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Asked: 2026-05-23T04:17:35+00:00

I am writing an MPI program that needs to read a part of a

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I am writing an MPI program that needs to read a part of a file into memory, one piece at a time, with each piece going to an available process. I am therefore using a shared filepointer. The first part of the file is a header which I want to read to read and distribute to all processes, I have managed to do this by reading it on the master process and broadcasting it to all other processes.

The next part of the file is a long (in theory up to several gigabytes) array of float triples. I want to set the fileview for all the processes so that it starts at the beginning of this array, and each process should be able to see the whole array. Furthermore, and this is my real problem, I do not want the processes to see beyond this array, so that after they encounter the last set of 3 floats they report EOF. So in practice each process just sees one long 3-float array and nothing else.

After the header has been read this is my code:

MPI_Datatype particle_type;
MPI_Type_contiguous(3,MPI_FLOAT,&particle_type);
MPI_Type_commit(&particle_type);
MPI_Offset cur_file_pos;
MPI_File_get_position_shared(fh,&cur_file_pos);
MPI_File_set_view(fh, cur_file_pos, particle_type, particle_type, (char *) "native", MPI_INFO_NULL); /* fh is the file-handle from MPI_File_open */

As I understand, this simply skips the header, but the file view does not stop after the array, it continues into the next part of the file which I am not interested in. Can anyone help me with this simple problem? I have not been able to find any thorough explanations (with examples) of file views anywhere.

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1 Answer

  1. Editorial Team

    Unfortunately, MPI_File_set_view won’t do this for you; once you go beyond the filetype the filetype repeats. While MPI_File_set_view will allow you to partition the view of the file between processes, it won’t let you “truncate” the view of the file like this.

    If you’re using the shared file pointer, presumably the simplest thing to do is to loop until the new position == number of particles (once the view is set, the file pointer is in units of etypes).

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