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.TH "MPI_FILE_OPEN" "3" "Feb 06, 2024" "" "Open MPI"
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.sp
\fI\%MPI_File_open\fP — Opens a file (collective).
.SH SYNTAX
.SS C Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
#include <mpi.h>

int MPI_File_open(MPI_Comm comm, const char *filename,
     int amode, MPI_Info info,
     MPI_File *fh)
.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_OPEN(COMM, FILENAME, AMODE, INFO, FH, IERROR)
     CHARACTER*(*)   FILENAME
     INTEGER COMM, AMODE, INFO, FH, IERROR
.ft P
.fi
.UNINDENT
.UNINDENT
.SS Fortran 2008 Syntax
.INDENT 0.0
.INDENT 3.5
.sp
.nf
.ft C
USE mpi_f08
MPI_File_open(comm, filename, amode, info, fh, ierror)
     TYPE(MPI_Comm), INTENT(IN) :: comm
     CHARACTER(LEN=*), INTENT(IN) :: filename
     INTEGER, INTENT(IN) :: amode
     TYPE(MPI_Info), INTENT(IN) :: info
     TYPE(MPI_File), INTENT(OUT) :: fh
     INTEGER, OPTIONAL, INTENT(OUT) :: ierror
.ft P
.fi
.UNINDENT
.UNINDENT
.SH INPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBcomm\fP: Communicator (handle).
.IP \(bu 2
\fBfilename\fP: Name of file to open (string).
.IP \(bu 2
\fBamode\fP: File access mode (integer).
.IP \(bu 2
\fBinfo\fP: Info object (handle).
.UNINDENT
.SH OUTPUT PARAMETERS
.INDENT 0.0
.IP \(bu 2
\fBfh\fP: New file handle (handle).
.IP \(bu 2
\fBierror\fP: Fortran only: Error status (integer).
.UNINDENT
.SH DESCRIPTION
.sp
\fI\%MPI_File_open\fP opens the file identified by the filename
\fIfilename\fP on all processes in the \fIcomm\fP communicator
group. \fI\%MPI_File_open\fP is a collective routine; all processes
must provide the same value for \fIamode,\fP and all processes must
provide filenames that reference the same file which are textually
identical (note: Open MPI I/O plugins may have restrictions on
characters that can be used in filenames. For example, the ROMIO
plugin may disallow the colon (“:”) character from appearing in a
filename). A process can open a file independently of other processes
by using the MPI_COMM_SELF communicator. The file handle returned,
\fIfh,\fP can be subsequently used to access the file until the file is
closed using \fI\%MPI_File_close\fP\&. Before calling
\fI\%MPI_Finalize\fP, the user is required to close (via
MPI_File_close) all files that were opened with
\fI\%MPI_File_open\fP\&. Note that the communicator \fIcomm\fP is unaffected
by \fI\%MPI_File_open\fP and continues to be usable in all MPI
routines. Furthermore, use of \fIcomm\fP will not interfere with I/O
behavior.
.sp
Initially, all processes view the file as a linear byte stream; that is,
the \fIetype\fP and \fIfiletype\fP are both MPI_BYTE. The file view can be
changed via the \fI\%MPI_File_set_view\fP routine.
.sp
The following access modes are supported (specified in amode, in a
bit\-vector OR in one of the following integer constants):
.INDENT 0.0
.IP \(bu 2
\fBMPI_MODE_APPEND\fP
.IP \(bu 2
\fBMPI_MODE_CREATE\fP: Create the file if it does not exist.
.IP \(bu 2
\fBMPI_MODE_DELETE_ON_CLOSE\fP
.IP \(bu 2
\fBMPI_MODE_EXCL\fP: Error creating a file that already exists.
.IP \(bu 2
\fBMPI_MODE_RDONLY\fP: Read only.
.IP \(bu 2
\fBMPI_MODE_RDWR\fP: Reading and writing.
