Distributing Data to all Tasks

• Problem: read common data
  filetype = etype
  all tasks get all data (broadcast)
• new MPI routines:
  MPI_File_open(MPI_Comm comm, char *filename, int amode, MPI_Info info, MPI_File *fh)

  • opens file filename on all tasks in the group of comm
  • returns filehandle fh
  • access mode f.i.: MPI_MODE_RDONLY, MPI_MODE_RDWR, MPI_MODE_CREATE
  MPI_File_close(MPI_File *fh)

  • closes file
  MPI_File_set_view(MPI_File fh, MPI_Offset offset, MPI_Datatype etype, MPI_Datatype filetype, char *datarep, MPI_Info info)

  • creates view defined by offset, etype, filetype
  • defines data representation
  MPI_File_read(MPI_File fh, void *buf, int count, MPI_Datatype datatype, MPI_Status *status)

  • reads count elements of type datatype into buf
  • datatype must be a sequence of one or more etypes
  MPI_File_read_all(MPI_File fh, void *buf, int count, MPI_Datatype datatype, MPI_Status *status)

  • collective call: better optimisation may enhance performance
• Remarks to the programs (broadcast1.c, broadcast2.c)
  input file IN1 contains 100 integers a(i) with a(i) = 100-i
  can be created with the program create_files.c
  check for correct data in all tasks