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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)
INPUT/OUTPUT PARAMETER
fh File handle (handle).
INPUT PARAMETER
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 previ-
ously 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_SEQUEN-
TIAL 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 argu-
ment only for Fortran 90. FORTRAN 77 users may use the non-portable
syntax
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_preallo-
cate 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++ func-
tions 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.
Open MPI 1.2 September 2006 MPI_File_preallocate(3OpenMPI)
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