.IP \(bu 2
\fBMPI_MODE_SEQUENTIAL\fP
.IP \(bu 2
\fBMPI__MODE_WRONLY\fP: Write only.
.IP \(bu 2
\fBMPI_MODE_UNIQUE_OPEN\fP
.UNINDENT
.sp
The modes \fBMPI_MODE_RDONLY\fP, \fBMPI_MODE_RDWR\fP, \fBMPI_MODE_WRONLY\fP,
and \fBMPI_MODE_CREATE\fP have identical semantics to their POSIX
counterparts. It is erroneous to specify \fBMPI_MODE_CREATE\fP in
conjunction with \fBMPI_MODE_RDONLY\fP\&. Errors related to the access
mode are raised in the class \fBMPI_ERR_AMODE\fP\&.
.sp
On single\-node clusters, files are opened by default using nonatomic
mode file consistency semantics. The more stringent atomic\-mode
consistency semantics, required for atomicity of overlapping accesses,
are the default when processors in a communicator group reside on more
than one node. This setting can be changed using \fI\%MPI_File_set_atomicity\fP\&.
.sp
The \fI\%MPI_File_open\fP interface allows the user to pass information
via the \fIinfo\fP argument. It can be set to \fBMPI_INFO_NULL\fP\&. See the
\fI\%HINTS section\fP for a list of
hints that can be set.
.SH HINTS
.sp
The following hints can be used as values for the \fIinfo\fP argument.
.sp
\fBSETTABLE HINTS\fP
.INDENT 0.0
.IP \(bu 2
\fBMPI_INFO_NULL\fP
.IP \(bu 2
\fBshared_file_timeout\fP: Amount of time (in seconds) to wait for
access to the shared file pointer before exiting with
\fBMPI_ERR_TIMEDOUT\fP\&.
.IP \(bu 2
\fBrwlock_timeout\fP: 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 \fBMPI_ERR_TIMEDOUT\fP\&.
.IP \(bu 2
\fBnoncoll_read_bufsize\fP: Maximum size of the buffer used by MPI I/O
to satisfy multiple noncontiguous read requests in the noncollective
data\-access routines.
.sp
\fBNOTE:\fP
.INDENT 2.0
.INDENT 3.5
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 \fIread()\fP or \fIwrite()\fP 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 \fIread()\fP or \fIwrite()\fP (made at the MPI I/O level)
will access data not requested by this process in order to
reduce the total number of \fIwrite()\fP 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.
.UNINDENT
.UNINDENT
.IP \(bu 2
\fBnoncoll_write_bufsize\fP: Maximum size of the buffer used by MPI
I/O to satisfy multiple noncontiguous write requests in the
noncollective data\-access routines.
.sp
See the above note in \fBnoncoll_read_bufsize\fP\&.
.IP \(bu 2
\fBcoll_read_bufsize\fP: Maximum size of the buffer used by MPI I/O to
satisfy multiple noncontiguous read requests in the collective
data\-access routines.
.sp
See the above note in \fBnoncoll_read_bufsize\fP\&.
.IP \(bu 2
\fBcoll_write_bufsize\fP: Maximum size of the buffer used by MPI I/O
to satisfy multiple noncontiguous write requests in the collective
data\-access routines.
.sp
See the above note in \fBnoncoll_read_bufsize\fP\&.
.IP \(bu 2
\fBmpiio_concurrency\fP: (boolean) controls whether nonblocking I/O
routines can bind an extra thread to an LWP.  .sp
.IP \(bu 2
\fBmpiio_coll_contiguous\fP: (boolean) controls whether subsequent
collective data accesses will request collectively contiguous
regions of the file.
.UNINDENT
.sp
\fBNON\-SETTABLE HINTS\fP
.INDENT 0.0
.IP \(bu 2
\fBfilename\fP: Access this hint to get the name of the file.
.UNINDENT
.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
2003-2024, The Open MPI Community
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