I'm having some issues with MPI_File_seek_shared. Consider the following
small test C++ program
#include <iostream>
#include <mpi.h>
#define PATH "simdata.bin"
using namespace std;
int ThisTask;
int main(int argc, char *argv[])
{
MPI_Init(&argc,&argv); /* Initialize MPI */
MPI_Comm_rank(MPI_COMM_WORLD,&ThisTask);
MPI_File fh;
int success;
MPI_File_open(MPI_COMM_WORLD,(char *)
PATH,MPI_MODE_RDONLY,MPI_INFO_NULL,&fh);
if(success != MPI_SUCCESS){ //Successfull open?
char err[256];
int err_length, err_class;
MPI_Error_class(success,&err_class);
MPI_Error_string(err_class,err,&err_length);
cout << "Task " << ThisTask << ": " << err << endl;
MPI_Error_string(success,err,&err_length);
cout << "Task " << ThisTask << ": " << err << endl;
MPI_Abort(MPI_COMM_WORLD,success);
}
/* START SEEK TEST */
MPI_Offset cur_filepos, eof_filepos;
MPI_File_get_position_shared(fh,&cur_filepos);
//MPI_Barrier(MPI_COMM_WORLD);
MPI_File_seek_shared(fh,0,MPI_SEEK_END); /* Seek is collective */
MPI_File_get_position_shared(fh,&eof_filepos);
//MPI_Barrier(MPI_COMM_WORLD);
MPI_File_seek_shared(fh,0,MPI_SEEK_SET);
cout << "Task " << ThisTask << " reports a filesize of " << eof_filepos
<< "-" << cur_filepos << "=" << eof_filepos-cur_filepos << endl;
/* END SEEK TEST */
/* Finalizing */
MPI_File_close(&fh);
MPI_Finalize();
return 0;
}
Note the comments before each MPI_Barrier. When the program is run by
mpirun -np N (N strictly greater than 1), task 0 reports the correct
filesize, while every other process reports either 0, minus the filesize
or the correct filesize. Uncommenting the MPI_Barrier makes each process
report the correct filesize. Is this working as intended? Since
MPI_File_seek_shared is a collective, blocking function each process
have to synchronise at the return point of the function, but not when
the function is called. It seems that the use of MPI_File_seek_shared
without an MPI_Barrier call first is very dangerous, or am I missing
something?
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