NAME¶
MPI_File_preallocate - Preallocates a specified amount of storage space
at the beginning of a file (collective).
SYNTAX¶
C Syntax
#include <mpi.h>
int MPI_File_preallocate(MPI_File fh, MPI_Offset size)
Fortran Syntax (see FORTRAN 77 NOTES)¶
INCLUDE 'mpif.h'
MPI_FILE_PREALLOCATE( FH, SIZE, IERROR)
INTEGER FH, IERROR
INTEGER(KIND=MPI_OFFSET_KIND) SIZE
C++ Syntax¶
#include <mpi.h>
void MPI::File::Preallocate(MPI::Offset size)
- fh
- File handle (handle).
- size
- Size to preallocate file, in bytes (integer).
OUTPUT PARAMETER¶
- IERROR
- Fortran only: Error status (integer).
DESCRIPTION¶
MPI_File_preallocate ensures that storage space is allocated for the first
size bytes of the file associated with
fh. MPI_File_preallocate
can be a very time-consuming operation.
MPI_File_preallocate is collective; all processes in the group must pass
identical values for
size. Regions of the file that have previously
been written are unaffected. For newly allocated regions of the file,
MPI_File_preallocate has the same effect as writing undefined data. If size is
larger than the current file size, the file size increases to
size. If
size is less than or equal to the current file size, the file size is
unchanged.
The treatment of file pointers, pending nonblocking accesses, and file
consistency is the same as with MPI_File_set_size. If MPI_MODE_SEQUENTIAL mode
was specified when the file was opened, it is erroneous to call this routine.
FORTRAN 77 NOTES¶
The MPI standard prescribes portable Fortran syntax for the
SIZE argument
only for Fortran 90. FORTRAN 77 users may use the non-portable syntax
INTEGER*MPI_OFFSET_KIND SIZE
where MPI_OFFSET_KIND is a constant defined in mpif.h and gives the length of
the declared integer in bytes.
NOTES¶
When using the collective routine MPI_File_set_size on a UNIX file, if the size
that is set is smaller than the current file size, the file is truncated at
the position defined by size. If the size is set to be larger than the current
file size, the file size becomes the set size. When the file size is increased
this way with MPI_File_set_size, new regions are created in the file with
displacements between the old file size and the larger, newly set file size.
Sun MPI I/O does not necessarily allocate file space for such new regions. You
may reserve file space either by using MPI_File_preallocate or by performing a
read or write to certain 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.