bionic (3) MPI_File_set_view.openmpi.3.gz

NAME

       MPI_File_set_view - Changes process's view of data in file (collective).

SYNTAX

C Syntax

       #include   <mpi.h>   int   MPI_File_set_view(MPI_File   fh,  MPI_Offset  disp,       MPI_Datatype  etype,
       MPI_Datatype filetype,      const char *datarep, MPI_Info info)

Fortran Syntax (see FORTRAN 77 NOTES)

       USE MPI
       ! or the older form: INCLUDE 'mpif.h'
       MPI_FILE_SET_VIEW(FH, DISP, ETYPE,
            FILETYPE, DATAREP, INFO, IERROR)
            INTEGER   FH, ETYPE, FILETYPE, INFO, IERROR
            CHARACTER*(*)  DATAREP
            INTEGER(KIND=MPI_OFFSET_KIND) DISP

C++ Syntax

       #include <mpi.h>
       void MPI::File::Set_view(MPI::Offset disp,
            const MPI::Datatype& etype,
            const MPI::Datatype& filetype, const char* datarep,
            const MPI::Info& info)

INPUT/OUTPUT PARAMETER

       fh        File handle (handle).

INPUT PARAMETERS

       disp      Displacement (integer).

       etype     Elementary data type (handle).

       filetype  File type (handle). See Restrictions, below.

       datarep   Data representation (string).

       info      Info object (handle).

OUTPUT PARAMETER

       IERROR    Fortran only: Error status (integer).

DESCRIPTION

       The MPI_File_set_view routine changes the process's view of the data in the file -- the beginning of  the
       data  accessible  in the file through that view is set to disp; the type of data is set to etype; and the
       distribution of data to processes  is  set  to  filetype.   In  addition,  MPI_File_set_view  resets  the
       independent file pointers and the shared file pointer to zero. MPI_File_set_view is collective across the
       fh; all processes in the group must pass identical values for  datarep  and  provide  an  etype  with  an
       identical  extent.   The  values for disp, filetype, and info may vary. It is erroneous to use the shared
       file pointer data-access routines unless identical values for disp and filetype are also given. The  data
       types passed in etype and filetype must be committed.

       The disp displacement argument specifies the position (absolute offset in bytes from the beginning of the
       file) where the view begins.

       The MPI_File_set_view interface allows the user to pass a data-representation string to MPI I/O  via  the
       datarep  argument.  To  obtain  the  default  value  (or  "native"),  pass  NULL.  The user can also pass
       information via the info argument. See the HINTS section for a list of hints that can be  set.  For  more
       information, see the MPI-2 standard.

HINTS

       The following hints can be used as values for the info argument.

       SETTABLE HINTS:

       - MPI_INFO_NULL

       -  shared_file_timeout:  Amount of time (in seconds) to wait for access to the shared file pointer before
       exiting with MPI_ERR_TIMEDOUT.

       - rwlock_timeout: Amount of time (in seconds) to wait for obtaining a read or write lock on a  contiguous
       chunk of a UNIX file before exiting with MPI_ERR_TIMEDOUT.

       -  noncoll_read_bufsize:   Maximum  size  of  the  buffer used by MPI I/O to satisfy read requests in the
       noncollective data-access routines. (See NOTE, below.)

       - noncoll_write_bufsize: Maximum size of the buffer used by MPI I/O to  satisfy  write  requests  in  the
       noncollective data-access routines. (See NOTE, below.)

       -  coll_read_bufsize:   Maximum  size  of  the  buffer  used  by  MPI I/O to satisfy read requests in the
       collective data-access routines. (See NOTE, below.)

       - coll_write_bufsize:  Maximum size of the buffer used by MPI  I/O  to  satisfy  write  requests  in  the
       collective data-access routines. (See NOTE, below.)

       NOTE:  A  buffer  size smaller than the distance (in bytes) in a UNIX file between the first byte and the
       last byte of the access request causes MPI I/O to iterate and perform multiple  UNIX  read()  or  write()
       calls. If the request includes multiple noncontiguous chunks of data, and the buffer size is greater than
       the size of those chunks, then the UNIX read() or write() (made at the MPI I/O level)  will  access  data
       not  requested  by this process in order to reduce the total number of write() calls made. If this is not
       desirable behavior, you should reduce this buffer size to equal the size of the contiguous chunks  within
       the aggregate request.

       -  mpiio_concurrency:  (boolean) controls whether nonblocking I/O routines can bind an extra thread to an
       LWP.

       - mpiio_coll_contiguous: (boolean) controls whether subsequent  collective  data  accesses  will  request
       collectively contiguous regions of the file.

       NON-SETTABLE HINTS:

       - filename: Access this hint to get the name of the file.

FORTRAN 77 NOTES

       The  MPI  standard prescribes portable Fortran syntax for the DISP argument only for Fortran 90.  FORTRAN
       77 users may use the non-portable syntax

            INTEGER*MPI_OFFSET_KIND DISP

       where MPI_OFFSET_KIND is a constant defined in mpif.h and gives the length of  the  declared  integer  in
       bytes.

ERRORS

       Almost  all  MPI  routines  return  an  error  value; C routines as the value of the function and Fortran
       routines in the last argument. C++ functions do not return errors. If the default error handler is set to
       MPI::ERRORS_THROW_EXCEPTIONS,  then  on  error  the  C++  exception  mechanism  will  be used to throw an
       MPI::Exception object.

       Before the error value is returned, the current MPI error handler is called. For MPI I/O function errors,
       the  default  error  handler  is  set  to  MPI_ERRORS_RETURN.  The  error  handler  may  be  changed with
       MPI_File_set_errhandler; the predefined error handler MPI_ERRORS_ARE_FATAL may be used to make I/O errors
       fatal. Note that MPI does not guarantee that an MPI program can continue past an error.