank, readBuffer );
| MPI_Barrier(MPI_COMM_WORLD);
|
| //CLOSE FILE
| // fecho do ficheiro
| MPI_File_close(&fh);
| MPI_File_delete("buffer.io", MPI_INFO_NULL );
|
| //end program
| MPI_Finalize();
|
| return(0);
|
| }
|
| --
| Cumprimentos
|
| Luís Miranda
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