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.\" Man page generated from reStructuredText.
.
.TH "MPI_FILE_PREALLOCATE" "3" "May 30, 2025" "" "Open MPI"
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.sp
\fI\%MPI_File_preallocate\fP — Preallocates a specified amount of storage
space at the beginning of a file (collective).
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>
int MPI_File_preallocate(MPI_File fh, MPI_Offset size)
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE MPI
! or the older form: INCLUDE \(aqmpif.h\(aq
MPI_FILE_PREALLOCATE(FH, SIZE, IERROR)
INTEGER FH, IERROR
INTEGER(KIND=MPI_OFFSET_KIND) SIZE
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE mpi_f08
MPI_File_preallocate(fh, size, ierror)
TYPE(MPI_File), INTENT(IN) :: fh
INTEGER(KIND=MPI_OFFSET_KIND), INTENT(IN) :: size
INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT/OUTPUT PARAMETER
.INDENT 0.0
.IP \(bu 2
\fBfh\fP: File handle (handle).
.UNINDENT
.SH INPUT PARAMETER
.INDENT 0.0
.IP \(bu 2
\fBsize\fP: Size to preallocate file, in bytes (integer).
.UNINDENT
.SH OUTPUT PARAMETER
.INDENT 0.0
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_File_preallocate\fP ensures that storage space is allocated for the
first \fIsize\fP bytes of the file associated with \fIfh\fP\&.
\fI\%MPI_File_preallocate\fP can be a very time\-consuming operation.
.sp
\fI\%MPI_File_preallocate\fP is collective; all processes in the group must pass
identical values for \fIsize\fP\&. Regions of the file that have previously
been written are unaffected. For newly allocated regions of the file,
\fI\%MPI_File_preallocate\fP has the same effect as writing undefined data. If
size is larger than the current file size, the file size increases to
\fIsize\fP\&. If \fIsize\fP is less than or equal to the current file size, the
file size is unchanged.
.sp
The treatment of file pointers, pending nonblocking accesses, and file
consistency is the same as with \fI\%MPI_File_set_size\fP\&. If
\fBMPI_MODE_SEQUENTIAL\fP mode was specified when the file was opened, it is
erroneous to call this routine.
.SH NOTES
.sp
When using the collective routine \fI\%MPI_File_set_size\fP 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 \fI\%MPI_File_set_size\fP, new
regions are created in the file with displacements between the old file
size and the larger, newly set file size.
.sp
Sun MPI I/O does not necessarily allocate file space for such new
regions. You may reserve file space either by using \fI\%MPI_File_preallocate\fP
or by performing a read or write to certain bytes.
.SH ERRORS
.sp
Almost all MPI routines return an error value; C routines as the return result
of the function and Fortran routines in the last argument.
.sp
Before the error value is returned, the current MPI error handler associated
with the communication object (e.g., communicator, window, file) is called.
If no communication object is associated with the MPI call, then the call is
considered attached to MPI_COMM_SELF and will call the associated MPI error
handler. When MPI_COMM_SELF is not initialized (i.e., before
\fI\%MPI_Init\fP/\fI\%MPI_Init_thread\fP, after \fI\%MPI_Finalize\fP, or when using the Sessions
Model exclusively) the error raises the initial error handler. The initial
error handler can be changed by calling \fI\%MPI_Comm_set_errhandler\fP on
MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI
argument to mpiexec or info key to \fI\%MPI_Comm_spawn\fP/\fI\%MPI_Comm_spawn_multiple\fP\&.
If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN
error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error
handler is called for all other MPI functions.
.sp
Open MPI includes three predefined error handlers that can be used:
.INDENT 0.0
.IP \(bu 2
\fBMPI_ERRORS_ARE_FATAL\fP
Causes the program to abort all connected MPI processes.
.IP \(bu 2
\fBMPI_ERRORS_ABORT\fP
An error handler that can be invoked on a communicator,
window, file, or session. When called on a communicator, it
acts as if \fI\%MPI_Abort\fP was called on that communicator. If
called on a window or file, acts as if \fI\%MPI_Abort\fP was called
on a communicator containing the group of processes in the
corresponding window or file. If called on a session,
aborts only the local process.
.IP \(bu 2
\fBMPI_ERRORS_RETURN\fP
Returns an error code to the application.
.UNINDENT
.sp
MPI applications can also implement their own error handlers by calling:
.INDENT 0.0
.IP \(bu 2
\fI\%MPI_Comm_create_errhandler\fP then \fI\%MPI_Comm_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_File_create_errhandler\fP then \fI\%MPI_File_set_errhandler\fP
.IP \(bu 2
\fI\%MPI_Session_create_errhandler\fP then \fI\%MPI_Session_set_errhandler\fP or at \fI\%MPI_Session_init\fP
.IP \(bu 2
\fI\%MPI_Win_create_errhandler\fP then \fI\%MPI_Win_set_errhandler\fP
.UNINDENT
.sp
Note that MPI does not guarantee that an MPI program can continue past
an error.
.sp
See the \fI\%MPI man page\fP for a full list of \fI\%MPI error codes\fP\&.
.sp
See the Error Handling section of the MPI\-3.1 standard for
more information.
.SH COPYRIGHT
2003-2025, The Open MPI Community
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