Open MPI logo

Open MPI User's Mailing List Archives

  |   Home   |   Support   |   FAQ   |  

This web mail archive is frozen.

This page is part of a frozen web archive of this mailing list.

You can still navigate around this archive, but know that no new mails have been added to it since July of 2016.

Click here to be taken to the new web archives of this list; it includes all the mails that are in this frozen archive plus all new mails that have been sent to the list since it was migrated to the new archives.

Subject: [OMPI users] File seeking with shared filepointer issues
From: Christian Anonymous (mpibot_at_[hidden])
Date: 2011-06-23 10:04:22


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?

<P><p><font face="Arial, Helvetica, sans-serif" size="2" style="font-size:13.5px">_______________________________________________________________<BR>Care2 makes it easy for everyone to live a healthy, green lifestyle
and impact the causes you care about most. Over 12 Million members!
http://www.care2.com

Feed a child by searching the web! Learn how http://www.care2.com/toolbar>